the C13b position. In addition, this band is only slightly sensitive to changes to the central metal ion (compounds B and C) or the C17 carboxylic acid (compound D) but removal of the C13a=O group (compound F) downshifts the C13b ester band by ~8 cm-1, confirming that it is coupled to other vibrational modes in the ring E. Although these groups are the most intense IR markers in this region, due to their close proximity to the conjugated electronic macrocycle, the in-plane porphyrin ring vibrations in the 1500-1600 cm-1 region are influenced by alterations to the central metal ion. The C17 carboxylic acid group is located further away from the main macrocycle and therefore, changing this group to a methylester (compound D) only has a minor effect on the IR difference spectrum upon electronic excitation. Figure 6. Fitting of EADS1 from the global analysis of the transient IR absorption data for Pchlide derivatives to a sum of Gaussian functions. The EADS (black dots) have been fitted A-F with a sum (black line) of Gaussian functions (negative shown as blue lines, positive as red lines). Positions and FWHM (in brackets) are indicated. Peaks can be assigned to the C13a carbonyl (1569-1706 cm-1), C13b methylester (1730-1754 cm-1) and C=C of delocalized porphyrin skeleton modes (below 1572 cm-1). DFT frequency calculations of ground and excited state structures in the gas phase confirm the experimental assignments, as described in the supplementary information. The excited state frequency calculations can be subtracted from those calculated in the ground state to generate difference spectra, which confirm that the major signals arise from the ring E C=O groups (Figure S30). The two major vibrations at 1814 and 1805 cm-1 correspond to coupled vibrations from the C13b ester and C13a=O carbonyl groups, respectively, whereas all features at lower
the C13b position. In addition, this band is only slightly sensitive to changes to the central metal ion (compounds B and C) or the C17 carboxylic acid (compound D) but removal of the C13a=O group (compound F) downshifts the C13b ester band by ~8 cm-1, confirming that it is coupled to other vibrational modes in the ring E. Although these groups are the most intense IR markers in this region, due to their close proximity to the conjugated electronic macrocycle, the in-plane porphyrin ring vibrations in the 1500-1600 cm-1 region are influenced by alterations to the central metal ion. The C17 carboxylic acid group is located further away from the main macrocycle and therefore, changing this group to a methylester (compound D) only has a minor effect on the IR difference spectrum upon electronic excitation. Figure 6. Fitting of EADS1 from the global analysis of the transient IR absorption data for Pchlide derivatives A-F to a sum of Gaussian functions. The EADS (black dots) have been fitted with a sum (black line) of Gaussian functions (negative shown as blue lines, positive as red lines). Positions and FWHM (in brackets) are indicated. Peaks can be assigned to the C13a carbonyl (1569-1706 cm-1), C13b methylester (1730-1754 cm-1) and C=C of delocalized porphyrin skeleton modes (below 1572 cm-1). DFT frequency calculations of ground and excited state structures in the gas phase confirm the experimental assignments, as described in the supplementary information. The excited state frequency calculations can be subtracted from those calculated in the ground state to generate difference spectra, which confirm that the major signals arise from the ring E C=O groups (Figure S30). The two major vibrations at 1814 and 1805 cm-1 correspond to coupled vibrations from the C13b ester and C13a=O carbonyl groups, respectively, whereas all features at lower
51342879.Pchlide_analogues_photochemistry_JPCB.docx