the immense and diverse potential of phthalocyanines ( pc ) in a variety of technical 
 ( chemical sensors , liquid crystals , electrocatalysis , and nonlinear 
 optics ) and medicinal ( primarily photodynamic therapy [ 58 ] ) applications 
 has generated a great deal of interest in these macrocyclic compounds .
this , 
 together with the extraordinary stability of these complexes , has resulted in 
 considerable research being carried out on the phthalocyanine complex upon 
 incorporation of nearly all metals in the periodic table into the pc core .  
complexes 
 with metalloids and nonmetals of groups iva and va are of particular interest 
 due to the two different valence / oxidation states available to the central 
 atom
. triazatetrabenzcorroles 
 ( tbc ) are phthalocyanine - like compounds which have lost one of the bridging 
 nitrogen atoms .
the 
 synthesis of ge , si , ga , and al tbc complexes have been reported [ 10 , 11 ] .
were the first to report on the synthesis and unusual electronic spectra 
 of the pcp compared to pcp [ 9 , 13 ] .
it became apparent 
 that upon complexation with the trivalent phosphorous , a bridging nitrogen was 
 lost to form the phosphorous oxide tetrabenzcorroles ( ptbc ) .
since then , a number of octa- and 
 tetrasubstituted ptbc derivatives have been synthesized [ 1419 ] .
high fluorescence quantum 
 yields   and singlet oxygen quantum yields   have been reported for the 
 complexes .
the water - soluble tetrasulphonated ptbc showed good photodynamic 
 therapy towards hela cells . for applications in pdt ,
high triplet 
 lifetimes and yields are desired ; however there are no reports on the triplet - state 
 behavior of the ptbc complexes . in this 
 work
, we report on ptbc complexes tetra- or octasubstituted with chloride and 
 bromide ring substituents ( see schemes 1 and 2 ) , since the halogens are expected to 
 enhance intersystem crossing , resulting in high triplet yields due to the heavy 
 atom effect .
a ptbc derivative 
 containing a mixture of butoxy and chloro ring substituents has been reported 
 , but no photophysical data has been reported for halogenated ptbcs .
  dimethylsulfoxide 
 ( dmso ) , methanol ( meoh ) , phosphorous tribromide ( pbr3 ) , deuterated 
 chloroform ( cdcl3 ) , deuterated dimethylsulfoxide ( dmso - d6 ) , deuterated pyridine 
 ( pyr - d5 ) , 4,5 
 dichlorophthalonitrile , 1,8-diazabicyclo undec-7-ene ( dbu ) , 
 4-nitrophthalonitrile , copper ( i ) bromide , copper ( i ) chloride , hydrobromic 
 acid , hydrochloric acid , palladium on carbon ( pd / c ) , and dicyanobenzene were 
 purchased from sigma - aldrich ( miss , usa ) and used as received . pyridine and 
 1-pentanol were obtained from sigma - aldrich and dried prior to use .
ground - state 
 electronic absorption spectra were recorded on a varian cary 500 uv - vis - nir 
 spectrophotometer .
h and c nmr spectra were obtained using 
 a bruker amx 400  mhz and a bruker avance ii+ 600  mhz nmr spectrometer . 

fluorescence emission and excitation spectra were recorded on a varian cary 
 eclipse spectrofluorimeter , while ft - ir spectra ( kbr pellets ) were recorded on 
 a perkin - elmer spectrum 2000 ft - ir spectrometer .
triplet 
 absorption and decay kinetics were recorded on a laser flash photolysis system , 
 the excitation pulses were produced by an nd : yag laser ( quanta - ray , 1.5  j/90  ns ) pumping a dye laser ( lambda physic fl 3002 , pyridin 1 in methanol ) .
the 
 analyzing beam source was from a thermo oriel xenon arc lamp , and a 
 photomultiplier tube was used as detector .
signals were recorded with a 
 two - channel digital real - time oscilloscope ( tektronix tds 360 ) where the 
 kinetic curves were averaged over 256 laser pulses .
triplet lifetimes were 
 determined by exponential fitting of the kinetic curves using originpro 7.5 
 software .
unsubstituted ptbc ( 7 ) was synthesized from unmetallated phthalocyanine ( 6 ) and pbr3 in a 16.4% 
 yield , and characterized as reported in the literature [ 9 , 13 , 19 ] .
