the 
 various pore architectures of zeolites give these catalyst materials 
 unique properties for shape selectivity toward reactants , products , 
 and transition states .
combination with catalytic activity 
 makes zeolites relevant catalysts for chemical processes , such as 
 isomerization , alkylation , and cracking reactions .
fluid catalytic 
 cracking ( fcc ) is a central process in petrochemistry in which zeolites , 
 such as zeolite y and zsm-5 , are utilized .
investigations have , therefore , been carried out 
 on model systems , such as coffin - shaped zsm-5 crystals .
these crystals are composed of six subunits and have proven to be 
 ideal for detailed microscopic investigations due to their micrometer 
 size , as shown in the schematic drawing of figure 1 .
their long axis is surrounded by four rectangular pyramidal 
 subunits , whose tips join in the very center of the crystal 
the top and bottom subunits 
 fill the remaining inner volume , and roof - like top forms the surface 
 on either end of the long axis .
a detailed structural investigation 
 was recently presented by ristanovic et al . , who performed xrd experiments to determine the crystallographic 
 structure of each single subunit .
their common crystallographic c axis was parallel to the crystals long axis , and 
 the four pyramidal subunits had an identical crystallographic orientation 
 when being opposite , and it was 90 rotated for neighboring units . 

this structural relationship was also confirmed by polarized light 
 microscopy and ebsd / sem investigations .
also , a 3-component model has been proposed for coffin - shaped 
 zsm-5 crystals , in which an additional subunit is located in the very 
 center of the crystal .
suggest this 3-component model 
 to be the preferred one for coffin - shaped zsm-5 crystals .
the crystal structure of zsm-5 was monoclinic 
 and orthorhombic before and after addition of probe molecules , respectively , 
 such as , e.g. , styrene derivates .
large coffin - shaped 
 zsm-5 crystal : the model shows the six subunits 
 and the internal pore architecture for sinusoidal and straight pores . 
 a 4-fluorostyrene monomer is shown in the lower center , which was 
 used to create linear and cyclic fluorescent dimeric carbocations , 
 illustrated on the right side inside the zsm-5 channel framework .
the adsorption of probe molecules 
 inside the channel framework 
 of zsm-5 has proven to be a useful methodology to investigate the 
 reactivity of these samples .
vis absorption 
 microspectroscopy reveals spectral features of the products formed 
 inside the zeolite pores .
styrene derivates , as 
 will be used in our investigation , form both cyclic and linear dimeric 
 carbocation species , with absorption bands at around 490 and 580 nm , 
 respectively .
zeolite zsm-5 has a three - dimensional ( 3-d ) internal pore network , 
 consisting of narrow straight and sinusoidal channels with sizes of 
 5.3  5.6  and 5.1  5.5  , respectively .
straight channels are running along the crystallographic b vector , i.e. , , and sinusoidal channels are perpendicular 
 along the a vector , i.e. , .
molecules , which are adsorbed in those channels are , therefore , 
 strictly oriented . also , the diffusion properties are influenced by 
 the internal channel network ; caro et al .
followed the uptake of n - hexane in large coffin - shaped zsm-5 crystals with a microbalance 
 and found a three times higher diffusion coefficient perpendicular 
 to the crystal s long axis compared to diffusion parallel to 
 it , which was confirmed by interference 
 microscopy imaging .
absorption 
 and emission of light are polarization - dependent processes . 
 in particular , the degree of alignment of the transition dipole moment 
 vector ( of a specific molecule ) with the polarization plane of the 
 incoming light determines the intensity of absorption . the reverse 
 process ( i.e. , emission ) , therefore , releases plane - polarized light . 

this anisotropic spectroscopic information was related to structural 
 characteristics of such zsm-5 crystals for absorption spectroscopy and emission spectroscopy .
were able to record activity maps for furfuryl alcohol condensation 
 inside zsm-5 crystals ( supported by ebsd investigations ) , where they 
 found the rim to be the most active toward this reaction .
additionally , 
 they observed the molecules in the center of the top and bottom subunits 
 to be aligned perpendicular to the surface , whereas the molecules 
 in the reactive rim were aligned parallel to the surface and the short 
 axis of the crystal .
the origin of polarized fluorescence microscopy 
 can be found in 
 the field of life sciences , e.g. , the location , molecular orientations , 
 and behavior inside lipid and cell membranes ( with excellent reviews and chapters describing this field in more 
 detail ) .
it is , however , also a highly attractive methodology to investigate 
 molecules inside zeolite pores .
therein , zeolite l is of great interest for , 
 e.g. , the absorption 
 of dyes for laser applications .
the one - dimensional 
 channels in the crystalline structure of zeolite l provide an ideal 
 architecture to investigate molecular orientation and interaction 
 ( through fluorescence live time measurements ) .
employed this type of zeolite to determine the polarization of various 
 fluorescence bands of dye molecules .
megelski 
 et al . observed the orientation of three different dye molecules inside 
 zeolite l. the largest of those ( i.e. , popop ) could only be oriented 
 along the direction of the zeolite channels , whereas oxonine and pyronine 
 were able to be positioned with half cone angles up to 40 and 
 30 with respect to the channel direction .
furthermore , the location and orientation of molecules 
 inside zeolite channels was observed by multiplex coherent anti - stokes 
 raman scattering ( mcars ) .
2-d slices of 2-chlorothiophene inside large coffin - shaped 
 zsm-5 crystals were recorded , in which the intensity pattern of these 
 head - to - tail oriented probe molecules revealed the subunit structure 
 of such crystals in detail .
such mfi - type 
 zeolite materials were employed by seebacher et al . to visualize mesostructures 
 and , hence , crystalline defects and spatial 
 distribution of probe molecules inside these pores .
this methodology was further developed to determine and 
 quantify molecular dynamics inside microporous alpo4 - 5 
 crystals and mesoporous m41s thin films .
the molecular characteristics 
 ( i.e. , orientation , wavelength , and intensity of emission ) were correlated 
 to the direct environment of the probe molecule .
steaming of zeolites is a common postsynthesis treatment 
 procedure to alter its characteristics , e.g. , acidity and diffusion . 