4-aminophthalonitrile 
 ( 2 ) and 4-bromophthalonitrile ( 4 ) were synthesised following literature 
 procedures [ 20 , 21 ] with some minor modifications .
4-chlorophthalonitrile ( 5 ) was synthesised by modifying the 
 procedure used for compound 4 .
4-nitrophthalonitrile(1 ) ( 1.00  g , 5.78  mmol ) was placed 
 in a round bottom flask and 100  ml of ethanol added to obtain a suspension .
the 
 catalyst pd / c ( 55  mg ) was added to the flask , the apparatus evacuated and then 
 filled with hydrogen and the mixture vigorously stirred at room temperature 
 until the absorption of hydrogen had completely stopped .
the reaction mixture 
 was subsequently filtered over celite and the solution evaporated in vacuo .
h nmr ( 400  mhz , dmso - d6 )  ppm 7.39 ( dd , j = 8.66 , 1.34  hz , 1h ) , 6.93 ( d , j = 2.19  hz , 1h ) , 6.81 ( dd , j = 8.67 , 2.18  hz , 1h ) , 6.36 ( br s , 2h ) .
compound 2 ( 500  mg , 3.5  mmol ) was taken up in 
 a mixture of water ( 4  ml ) and hydrobromic acid ( 4  ml , 48% ) and the solution 
 cooled to 0c using an ice - salt bath .
a solution of sodium nitrite 
 ( 276  mg , 4  mmol ) in water ( 2  ml ) was then added dropwise to the acid mixture to 
 form the diazonium salt 3a as an 
 intermediate . copper ( i ) bromide ( 1.00  g , 6.97  mmol ) was dissolved in hbr ( 4  ml , 48% ) and cooled to 0c .
the cold diazonium salt solution was 
 then added dropwise to the cubr reagent and the solution stirred for 1  hr at 0c 
 after an hour , the solution was left to stand at room temperature overnight .
the 
 aqueous solution was then extracted with ethyl acetate ( 3  15  ml ) , the 
 combined organic extracts washed with brine , dried over magnesium sulphate and 
 concentrated to give 248  mg of 4 .
h nmr ( 400  mhz , cdcl3 )  ppm 7.96 ( d , j 
 = 1.78  hz , 1h ) , 7.89 ( dd , j = 8.37 , 1.89  hz , 1h ) , 7.68 ( d , j = 8.37  hz , 1h ) .
c nmr ( 75  mhz , cdcl3 ) 
  ppm 136.6 ( d ) , 136.3 ( d ) , 134.4 ( d ) , 128.1 ( s ) , 117.3 ( s ) , 114.7 ( s ) , 114.5 
 ( s ) , 114.0 ( s ) . a 
 similar procedure to the one above was used to prepare compound 5 .
compound 2 ( 500  mg , 3.5  mmol ) was dissolved in a water ( 4  ml)/hydrochloric 
 acid ( 5  ml , 32% ) mixture , and the sodium nitrite ( 276  mg , 4  mmol ) in water ( 2  ml ) reagent was added to the amine hydrochloride solution to form the diazonium 
 salt ( 3b ) . copper ( i ) chloride ( 1.00 
 g , 10.1  mmol )
the 
 diazonium salt was then added to the cucl reagent and treated in the same 
 manner as reported above .
h nmr ( 400 mhz , cdcl3 )  ppm 7.80 ( d , j 
 = 1.88  hz , 1h ) , 7.75 ( s , 1h ) , 7.73 ( d , j = 1.87  hz , 1h ) .
c nmr ( 75  mhz , cdcl3 ) 
  ppm 140.2 ( s ) , 134.5 ( d ) , 133.7 ( d ) , 133.5 ( d ) , 117.4 ( s ) , 114.6 ( s ) , 114.2 
 ( s ) , 114.1 ( s ) .
complex 9 was synthesized from the 
 unmetallated derivative ( 8) . the first step was the synthesis of 8 , 
 following established methods   as follows : 4 ( 200  mg , 0.97  mmol ) was 
 reacted with dbu ( 0.36  ml ) in 1-pentanol under reflux for 12 hours under a 
 nitrogen atmosphere .
the dark green mixture was cooled down to room 
 temperature , then methanol ( 5  ml ) and water ( 2  ml ) were added and the mixture 
 precipitated out and centrifuged .
this green solid complex 8 , confirmed to be a phthalocyanine 
 molecule by its uv spectrum , was not purified any further and was 
 employed as is for the synthesis of complex 9 .
complex 9 was synthesized by heating ( under 
 reflux ) a mixture of complex 8 ( 100  mg , 0.12  mmol ) and pbr3(0.34  ml , 3.60  mmol ) in pyridine at 90 to 
 100c for 2 hours .
the reaction was then allowed to cool to room temperature 
 and poured carefully into water and allowed to stand overnight .
the green 
 product obtained was then centrifuged and washed with copious amounts of water . 
 upon drying
, the precipitate was chromatographed on a silica gel column using 
 pyridine as the eluant .
the complex was collected as a dark green band , while 
 the unmetallated pc remained at the top of the column .
uv / vis ( dmso ) , maxnm ( log ) ] : 662 ( 4.86 ) , 630 ( 4.56 ) , 602 ( 4.29 ) , 578 ( 3.79 ) , 448 
 ( 5.19 ) , 439 ( 4.94 ) , 418 ( 4.70 ) . [ ( kbr ) vmax/cm ] : 3063 , 1717 , 1608 , 1506 , 1451 , 1396 , 
 1326 , 1298 ( p = o ) , 1271 , 1151 , 1109 , 1077 , 1043 , 967 , 956 , 832 , 813 , 758 , 723 , 691 , 
 578 .
h nmr ( 600  mhz , pyr - d5 ) 
  ppm 10.159.92 ( m , 4h ) , 9.839.57 ( m , 4h ) , 8.598.41 
 ( m , 4h ) .
p nmr ( 162  mhz , pyr - d5 ) 
  ppm 198.6 . maldi
complex 11 was synthesized as 
 explained above for 9 , except that complex 5 ( 200  mg , 1.23  mmol ) was reacted with dbu ( 0.24  ml ) in 1-pentanol instead of 
 compound 4 to obtain the 4-chloro h2pc analogue ( complex 10 ) . 

the presence of the metal - free pc was again confirmed by its uv spectrum . 

complex 10 was then employed for the synthesis of complex 11 ( 100  mg , 
 0.15  mmol ) by reacting it with pbr3(0.42  ml , 4.50  mmol ) in hot 
 pyridine .
uv / vis ( dmso ) , max/nm ( log ) ] : 661 ( 4.56 ) , 630 ( 4.26 ) , 603 ( 3.99 ) , 447 ( 4.82 ) , 438 
 ( 4.59 ) , 417 ( 4.39 ) . [ ( kbr ) vmax/cm ] : 2922 , 1717 , 1609 , 1505 , 1456 , 1399 , 
 1328 , 1297 ( p = o ) , 1143 , 1068 , 973 , 910 , 814 , 769 , 724 , 690 , 580 .
h nmr ( 600  mhz , pyr - d5 )  ppm 9.979.66 ( m , 8h ) , 8.458.26 ( m , 4h ) .
682.9 , found 682.0 { cl4(tbc)p(o)}. the first step was the synthesis of metal - free complex 12 , using the same procedure as outlined above 
 for the synthesis of 8 , except that 4,5-dichlorophthalonitrile ( 300  mg 1.53  mmol ) was reacted with dbu ( 0.12  ml ) instead of complex 4 . 