the diffusion inside the microporous zsm-5 framework was increased 
 due to the formation of mesopores and , hence , loss of crystallinity , which 
 could also be visualized by the location of large fluorescing dye 
 molecules inside large coffin - shaped zsm-5 crystals after steam treatment 
 due to the creation of mesopores . besides 
 this degradation of the crystalline zeolite framework
part of the framework aluminum 
 t sites are removed upon steaming and transfer into extra - framework 
 aluminum sites .
the values in parentheses 
 are calculated 
 on the basis of the molecular structures shown .
other molecular structures , 
 including the position of the positive charge and related resonance 
 structures , are possible , and the theoretical spectral transition 
 values provided should only be seen as a trend line , i.e. ,  
 ( cyclic dimeric carbocation ) <  ( linear dimeric carbocation ) 
 <  ( trimeric carbocation ) , and spectral transitions present 
 in the visible region of the spectrum . here we present a systematic confocal polarized fluorescence 
 microscopy 
 investigation of large coffin - shaped zsm-5 .
we opted for the fluorostyrene 
 oligomerization reaction as our previous work has indicated that this 
 is a powerful and sensitive reaction for assessing brnsted acid 
 sites in zeolite - based materials , including zeolite zsm-5 .
table 1 highlights the different carbocations formed , including 
 their spectroscopic fingerprints , as measured by uv  vis and synchrotron - based ir microspectroscopy , and their 
 possible molecular structures and related dimensions .
the confocal 
 fluorescence maps created in this manuscript are to be seen in relation 
 to the recent work of ristanovic et al . , who provided a detailed -xrd investigation on the very same 
 zeolite crystal batches .
the current contribution shows in detail 
 where ( i.e. , in which 
 zeolite channel and part of the crystal ) fluorescent molecules are 
 situated due to their strict orientation inside the channels .
the 
 location of these fluorescent molecules could also be distinguished 
 from their fluorescence spectral features .
furthermore , the influence 
 of steaming on the pore architecture of zeolite zsm-5 and , therefore , 
 the diffusion into the crystal as well as the orientation of the fluorescent 
 molecules is revealed .
three batches 
 of large coffin - shaped zsm-5 crystals , i.e. , parent , 
 steamed at 500 c , and steamed at 700 c , were stained with 
 4-fluorostyrene as a probe molecule .
the fluorescence of the oligomerized 
 4-fluorostyrene formed within the zeolite channels was recorded for 
 405 , 457 , 488 , 514 , 561 , and 642 nm laser excitation .
the crystals , 
 positioned in both a roof and a gable position , were oriented parallel , 
 45 ( parent and steamed 700 c ) , and perpendicular with 
 respect to the polarization plane of the incoming laser light .
hence , 
 the data set consists of 96 z - series , and each of those consist of 
 18 focal planes , of which each focal plane is a summarized image of 
 32 real fluorescence color images ( 10 nm  32 channels ) .
a graphical 
 overview of this approach is given in figure 2 , and details about the instrumentation can be found in figure s1 , supporting information .
summary of experiments 
 and evaluation principle of the multilaser 
 excitation confocal fluorescence microscopy approach used : three sets 
 of large coffin - shaped zsm-5 samples ( parent and steamed at 500 and 
 700 c ) were stained with 4-fluorostyrene as probe molecule . 

both roof and gable positions at 0 , 45 ( for parent and 
 steamed 700 c ) , and 90 orientation were investigated for 
 their fluorescence during 405 , 457 , 488 , 514 , 561 , and 642 nm laser 
 excitation .
eighteen focal planes were recorded , each consisting of 
 32 real color images ( i.e. , integral intensity of a 10 nm range , 400720 
 nm and 430750 nm , respectively ) .
hence , the presented data 
 set contains a total of 96 sets of focal planes .
afterward , during 
 data evaluation , 3-d ( i.e. , depth dependent ) spectra were extracted 
 for each set of focal planes from a region of interest .
figure 3 shows the absorption spectra and optical images 
 of the parent , steamed 500 c , and 700 c zsm-5 crystals . 

all stained zsm-5 crystals showed absorptions at around 550 , 515 , 
 and one at 580 nm , shifted to longer wavelength ( 605 and 635 nm ) . 

it was previously described in the literature , as summarized in table 1 , that the absorption band at the shortest wavelength 
 belongs to the cyclic dimeric carbocation , whereas the most intense 
 band at 550 nm represents the linear dimeric carbocation .
absorption bands at longer wavelength are due to higher oligomers , 
 most probably a trimeric carbocation , as demonstrated in table 1 . in view of the uncertainty 
 of the latter spectral assignment we opted to limit our discussions 
 to the cyclic and dimeric carbocations .
after impregnation with 4-fluorostyrene 
 and subsequent temperature treatment , all crystals appeared in a characteristic 
 pink color due to the formed styrene oligomers inside the zeolite 
 pores .
the steamed 500 c crystals appear , in comparison to the 
 other two batches , in a more intense , slightly darker color , as illustrated 
 in figure 3 .
( a ) absorption spectra of the zsm-5 crystals ; 
 ( b ) parent , ( c ) steamed 
 500 c , and ( d ) steamed 700 c presented as photoimages . 

those were the very same crystals investigated in the fluorescence 
 microscopy investigations in this manuscript and obtained after impregnation 
 and reaction of 4-fluorostyrene at 180 c .
polarization - dependent 
 absorption spectroscopy investigations were presented for parent and 
 steamed 700 c in sprung et al . and 
 figure s4 , supporting information , respectively . 

figure s3 , supporting information illustrates 
 interference images of the state of the crystals impregnated with 
 4-fluorostyrene and washed , before the oligomerization was initiated . 
 the four lids , which terminate the zsm-5 crystal on all four long 
 facets ( cf .
figure 1 ) , do not show any noticeable 
 interference , in contrast to the center pyramid reaching out to the 
 crystal tips . in roof position
a clear hourglass pattern was observed , 
 which was not the case in gable position .
the former statement was 
 confirmed by an image of a ( so - called ) mixed crystal , in which one - half 
 of the zeolite zsm-5 crystal was rotated by 90 ; hence , there 
 was always a roof and gable tip present at the same time . here
, only 
 this half , which was in a roof position , did show the formerly described 
 hourglass pattern . in order to assist the reader , 

we have chosen three sections to 
 present the results , i.e. , orientation and location 
 of molecules trapped in the zeolite channels , spectral features of molecules trapped in the zeolite 
 channels , and influence of steaming on 
 the location of molecules , which are meant to be a guideline . 

the results may of course not be strictly divided as such , and cross - links 
 to other features occur .
the observed polarization plane of emitted 
 fluorescence light was always vertical ( i.e. , north  south ) . 

the cross 
 was oriented as such that for one of the two crystals each roof area 
 of the tip was positioned perpendicular to the recorded polarization 
 plane .
any features , which were observed for crystal orientations other than 
 0 and 90 , were , therefore , considered to appear in an 
 equal manner at the respective other side of the zsm-5 crystal ( due 
 to symmetry ) in case the crystal would be rotated 90 from that 
 ( e.g. , 45 and 45 ) .
figure 4 illustrates crystals in roof and gable orientation of all 
 three zsm-5 batches .
let us first focus on orientation - related features : 
 parent zsm-5 crystals , which were oriented with its long axis parallel 
 to the analyzer position , showed a rim of fluorescence on the outer 
 edge of the crystal .
rotating the crystal by 90 , to be aligned perpendicular to the 
 analyzer position , made the center appear fluorescent .
highlight a 
 in figure 4 shows a focal plane around the 
 center of the crystal .
it is pointed out here that with increasing 
 depth the intensity of emitted light was strongly decreasing .
intense absorption of excitation light in the upper layers of the 
 crystal significantly reduced the fluorescence intensity inside the 
 crystal .
the tip of the crystal viewed in roof position ( highlighted 
 as b in figure 4 ) was fluorescent in both 0 
 and 90 orientation , which was most pronounced for excitation 
 frequencies ex= 561 nm . in the gable 
 position this inner part of the tip triangle was dark ( highlight c ) . 

the tip part in the gable position revealed another feature , marked 
 by d. when oriented to 45 with respect to the analyzer position , 
 only one part of the tip was observed .
it was confirmed by preliminary 
 experiments that this observation was symmetric and may therefore 
 be translated to the other part of the tip , cf .
the spectral intensities 
 of the same spot in 0 and 45 orientation were similar . 
 in highlight
e the edge remains dark when the crystal was in 90 
 orientation , hence , complementary to the observed fluorescent rim 
 in 0 orientation .
figure 5 illustrates 
 the complementary information 
 gathered from the presented experiments : when viewed from both directions , 
 an hourglass pattern appeared . in gable position
, this was revealed 
 by a large fluorescing area , which shrunk toward the center of the 
 crystal and increased again in deeper layers .
figure 5a nicely illustrates this observation by a high fluorescence 
 intensity at the top and bottom layers compared to the center . in 
 contrast to that
viewing the crystal in roof position shows 
 an hourglass pattern as well , however , from the side .
the fluorescence 
 intensity in a region between the crystal center and the tip ( figure 5c ) remains high all the way through the crystal . 

in contrast , a region of interest somewhere between the crystal s 
 center and long edge confirms the hourglass pattern with its narrow 
 center ; and a high emission intensity was only observed in the top 
 layers ( cf .
figure 6a , b shows 
 the complementary information gathered by observing the crystals 
 fluorescence in 0 and 90 orientations . in gable orientation 

the fluorescence of the roof parts of the tips were most intense , 
 in comparison to the long edges , and observed from top to bottom . 

it can clearly be seen in figure 6a how narrow 
 this fluorescing volume was .
exactly this aforementioned volume did 
 not appear ( fluorescent ) when the crystal was turned to the 90 
 orientation .
similar observations for the crystal s 
 long edge in roof position are illustrated in figure 6b .
combined view on orientation and steaming related features of zsm-5 
 crystals stained with 4-fluorostyrene : ex = 561 
 nm , highlights a  e are described in the text .
zeolite zsm-5 crystal , steamed at 700 c , viewed in roof and 
 gable orientation , excited with a 642 nm laser .
schematic drawing 
 of the crystal is completed by focal planes of the top , middle , and 
 bottom plane ( with respect to the viewing direction ) .
arrows indicate 
 the area from which depth - dependent spectra were extracted : ( a , c ) 
 left of center , ( b , d ) center , and ( e ) top of center .
double - headed 
 arrows indicate the recorded polarization plane , i.e. , perpendicular 
 to the long crystal axis .
( a , b ) location : the rim , which is fluorescent 
 in the vertical crystal , 
 is not fluorescent in the horizontal one . (
a ) zeolite zsm-5 crystal 
 was steamed at 500 c and excited at 488 and 561 nm in horizontal 
 and vertical orientations , respectively .
( c , d ) spectral features : 
 crystals were steamed at 700 c and excited at 488 nm ; the schematic 
 drawings highlight the polarization plane of recorded fluorescence 
 light .
the tips were observed to be fluorescent for both 
 0 and 90 
 orientation . for a comprehensive overview
the scheme of figure 6c illustrates the 
 polarization plane of the recorded fluorescence light .
the fluorescence 
 spectrum ( figure 6 g ) expresses the fact that 
 this fluorescence was observed along the whole depth of the crystal . 