confirmation of the formation of the h2pc ( 12 ) was provided by the uv spectrum .
complex 13 was then 
 synthesized as described for complexes 9 and 11 using 12 ( 100  mg , 0.128  mmol ) and pbr3 ( 0.36  ml , 3.84  mmol ) .
a paucity of proton 
 signals was expected and observed in the h nmr spectrum of this octasubstituted 
 complex .
uv / vis ( dmso ) , max/nm   ( log ) ] : 667 ( 3.47 ) , 635 ( 3.19 ) , 606 ( 2.94 ) , 452 ( 3.83 ) , 442 
 ( 3.61 ) , 422 ( 3.46 ) , 411 ( 3.42 ) .
[ ( kbr ) vmax/cm ] : 2927 , 1726 , 1586 , 1521 , 1349 , 
 1298 ( p = o ) , 1248 , 1197 , 1138 , 948 , 908 , 837 , 743 , 602 .
h nmr ( 600 mhz , pyr - d5 )  ppm 8.07 ( m , 8h ) .
maldi m / z : not observed . the 
 comparative method was used to determine the fluorescence quantum yields ( f ) according to the following 
 equation , utilizing unsubstituted znpc in dmso as the standard ( f = 0.18 ) : 
 ( 1)f=f(std  ) f  astd    2fstd    a  std2 , 
 where f and fstd 
 are the areas under the fluorescence curve of the 
 sample and the standard , respectively .
similarly , a and astd 
 are 
 the absorbance of the compound and the standard at the excitation wavelength ,  
 and std are the refractive indices of solvents used for the sample 
 and the standard , respectively .
natural or radiative 
 lifetimes ( n ) 
 were estimated using photochemcad program which uses the strickler - berg 
 equation .
the fluorescence lifetimes ( f ) were evaluated using the following equation : 
 ( 2)f=fn . 
 
the rate constants for intersystem crossing from the excited singlet state to the triplet state ( kisc(st ) ) were estimated using the following equation : 
 ( 3)kisc(st)=(1/f)(1/f0 ) , 
 where f and   f 
  are the excited 
 singlet - state lifetimes for the halogenated derivatives and unsubstituted ptbc , 
 respectively .
similarly , the rate 
 constants for intersystem crossing from the triplet state to the ground state 
 ( kisc(ts ) ) were estimated using the following equation : 
 ( 4)kisc(ts)=(1/t)(1/t0 ) , 
 where t and t0 are the excited 
 triplet - state lifetime for the halogenated derivatives and unsubstituted ptbc , 
 respectively .
solutions of the ptbc complexes were bubbled with argon in a 1  cm 
 pathlength spectrophotometric cell , irradiated at the q band of the respective ptbc complexes , with the triplet quantum yields ( t ) 
 determined by the triplet absorption method .
the comparative method   was applied 
 as in the following equation , using znpc in dmso as the standard : 
 ( 5)t=tstdat  tstdatstd  t . changes 
 in the triplet - state absorbances of the ptbc derivative and the standard are 
 represented by at and atstd , respectively ; while t and tstd are the triplet - state 
 molar extinction coefficients for the ptbc derivative and the standard , respectively ; 
 while tstd is the triplet quantum 
 yield for the standard ( t = 0.65 for znpc in dmso ) .
triplet 
 lifetimes ( t ) were determined by 
 exponential fitting of the kinetic curves using originpro 7.5 software .
quantum 
 yields of internal conversion ( ic ) were obtained from the following 
 equation , which assumes that only three processes ( fluorescence , intersystem 
 crossing , and internal conversion ) jointly deactivate the excited singlet state 
 of ptbc derivatives : 
 ( 6)ic=1(f+t ) . 