now , the crystal is rotated in figure 6c around 
 its long axis ; the crystal would now be in roof position , i.e. , as 
 in figure 6b .
hence , the channels in the tip 
 part , which was highlighted in figure 6c , are 
 oriented presumably along the crystal s long axis .
this suits 
 the pore structure model of such zsm-5 crystals , and the latter mentioned 
 observed fluorescence polarization behavior originates from molecules 
 entrapped inside those sinusoidal channels of the tip region .
another conclusion may be drawn by comparing 
 figure 6c and 6d . in 
 both orientations ,
thus , the fluorescence light was polarized perpendicular to the outer 
 tip surface in the gable orientation and additionally parallel to 
 the crystal s short axis . due to the strict orientation behavior 
 of the recorded fluorescence light , it could be speculated whether 
 these two spectral features originated from the same molecule .
the 
 crystallographic model of the zsm-5 crystal , illustrated in figure 1 , contains straight and sinusoidal channels . following 
 this model
, the fluorescence in gable position was originating mainly 
 from molecules aligned inside the sinusoidal channels .
fluorescence 
 ( of the crystal tip ) in roof position was then emitted by molecules 
 inside straight pores .
spectra extracted from those regions reveal 
 features which substantiate the formerly proposed statement : all three 
 spectra in figure 6g  i show a band at 
 530/540 nm . in figure 6 g
, however , appeared 
 an additional band at 580 nm , which was missing in both spectra taken 
 in roof position ( figure 6h , i ) .
such a spectral 
 difference was also observed between the very same region investigated 
 in 0 and 90 orientation , as illustrated in figure 6e , f . in figure
6f the fluorescence 
 at longer wavelength ( i.e. , 610620 nm ) was more intense than 
 in figure 6e .
in summary , a longer wavelength 
 fluorescence occurred in 0 orientation in comparison to 90 
 orientation .
furthermore , comparing the spectra in figure 6 g and 6h highlights the depth 
 sensitivity of the spectral features .
the band at 530 nm was observed 
 for the whole crystal depth of just part of it , respectively , according 
 to the crystals shape .
depth - dependent fluorescence 
 spectra were extracted from ( a ) the tip , ( b ) body between tip and 
 center , and ( c ) center region .
figure 7 provides a comprehensive overview 
 of depth - dependent spectra extracted from three regions ( i.e. , tip , 
 between tip and center , and center of the crystal ) of a parent crystal 
 in 0 orientation and gable position .
all extracted spectra were 
 scaled with respect to the most intense fluorescence band in the region 
 of interest among all excitation lines .
the highest emission intensity was observed 
 for 488 nm excitation in figure 7a , whereas 
 it was more intense for 561 nm excitation in figure 7c .
this corresponds to the observed absorption bands reported 
 in the section on visible microspectroscopy .
a bathochromic shift 
 in the overall fluorescence intensity was observed toward the crystal s 
 center ( i.e. , from figure 7a to 7c ) .
this is most clearly seen for the shift of the fluorescence 
 band for 514 nm excitation .
the most intense emission for 457 nm excitation 
 was observed in region b ( between center and tip ) .
an intense emission was observed for 488 nm excitation at 
 530 nm ; those for 514 , 561 , and 642 nm were low in intensity . toward 
 the center of the crystal , a second band appeared at 590 nm . the fluorescence 
 band for 514 nm excitation shifts from 550 nm at the tip to 590 and 
 600 nm toward the center of the crystal , respectively .
the latter 
 band might have reached out further into the red part of the spectrum . 
 however , the 457/514 dichroic mirror did cut the light for wavelengths 
 greater than 630 nm .
an emission band with high intensity at 600 nm 
 was extracted from the crystal s body ( i.e. , figure 7b , c ) for 561 nm excitation .
it was , however , observed 
 with low intensity at the crystal s tip .
the emission characteristic 
 for 642 nm excitation followed those observed for 561 nm excitation , 
 i.e. , low / negligible intensity at the tip with increasing emission 
 intensity toward the center of the crystal . due to the weaker absorption 
 of the 642 nm laser in the upper layers ,
the investigated set of parent zsm-5 crystals , 
 fully described in the previous section , were additionally steamed 
 at 500 and 700 c , also called mildly and severely treated in 
 the literature , respectively .
parent crystals ( in the 
 upper part of this figure ) showed a narrow rim of emission in 0 
 orientation for both gable and roof position .
the center part of the 
 crystal remained largely dark ; thus , no emission of this polarization 
 was recorded from that region .
crystals , which were steamed at 500 
 c , did show already a significant broadening of the fluorescent 
 rim reaching out into the center .
crystals in roof position 
 did literally show a complementary fluorescence pattern when compared 
 in 0 and 90 orientations .
for steamed crystals at 
 700 c , it seems that a kind of a small replicate of the large 
 crystal s shape was observed inside the crystal .
our results suggest for the samples investigated here the 
 validity of the 2-component model , and figures s3 and s4 ( second crystal 
 on the lower right corner ) , supporting information , provide the basis for this conclusion .
furthermore , steam 
 treatment apparently decreased the amount of fluorescent molecules 
 in the outer crystal layers .
the absorption of excitation light decreases 
 in these regions ; hence , the emission of molecules in deeper layers 
 toward the center could therefore be observed .
the center part remained dark for a parent crystal ; however , 
 for a crystal steamed at 700 c the inner subunit structure could 
 clearly be observed . such degradation of the zeolite framework and 
 the creation of mesopores were also observed and confirmed by aramburo 
 et al .
figure 8 illustrates gable - positioned crystals 
 in 90 orientation as parent and steamed at elevated temperatures 
 excited at 488 nm .
parent crystals showed a uniform fluorescence representing 
 the whole crystal shape , which was clearly different from the very 
 same crystal excited at 561 nm ( cf .
those crystals , which 
 were treated in steam at 500 and 700 c , respectively , did not 
 show emission from the tip parts in this orientation .
a fluorescence 
 band at 530 nm was observed in figure 8a and 
 8c . in the latter ,
treated at 700 c 
 in steam , a second band at 650 nm appeared also in deeper layers . 