2(3 ) , 9(10 ) , 16(17 ) , 23(24)-tetrasubstituted 
 phthalocyanines can be synthesized from 4-substituted phthalonitriles , 
 while octasubstituted phthalocyanines can be synthesized from 
 4,5-dichlorophthalonitrile . in the case of tetrasubstituted derivatives , a 
 mixture of four possible structural isomers
are obtained , which can be designated 
 by their molecular symmetry as c4h , c2 , cs , and 
 d2h . 
 in 
 this study , synthesized tetrasubstituted
a variety of halogenated phosphorous 
 oxide triazatetrabenzcorroles ( complexes 9 , 11 , and 13 ) were 
 prepared by treatment of unmetallated phthalocyanines with pbr3 in 
 pyridine according to literature procedures .
the products thus obtained 
 were then subjected to silica gel column chromatography using pyridine as an 
 eluant .
generally , 
 phthalocyanine complexes are insoluble in most organic solvents ; however 
 introduction of substituents to the ring increases the solubility .
the 
 halogenated complexes ( particularly 9 and 11 ) exhibited excellent solubility in organic solvents 
 such as pyridine and dmso . for comparative purposes ,
the unsubstituted ptbc was 
 synthesized and found to be soluble in dmso , but only sparingly in pyridine .
the new 
 compounds were characterized by uv - vis , ir , mass , and nmr spectroscopies 
 ( including p nmr ) and the analyses were consistent with the 
 predicted structures as shown in section 2 . 
 however , mass spectral data proved to be difficult to obtain for complex 13 .
the p = o vibrations were observed at ~1295  cm(in accordance 
 with ) in the ir spectra , confirming the presence of o coordinated to the phosphorous 
 atom .
this was corroborated by the p nmr shifts obtained , that is , 
 ~ 198  ppm , which is typical of a p = o bond .
h nmr 
 investigations of 9 and 11 gave the characteristic 
 chemical shifts , with three proton signals integrating for a total of 12 for each 
 complex .
for complex 13 , 
 a multiplet due to the nonperipheral protons , was observed in the h 
 nmr spectrum .
tbc complexes have 
 distinct uv - vis spectra with a sharp peak at ~450  nm [ 1619 ] , which can be 
 employed in their characterization .
the 
 formation of the tbc complexes occurs when the mpc molecules no longer retains 
 a pc moiety as they no longer have the fourth azomethine nitrogen ( see schemes 1 and 2 ) . 

it is believed   that in the presence of excess metal halide , the bridge 
 nitrogen of the pc is eliminated , forming tbc . in this study
, the unmetallated pc derivatives 
 ( 8 , 
 10 and 12 ) were formed first , 
 which , upon reaction with pbr3 , resulted in the formation of ptbc 
 derivatives .
this was judged spectroscopically by the collapse of the sharp q 
 band in the visible region of unmetallated pcs to three bands ( in the q band 
 region ) , together with the formation of the sharp soret band at 440  nm ( see figure 1 ) .
the spectra of unmetallated pcs 6 , 8 , 10 , and 12 in dmso and pyridine 
 showed a single q band ( see figure 1 ) which is uncharacteristic of unmetallated 
 pcs . 
 typically , unmetallated pcs show a split q band due to lack of 
 symmetry .
solvation in polar aprotic 
 solvents ( such as dmso and pyridine ) occurs through their unshared 
 electrons .
thus , in dmso ( see figure 1 ) 
 and pyridine , the spectra of 8 , 10 , and 12 did not show the normal splitting of the q 
 band that is typical of free - base phthalocyanines , showing instead a single 
 sharp q band .
the nonsplit q band is a 
 result of the basicity of the 
 solvents .  
it has been documented that in 
 strongly basic solvents , the inner pyrrole hydrogens are acidic enough to 
 dissociate resulting in a charged system ( pc ) which becomes 
 symmetric and thus possesses an unsplit q band .
figure 2 compares the 
 spectra of the complexes synthesized in this work , while table 1 lists the q 
 and b band maxima .
it is clear in table 1 and figure 2 that the presence of 
 bromines and chlorines shifts the spectra to the red region .
the 
 red shift of spectra on halogenation has been observed before   for znpc 
 derivatives .
aggregation in 
 phthalocyanines and related complexes is usually depicted as a coplanar 
 association of rings progressing from monomer to dimer and higher - order 
 complexes .
it is dependent upon the concentration of the complex , the nature of 
 the solvent , as well as the nature of the substituents and the complexed metal 
 ions . in this study ,
the aggregation behavior of the tbc complexes ( 7 , 9 , 11 , and 13 ) was investigated in dmso ( see figure 3 ) .
the complexes did not 
 show aggregation at concentrations less than 8  10  mol dm . 