a clearly two - divided fluorescence map was recorded for 500 c 
 steam - treated zsm-5 crystals .
their tip parts , note without the formerly 
 described rim ( cfr . figure 6a ) , emitted bright 
 yellow light at 520 nm , whereas the center part emitted orange - red 
 light at around 650 nm .
influence of steaming : zsm-5 crystals ( parent , 
 steamed ( st ) 500 
 c , and steamed ( st ) 700 c ) in gable position oriented 
 90 with respect to the analyzer position ; excitation wavelength 
 was 488 nm . depth - dependent fluorescence spectra from ( a  c ) 
 the center part of the crystal and ( d ) the yellow tip part .
the obtained 
 absorption spectra , shown in figure 3 , are 
 in line with previously reported spectra of oligomerized 4-fluorostyrene 
 inside large zeolite zsm-5 crystals by stavitski et al . the crystal batch after mild steaming conditions 
 ( i.e. , 500 c ) showed a higher absorption at longer wavenumbers , 
 compared to parent crystals , which was also found on zeolite zsm-5 
 powder samples .
the more intense coloration 
 for mildly compared to parent and severely steamed crystals was confirmed 
 in investigations by aramburo et al . , who 
 concluded an increasing and decreasing activity ( i.e. , reactivity 
 and therefore formation of colored reaction products ) with increasing 
 steaming temperature .
the experiments demonstrate the strict polarization 
 of fluorescence 
 light , originating from molecules entrapped inside the zeolite pore 
 system ( cf .
figures 4 , 6 , and s5 , supporting information ) . in 
 the experimental section data recording and treatment it was considered 
 that the transition dipole moment vector is parallel ( or at least 
 within 20 ) with respect to the long axis of the oligomeric reaction 
 products .
thus , for further interpretation 
 of the results the recorded polarization plane of fluorescence light 
 is parallel to the long axis of an elongated oligomeric species , which 
 is oriented parallel to a channel direction of the zeolite . for clarity , 
 the pore architecture of zeolite zsm-5 , as shown in figure 1 ,
shall be briefly repeated ; straight pores are 
 oriented parallel to the short axis of the crystal for the four pyramidal 
 subunits ( which is along ) , and sinusoidal pores are oriented 
 perpendicular to the straight pores and parallel to . for the 
 closing units ,
the straight pores are parallel to the rectangular 
 facets and hence open to the triangular facets .
a strong fluorescence signal was recorded parallel to   for the 
 pyramidal subunits ; hence , molecules were oriented along the straight 
 pores in these sections .
the value added by the results 
 in figure 4 was the observation of a fluorescent 
 rim , showing emission polarized parallel to the crystal s long 
 axis .
similarly , a rim of absorption light polarized along the long 
 crystal axis , including the tips , was reported by sprung et al . , employing differently polarized light for uv 
vis 
 absorption microscopy ( in this reference figure 1 , note the different 
 orientation of the polarizer and analyzer , respectively , cf . the images 
 labeled with 0 ) . also , roeffaers et al . observed a fluorescent rim during furfuryl condensation .
their conclusion 
 ( by ebsd ) and ours for this observation 
 was / is that this fluorescence was originating from molecules inside 
 the sinusoidal channels .
in connection to the last argument 
 in the former paragraph , why 
 did this observed fluorescent rim not originate from randomly oriented 
 species on the zeolite surface ?
first , a rinsing step was performed 
 before inducing the reaction by a temperature increase to minimize / exclude 
 such reaction at the outer crystal surface .
second , crystals in gable 
 position and 90 orientation did not show any fluorescence of 
 the tip region ( cf . figure 4 ) . in a more focused 
 manner , this is presented in figure s5 , supporting 
 information .
hence , this fluorescence light was strictly polarized 
 and , thus , originated from molecules inside the zeolite pores .
sinusoidal 
 pores open into the { 100 } faces , however , not perpendicular ( in that 
 case no fluorescence would have been observed ) . for the tip region , 
 it is suggested , based on the observations made in figures s5 , supporting information , and 6c , that the sinusoidal pores are open perpendicular to the 
 roof areas of the tip . following
the observations made in figure 4 for parent and steamed samples , it can be speculated 
 whether this observed fluorescent rim is an intrinsic characteristic 
 of the diffusion and reactivity of such a zsm-5 crystal . it might 
 also be considered that this was already the sign of a degrading pore 
 architecture / mesopore creation due to postsynthesis treatment ( e.g. , 
 calcination ) . after steam treatment a clear increase of this fluorescent 
 rim was observed toward the center of the crystal .
the outer layers 
 of the crystals seem to decrease in crystallinity ; the absorption 
 of excitation light was much lower for mildly and severely steamed 
 crystals , i.e. , fluorescence of center parts of the crystal could 
 be recorded ( cf .
this aspect was 
 also observed for visible absorption microscopy , shown in figure s4 , supporting information .
another question , 
 which might arise in connection with figure 4 and the illustration of parent crystals in the 
 upper part is why has no fluorescence been observed from probe molecules 
 inside sinusoidal channels from the bulk of the crystal , hence , from 
 the intact framework ?
sinusoidal channels are open to the majority 
 of the outer surface of such zsm-5 crystals and were therefore at 
 first in contact with the liquid 4-fluorostyrene .
it is assumed that 
 both sinusoidal and straight channels were filled with monomeric 4-fluorostyrene 
 molecules before their oligomerization was initiated , as illustrated 
 schematically by kox et al .
two major products were assumed to be present 
 after oligomerization , i.e. , a cyclic and a linear dimeric carbocation .
cyclic dimers are therefore only expected 
 to be formed at zeolite zsm-5 channel intersections or defect sites / defected 
 pores in the crystal , where enough room is provided for this molecule . 
 in view of their molecular dimensions and
shape we assume that this 
 idea also applies for the trimeric carbocations , as illustrated in 
 figure 1 .
in contrast , linear dimeric carbocations 
 are assumed along straight channels only , due to the fact that such 
 a dimer is determined longer ( with a length of 14.3  ) than the dimensions of sinusoidal channels , which 
 are only 12  in length ( center to center straight channel ) . 

hence , an intact and defect - free framework ( no postsynthesis steam 
 treatment ) may exclusively incorporate linear dimeric carbocations 
 inside straight channels , whereas cyclic dimeric carbocations are 
 formed at channel intersections due to their steric demands .
the visible spectra 
 in figure 3 report the highest absorption for 
 550 nm , followed by 580 and 515 nm .
thus , there 
 was only a clear assignment for a corresponding absorption band for 
 the latter .
all other observed emission intensities for the remaining 
 excitation lines remain roughly below half - maximum intensity ( cf . 

figure 7 ) . their emission intensity may be 
 explained by the overlap of an excitation line with the remainder 
 of a broad absorption band . unlike all other excitation lines ,
these 
 ramps and terraces on the ( 010 ) face of the pyramidal subunits for 
 parent crystals were not observed for 488 nm excitation ( cf .
an absorption band for the 488 nm laser 
 line is , however , missing .
it might be speculated whether its origin 
 is to be found in a double - excitation process of a uv band ( which 
 exists in the suspected wavelength range ) . due to the methodology of applying depth - dependent fluorescence 
 spectra ,
local spectral features were revealed . in the section orientation and location of molecules trapped in the 
 zeolite channels the location of molecules was discussed and 
 concluded .
molecules in the outer tip region were aligned inside sinusoidal 
 pores , whereas in the bulk part of the tip they were inside straight 
 pores ( cf .
fluorescence spectra 
 extracted from these regions , in which molecules inside sinusoidal 
 pores were observed , revealed a shoulder which was 20 and 40 nm shifted 
 compared to the spectra of molecules in straight pores , for 561 and 
 488 nm excitation , respectively . within this content , it is important 
 to compare the spectral features in figure 6e , 6f , and 6g  i . 

the straight pores are slightly wider in dimension in comparison to 
 the sinusoidal pores .
if the same molecular species is situated inside 
 straight and sinusoidal pores , however , with a different steric environment , 
 that constrains the molecule and therefore shifts the emission band .
steaming had a highly significant influence on the fluorescence 
 spectra for 488 nm excitation ( cf .
upon steaming at 500 c a red emission around 650 nm appeared 
 in the center of the crystal bulk , whereas the closing subunits on 
 either long end remained bright yellow ( around 530 nm ) .
this red fluorescence 
 was observed with much less intensity for severely steamed crystals . 

a volcano - like behavior could therefore be proposed for the recorded 
 wavelength of fluorescence light , which can be related to the molecule 
 itself , or the interaction of the same molecule with different channel 
 environments .
explained an enhanced activity after mild steaming 
 by a synergism between nonframework sites and framework brnsted 
 sites rather than an increase of the acidity of hydroxyl groups .
reported 
 this volcano trend for the very same samples by vis microspectroscopy 
 investigations .
the observed spectral feature in figure 8 is , therefore , considered to be related to the brnsted 
 acid strength inside the zeolite pores .
the interaction of the acid 
 site with the oligomeric species may , thus , cause the spectral shift 
 into the red region . 
two molecular species ( i.e. , the cyclic and linear dimeric 
 cations ) are in focus .
their different uv  vis absorption bands allowed us to visualize selectively one or the other species by 
 choosing the appropriate laser excitation frequency .
hence , fluorescence 
 observed for 488 nm excitation is associated with the location of 
 the cyclic dimeric carbocation species ( cf .
thus , the linear dimeric 
 carbocation species appears fluorescent after 561 nm excitation ( cf . 

this is a great potential of the employed multilaser excitation 
 confocal fluorescence microscopy approach .
table 2 summarizes the observed locations of both product oligomeric 
 species . due to the steric demands of the cyclic dimeric carbocation 

linear 
 dimeric carbocation species were mainly located in straight channels , 
 however close to the surface ( i.e. , the rim ) , and at postsynthesis 
 treated crystals those species also occupy sinusoidal channels .
the 
 fluorescence spectra of molecules inside sinusoidal channels revealed 
 a band / shoulder at longer wavelength compared to the spectra of the 
 same species inside straight channels ( in the same region ) .
this distinction 
 was possible only due to the strict alignment of the crystals under 
 the microscope .
the different locations were 
 either occupied ,  , or not occupied , . symbol in parentheses 
 refers to observations at higher temperatures .
the introduction of chemical imaging methods has resulted in a 
 wealth of fundamental information on the interplay between guest molecules 
 and porous host materials , including zeolites . in this work ,
a systematic polarized fluorescence confocal microscopy 
 investigation was presented of three sets of zeolite zsm-5 crystals 
 ( i.e. , parent , steamed 500 c , and 700 c ) .
fluorescence 
 spectra were recorded with a spectral range of 320 nm and a spectral 
 resolution of 10 nm for 405 , 457 , 488 , 514 , 561 , and 642 nm laser 
 excitation and translated into the third dimension .
structural features 
 were determined visually ( by inspecting the focal planes and its polarization 
 dependent fluorescence ) and spectroscopically ( by 3-d fluorescence 
 spectra , distinguishing chemical species ) .
the orientation of elongated 
 fluorescent molecules was recorded on a micrometer scale and linked 
 to the pore architecture of the zeolite .
on the basis of this 
 innovative characterization approach we can 
 make the following conclusions on the 3-d host  guest chemistry 
 of the linear and cyclic dimeric fluorostyrene carbocations , shown 
 in figure 1 and table 1 , within the zeolite zsm-5 framework.(1)in parent zsm-5 crystals a large portion 
 of the molecules were situated inside the straight pores along the 
  crystal direction , which accommodate exclusively the linear 
 dimeric carbocations.(2)in parent zsm-5 crystals it was possible 
 to visualize ( and proof ) fluorescence originating from the sinusoidal 
 channels as well , which was located in a rim around the crystal .
these 
 sinusoidal pores were oriented perpendicular to the rectangular tip 
 surface.(3)this rim was 
 the onset of pore structure 
 degradation , which was ( already ) observed for parent crystals ( template 
 removal procedure ) and increased upon increasing postsynthesis steaming 
 temperature .
hence , more linear dimeric carbocation molecules were 
 observed in sinusoidal channels inside the zeolite crystals toward 
 the center of the crystal , and their increased presence can be regarded 
 as a handy spectroscopic marker for zeolite zsm-5 degradation . in 
 other words ,
the developed approach could be used for quality control 
 purposes of freshly prepared zeolite zsm-5 crystals.(4)the location of molecules could in 
 addition to its orientation be distinguished by their spectral features . 

cyclic and linear dimeric carbocations inside the sinusoidal pores 
 showed an additional fluorescence band shifted to longer wavelength 
 by 40 and 20 nm ( for 561 and 488 nm excitation ) , respectively , compared 
 to the same dimeric carbocations inside the straight pores.(5)postsynthesis steaming 
 of zeolite 
 zsm-5 revealed a volcano - type behavior of the recorded fluorescence , 
 suggesting an optimal steaming temperature for a significantly altered 
 interaction between the zeolite material and the staining molecule 
 used for assessing the location of the brnsted acid sites . in parent
zsm-5 crystals a large portion 
 of the molecules were situated inside the straight pores along the 
  crystal direction , which accommodate exclusively the linear 
 dimeric carbocations . in parent
zsm-5 crystals it was possible 
 to visualize ( and proof ) fluorescence originating from the sinusoidal 
 channels as well , which was located in a rim around the crystal .
this rim was 
 the onset of pore structure 
 degradation , which was ( already ) observed for parent crystals ( template 
 removal procedure ) and increased upon increasing postsynthesis steaming 
 temperature .
hence , more linear dimeric carbocation molecules were 
 observed in sinusoidal channels inside the zeolite crystals toward 
 the center of the crystal , and their increased presence can be regarded 
 as a handy spectroscopic marker for zeolite zsm-5 degradation . in 
 other words ,
the developed approach could be used for quality control 
 purposes of freshly prepared zeolite zsm-5 crystals .
the location of molecules could in 
 addition to its orientation be distinguished by their spectral features . 

cyclic and linear dimeric carbocations inside the sinusoidal pores 
 showed an additional fluorescence band shifted to longer wavelength 
 by 40 and 20 nm ( for 561 and 488 nm excitation ) , respectively , compared 
 to the same dimeric carbocations inside the straight pores .
postsynthesis steaming 
 of zeolite 
 zsm-5 revealed a volcano - type behavior of the recorded fluorescence , 
 suggesting an optimal steaming temperature for a significantly altered 
 interaction between the zeolite material and the staining molecule 
 used for assessing the location of the brnsted acid sites .
although a specific type of zeolite framework 
 structure ( i.e. , 
 mfi ) was employed in this work , the presented methodology is transferable 
 to other types of zeolite framework structures ( e.g. , fau and mor ) 
 in which linear dimeric and cyclic dimeric fluorostyrene species can 
 reside .
furthermore , one may envisage other scientific endeavors in 
 which optical and spectral resolutions , molecular location , and orientation 
 of guest molecules in the third dimension may be of great interest . 