the shapes of the excitation spectra for the tbc 
 complexes were similar to the absorption spectra ( see figure 4 ) .
however , these 
 spectra were not mirror images of the fluorescence spectra for the ptbc 
 derivatives , in that the emission spectra showed only a single band , while the 
 q band of the absorption spectra has a split q band .
the observation of a single - emission 
 band in the q band region is typical of unsymmetric phthalocyanine complexes such as 
 unmetallated derivatives [ 3133 ] .
metal - free pcs are known to fluoresce with 
 only one main peak in 
 non - aqueous media which has been assigned as the 00 transition of the 
 fluorescence .
the emission spectra were slightly 
 red - shifted with stokes shifts ranging from 5 to 9  nm , suggesting no change in 
 nuclear configurations following excitation .
the largest shifts were observed for the 
 pocltbc ( 13 ) and ptbrtbc ( 9 ) , while the smallest shift was 
 observed for the ptbc derivative ( 7 ) .
the fluorescence quantum yields ( f ) of the ptbc 
 derivatives are given in table 2 .
these values are much lower than reported for 
 mpc complexes , except for the unsubstituted ptbc complex , which gives f values in the range for 
 mpc complexes .
the low values obtained for the halogenated derivatives are 
 most likely due to the heavy atom effect of the halide functional group , which 
 encourages intersystem crossing to the triplet state .
halogenation of znpc 
 has been reported to give a remarkable decrease in fluorescence quantum yields 
 and lifetimes , since incorporation of a halogen into the photosensitizer 
 increases the level spin - orbit coupling .
fluorescence lifetimes ( f , table 3 ) were calculated using 
 the strickler - berg equation .
using this 
 equation , a good correlation has been   found between 
 experimentally and theoretically determined lifetimes for the unaggregated 
 molecules as found in this work .
thus , we believe that the values obtained 
 using this equation are a good measure of fluorescence lifetimes .
halogenation 
 is expected to decrease fluorescence quantum yields and lifetimes , increase 
 triplet - state formation , and shorten triplet lifetime .
thus , as expected , the f values of the halogenated 
 derivatives were lower 
 than for unsubstituted ptbc and lower than generally observed for mpc complexes .
octasubstitution with 
 chlorines increased the f values compared to tetrasubstituted derivatives when comparing complexes 11 and 13 .
it is also interesting to note that a decrease in fluorescence 
  lifetime was observed upon contraction of the ring in tin tetrasulphonated ,,-tetrabenzcorroles 
 compared to tin tetrasulphonated phthalocyanines 
 .
the acquisition of f values allowed us to determine the 
 rate constants for various processes .
the rate constant for fluorescence ( kf ) , 
 table 3 , was highest for complex 9 , 
 which also had the lowest triplet quantum yield as will be discussed below .
likewise , 
 the rate constants for intersystem crossing from the singlet state to the 
 triplet state ( kisc ( st ) ) was the highest for complex 9 , table 3 .
the transient absorption 
 spectra were recorded in argon - degassed solutions by exciting the 
 photosensitizer ( in dmso ) in the q band region and recording the transient absorption 
 spectra point by point from 400 to 750  nm ( see figure 5 ) .
the 
 q and the soret bands showed a negative absorption ( bleaching ) and the 
 transient spectra showed a broad positive absorption ~500  nm ( see figure 5 ) .
the triplet lifetimes for 
 the ptbc derivatives , ranging from 256 to 1740 microseconds , are listed in table 2 .  
the latter value 
 was observed for the unsubstituted ptbc ( table 2 ) and it is an unusually high 
 triplet lifetime .
values in the millisecond range have been reported 
 for alpc derivatives , however they are still not as high as the value observed 
 here for unsubstituted ptbc .
the 
 presence of the halogens was expected to lower the triplet lifetimes ( when 
 compared to unhalogenated ptbc ( 7 ) ) , as 
 observed in table 2 ; with the octasubstituted complex ,   13 , giving the lowest triplet lifetime . 