the multilaser excitation confocal fluorescence microscopy toolbox 
 has now been developed to make such detailed studies possible .
large zsm-5 
 crystals ( 20  20  100 m ) were provided by exxonmobil 
 and used in its acid form .
the samples were placed on a borosilicate 
 glass in an open linkam cell ( ftir 600 , linkam scientific instruments ) . 
 at a temperature of 30 c , the samples were impregnated with 
 an excess of 4-fluorostyrene ( 99% , sigma - aldrich , used as received ) . 

after the reactant had evaporated the sample was rinsed twice with 
 mesitylene ( 97% , sigma - aldrich , used as received ) for cleaning purposes . 

since it can be expected that mesitylene does not diffuse into the 
 pores of zsm-5 , only excess reactant ( fluorostyrene ) from the outside 
 of the crystals was assumed to be rinsed off during this procedure . 

the reaction was initiated by increasing the temperature rapidly to 
 180 c , at which it was kept during all investigations .
an upright optical microscope 
 from olympus ( bx 41 ) was employed in reflectance mode , equipped with 
 a 50 0.5 na dry objective and a 30 w halogen lamp .
incoming 
 light was plane polarized in the e  w plane ( i.e. , east  west , 
 horizontally oriented ) through an u - po3 polarizer from olympus . reflected 

light was recorded with a ccd video camera ( colorview iiiu , soft imaging 
 system gmbh ) and observed through a 50/50 double view - port tube .
the 
 reflected light was analyzed with a rotatable analyzer u - an360 from 
 olympus .
this device was completed by an angular scale to increase 
 the precision of adjusting its orientation .
the sample was oriented 
 manually under the objective to positions of 15 steps , and the 
 analyzer position was adjusted to steps of 30 with respect to 
 the polarization plane of incoming light .
hence , at each crystal orientation 
 ( 0 , 15 , 30 , ... , 165 ) six analyzer positions 
 ( 0 , 30 , 60 , ... , 150 ) were recorded .
fluorescence 
 microscopic investigations were performed with a nikon eclips 90i 
 confocal microscope in reflectance mode ; its essential optical parts 
 are illustrated in figure s1 , supporting information .
excitation light was provided by an ensemble of four laser heads , 
 of which one was tunable in its output frequency ; thus , laser light 
 of 405 , 457 , 488 , 514 , 561 , and 642 nm was employed .
laser light passed 
 the polarizer inside the instrument after the dichroic mirror ( dm ) 
 and before it was focused through a 100 0.73 na dry lens on 
 the sample .
thus , the emission light did pass the same polarizer before 
 the dichroic mirror on the way to the analyzing unit .
the polarization 
 plane of excitation / emission light was , therefore , the same , i.e. , 
 n  s ( i.e. , north  south , vertically oriented ) .
optical 
 multimode fibers carried excitation light and fluorescence light from 
 the sources to the microscope and to the spectral analyzer , respectively . 

the microscope was equipped with a nikon a1 scan head , which accommodated 
 the optics to couple fiber optics for excitation and emission light 
 with the microscope , and the dichroic mirrors .
a linkam cell ( ftir 
 600 , linkam scientific instruments ) was mounted 
 on the sample stage of the microscopes to supply heat .
an in - house 
 made rotatable sample holder ( stainless steel ) was employed to orient 
 the sample with respect to the incoming light polarization plane .
the spectral analyzer in the 
 nikon a1 system was equipped with 32 photomultiplier tubes ( pmts ) 
 to collect the emission light in the 400720 nm ( for ex = 405 nm ) and 430750 nm ( all other laser lines ) 
 range with a resolution of 10 nm . the sample ( large zsm-5 crystals ) 

was oriented with its long axis parallel , at 45 , and perpendicular 
 with respect to the polarization plane of incoming laser light . a 
 z - series of 18 focal planes was taken for each orientation and laser 
 line with a step size of 1.2 m . thus , every z - series contained 
 18  32 images of 512  128 pix , with a pixel 
 size of 0.22 m and a pixel dwell of 57.2 s . before exporting 
 the images they were adjusted for brightness according to the optimal 
 conditions of the brightest image of that z - series by the instrument 
 software ( nikon elements ar ) .
for clarification of terms a z - series 
 consisted of 18 focal planes , and each focal plane is a sum of 32 
 images , which represent the intensity of light in a 10 nm range .
the narrow pore channels of zsm-5 contain ( in comparison to that ) 
 rather large styrene derivate molecules and its oligomeric condensation 
 products .
therefore , a strict anisotropic behavior is expected and 
 considered for the polarization - dependent experiments described here .
the angle between absorption 
 and emission axis was assumed to be < 20 , as found by investigations 
 for similar molecules .
this was confirmed 
 in preliminary experiments for the oligomeric reaction products investigated 
 here .
we consider , therefore , that the elongated reaction products 
 of styrene derivate condensation have their transition dipole moment 
 vectors aligned along the long axis of the molecule for both adsorption 
 and emission .
correction for laser reflection : spectra of reflected 
 laser light ( observed for laser lines > 457 nm ) are illustrated 
 in 
 figure 9 , which show the reflections at shorter 
 and longer wavelength with respect to the dichroic mirror position . 

the reflection 
 at lower wavelength was found to be a useful benchmark ; it is unaffected 
 during the investigations , since fluorescence light does appear at 
 longer wavelength with respect to the excitation frequency ( for single - excitation 
 processes ) .
it was , therefore , possible to correct all images ( for 
 excitation with 488 , 514 , 561 , and 642 nm laser light ) for their laser 
 reflection .
both reflection spectra in a bare crystal and the sample 
 holder were fairly similar ; however , the reflection spectra in the 
 crystal were eventually used for correction .
figure 9c  e illustrate the result of the following procedure , 
 exemplified for three images for 514 , 561 , and 642 nm excitation . 
 for every focal plane ,
the image of the channel , which represents 
 the maximum intensity of the laser reflection at lower wavelength , 
 with respect to the dichroic mirror , was taken as benchmark . the intensity 
 of the pixels in these benchmark images
were then multiplied by the 
 value of the relative intensity of the laser reflection spectrum of 
 a specific wavelength range ( cf .
the resulting intensity values were then subtracted from 
 the pixel intensities of the respective channel .
( for example , ex = 488 nm , i.e. , benchmark for subtraction is channel 5 , 
 image to correct is channel 4 .
pixels of the image from channel 5 
 are multiplied with the value of channel 4 in the reflection spectrum 
 ( cf .
the resulting pixel intensities 
 are subtracted from the raw data image of channel 4 . )
( a , b ) laser reflection 
 spectra for 488 , 514 , 561 , and 642 nm laser 
 lines , recorded on a glass sample holder and on bare zsm-5 crystal . 