contrary to the heavy atom effect , which results in the decrease in triplet lifetimes 
 with an increase in the size of the halogen , this work shows an increase 
 in lifetime on going from the chlorinated ( 11 ) 
 to brominated ( 9 ) ptbc derivatives , with 
 the octachlorinated ( 13 ) complex showing 
 the lowest triplet lifetime .
the latter 
 ( 13 ) could have a lower triplet 
 lifetime than the tetrachlorinated derivative ( 11 ) 
 due to the plurality of chlorine atoms and the heavy atom effect .
we have recently 
 shown that upon contraction of the ring in tin tetrasulphonated ,,-tetrabenzcorrole compared to tin tetrasulphonated 
 phthalocyanine , there was a decrease in t values and the triplet lifetimes . 

however , the lifetimes reported here for ptbc derivatives are high compared to 
 mpc complexes in general . in general , there is an 
 increase in t values upon halogenation with a striking exception of the brominated complex   ( 9 ) .
the octachlorinated derivatives ( 13 ) gave the highest triplet quantum 
 yield ( t ) , 
 while surprisingly the bromo substituted 
 complex 9 gave the lowest value .
the t value for 9 is almost ten - fold lower 
 than for 11 .
again , the larger value of t for 13 could be due to the plurality of chlorines and the heavy atom 
 effect .
the low t value for the brominated 
 derivative compared to the chlorinated one contradicts the heavy atom effect .
the 
 increased t value for the chlorinated derivatives 11 and 13 compared to 9 will result in shorter triplet 
 lifetime for the former , and this is the case in table 2 .
quantum yields of 
 internal conversion ( ic ) 
 were calculated using ( 6 ) and are high 
 due to low t values .
using the triplet lifetimes , the rate constants for intersystem 
 crossing from the triplet state to the ground state ( kisc ( ts ) ) were 
 determined and are shown in table 3 .
the lowest ( kisc ( ts ) ) value obtained is for complex 9   ( table 3 ) yet this complex has the 
 lowest triplet quantum yield .
in conclusion , we have 
 synthesized halogenated ptbc derivatives ( complexes 9 , 11 , and 13 ) and 
 compared their photophysical data with that of the unsubstituted ptbc complex . 
 the latter complex shows a very high triplet lifetime value , higher than that for 
 mpc complexes .
complexes 11 and 13 show reasonably 
 high triplet lifetimes and yields , making them possible candidates for pdt .
complex 9 having bromine substituents showed 
 a behavior different from the other halogenated complexes ( 11 and 13 ) in that it 
 gave a very low triplet quantum yield .
 the synthesis of phosphorous oxide triazatetrabenzcorroles ( tbc ) tetra- ( 9 , 11 ) or octa- ( 13 ) 
     substituted on the ring with halogenated functional groups is reported . 
 the complexes are not aggregated 
      in dimethylsulfoxide ( dmso ) and show solubility in solvents such as pyridine . the q 
  band absorption spectra 
       of the complexes are red - shifted compared to unsubstituted ptbc . 
 the latter complex shows a large triplet 
        lifetime ( 1.7  milliseconds ) , higher than for mpc derivatives . 
 the chlorinated derivatives show good triplet 
         yields ( t 0.46 and 0.36 ) and relatively long lifetimes ( 256 and 452 microseconds ) , respectively , for 11 and 13 . 
1. INTRODUCTION
2. EXPERIMENTAL PROCEDURES
3. RESULTS AND DISCUSSION
4. CONCLUSIONS