subtraction of laser reflection for ( c ) 642 , ( d ) 561 , and ( e ) 514 
 nm laser light at steamed 700 c zsm-5 crystals .
the spot beneath 
 the crystals of the images in the left column was originating from 
 the laser reflected in the sample holder .
the signal of this reflection 
 was effectively subtracted from the images by the procedure described 
 in the text ( compare images in the left and right columns ) .
the dichroic mirrors 
 405/488 and 457/514 did transmit light with a wavelength < 630 nm . 

this cuts a large portion of the fluorescence light in the red region , 
 illustrated in figure 10a , d .
this drawback 
 could , at least for 488 nm excitation , be circumvented by recording 
 the same z - series twice with the 405/488 and 405/488/561 dichroic 
 mirror inserted , respectively .
the latter dichroic mirror , obviously , 
 does not transmit light in a narrow region around 561 nm , which is 
 clearly illustrated in figure 10b , e .
thus , 
 images of channels < 600 nm and 600 nm were combined ( cf .
figure 10c and 10f ) and represent 
 from now on the data set taken at 488 nm excitation .
transmission of fluorescence 
 light of dichroic mirrors and 488 
 nm excitation : ( ac ) parent and ( d  f ) steamed 500 c 
 zsm-5 crystal , spectra extracted for ( a , d ) dichroic mirror 405/488 
 and ( b , e ) dichroic mirror 405/488/561 .
all spectra were recorded with optimal 
 optical conditions , i.e. , laser intensity , detector gain , and image 
 brightness .
an at least semiquantitative description of the achieved 
 fluorescence signals was , however , desirable .
therefore , a normalization 
 procedure was applied as follows : a square of 10  10 pix was defined in every focal plane outside the crystal , picking 
 up the image / background noise caused by the detector gain .
the average 
 intensity value of these 100 pixel was additionally averaged over 
 all 18 focal planes in this z - series .
figure s2a , supporting information , illustrates these values after 10 
 repetitions and their standard deviation .
for further data processing , 
 the average noise was then normalized by the number of pixels ( i.e. , 
 100 ) .
hence , each z - series was assigned a noise - intensity per pix value , which was utilized to semiquantify all fluorescence 
 spectra .
figure s2b  d , supporting information , shows focal planes of a steamed 700 c zsm-5 crystal for 488 , 
 514 , and 561 nm excitation .
their fluorescence spectra , extracted 
 from the whole crystal without the tips , in figure s2e , supporting information , were not normalized and 
 represent an average of the intensities in that region of interest . 

normalized fluorescence spectra ( figure s2f , supporting 
 information ) show a different order of intensities among the 
 three excitation lines compared to uncorrected spectra .
a large part of the results and discussion sections consists of 3-d 
 spectra , which 
 represent depth - dependent fluorescence spectra of a region of interest 
 ( roi ) ; figure 2 illustrates this principle . 

such a roi , a rectangle , was freely adjusted to the size of the area 
 of interest in the images .
the values for each channel in that roi 
 were then summed up and divided by its size in pix .
finally , 
 the spectra were normalized with respect to the assigned noise - intensity 
 per pix value .
all data treatment described in this section 
 has been carried out with homemade matlab scripts ( matlab r2009a ) . 

image processing was ( in most cases ) carried out in the hsv - color 
 space in which the third matrix represents the pixel intensity .
the 
 whole data set including the commented matlab script to extract 3-d 
 fluorescence spectra is available in the supporting 
 information .
the theoretical 
 approach was applied previously to gain insight into the thiophene 
 oligomerization products formed on zeolite zsm-5-containing extrudates .
the optimized geometry for each compound was 
 obtained using the hybrid meta gga density functional m06 - 2x with the 6 - 31+g(d , p ) standard basis set .
all 
 harmonic vibrational frequencies were real ; therefore , the structures 
 were minima on the potential energy surface .
time - dependent ( td ) dft 
 excited states calculations were carried out at m06 - 2x/6 - 31+g(d , p ) 
 level .
all images , which 
 appear from the results section on , are oriented 
 as they were recorded , i.e. , the incoming 
 light polarization for visible microscopy is e  w ( i.e. , parallel 
 to the short axis of the sheet of paper ) , and for fluorescence microscopy 
 it is n  s ( i.e. , parallel to the long axis of the sheet of 
 paper ) .
the short axis of all fluorescence images represents 28.2 
 m , and scale bars represent 10 m in width .
 a detailed 
 and systematic polarized confocal fluorescence microscopy 
 investigation is presented on three batches of large coffin - shaped 
 zsm-5 crystals ( i.e. , parent , steamed at 500 c , and steamed 
 at 700 c ) . in total , six laser lines of different wavelength 
 in the visible region are employed on two crystal positions and three 
 orientations with respect to the polarization plane of the excitation 
 laser light . 
 a fluorescent probe molecule is generated inside the 
 zeolite pores , originating from the acid - catalyzed oligomerization 
 of 4-fluorostyrene . 
 a thorough analysis of the polarization plane 
 of emitting fluorescent light reveals insight into the orientation 
 of the fluorescent probe molecule restricted by the highly ordered 
 zeolite channel framework , thereby visualizing pore accessibility 
 and clearly distinguishing the occupation of straight and sinusoidal 
 channels by the probe molecule . 
 spectral features are , furthermore , 
 observed to tell apart molecules situated in one or the other pore . 
 
 special focus was given on the rim and tip regions of the zeolite 
 zsm-5 crystals . 
 on the basis of the confocal approach of the investigation , 
 the aforementioned features are evaluated in three dimensions , while 
 the degradation of the zeolite framework upon postsynthesis steam 
 treatment could be visualized by occupation of the sinusoidal pores . 
Introduction
Results
Discussion
Conclusions
Experimental Section
Clarification