TY - JOUR
T1 - Effects of substituents on synthetic analogs of chlorophylls. Part 3
T2 - The distinctive impact of auxochromes at the 7- versus 3-positions
AU - Springer, Joseph W.
AU - Faries, Kaitlyn M.
AU - Diers, James R.
AU - Muthiah, Chinnasamy
AU - Mass, Olga
AU - Kee, Hooi Ling
AU - Kirmaier, Christine
AU - Lindsey, Jonathan S.
AU - Bocian, David F.
AU - Holten, Dewey
PY - 2012/5
Y1 - 2012/5
N2 - Assessing the effects of substituents on the spectra of chlorophylls is essential for gaining a deep understanding of photosynthetic processes. Chlorophyll a and b differ solely in the nature of the 7-substituent (methyl versus formyl), whereas chlorophyll a and d differ solely in the 3-substituent (vinyl versus formyl), yet have distinct long-wavelength absorption maxima: 665 (a) 646 (b) and 692 nm (d). Herein, the spectra, singlet excited-state decay characteristics, and results from DFT calculations are examined for synthetic chlorins and 13 1-oxophorbines that contain ethynyl, acetyl, formyl and other groups at the 3-, 7- and/or 13-positions. Substituent effects on the absorption spectra are well accounted for using Gouterman's four-orbital model. Key findings are that () the dramatic difference in auxochromic effects of a given substituent at the 7- versus3- or 13-positions primarily derives from relative effects on the LUMO+1 and LUMO; (2) formyl at the 7- or 8-position effectively "porphyrinizes" the chlorin and (3) the substituent effect increases in the order of vinyl < ethynyl < acetyl < formyl. Thus, the spectral properties are governed by an intricate interplay of electronic effects of substituents at particular sites on the four frontier MOs of the chlorin macrocycle. Chlorophyll a and b differ solely in the nature of the 7-substituent, whereas chlorophyll a and d differ solely in the 3-substituent, yet have distinct long-wavelength absorption maxima: 665 (a) 646 (b) and 692 nm (d). Herein, the spectra, singlet excited-state decay characteristics, and results from DFT calculations are examined for synthetic chlorins and 13 1-oxophorbines that contain a variety of substituents at the 3-, 7- and/or 13-positions. An intricate interplay of site-specific electronic effects of substituents on the four frontier MOs of the chlorin macrocycle is found to govern the spectral properties.
AB - Assessing the effects of substituents on the spectra of chlorophylls is essential for gaining a deep understanding of photosynthetic processes. Chlorophyll a and b differ solely in the nature of the 7-substituent (methyl versus formyl), whereas chlorophyll a and d differ solely in the 3-substituent (vinyl versus formyl), yet have distinct long-wavelength absorption maxima: 665 (a) 646 (b) and 692 nm (d). Herein, the spectra, singlet excited-state decay characteristics, and results from DFT calculations are examined for synthetic chlorins and 13 1-oxophorbines that contain ethynyl, acetyl, formyl and other groups at the 3-, 7- and/or 13-positions. Substituent effects on the absorption spectra are well accounted for using Gouterman's four-orbital model. Key findings are that () the dramatic difference in auxochromic effects of a given substituent at the 7- versus3- or 13-positions primarily derives from relative effects on the LUMO+1 and LUMO; (2) formyl at the 7- or 8-position effectively "porphyrinizes" the chlorin and (3) the substituent effect increases in the order of vinyl < ethynyl < acetyl < formyl. Thus, the spectral properties are governed by an intricate interplay of electronic effects of substituents at particular sites on the four frontier MOs of the chlorin macrocycle. Chlorophyll a and b differ solely in the nature of the 7-substituent, whereas chlorophyll a and d differ solely in the 3-substituent, yet have distinct long-wavelength absorption maxima: 665 (a) 646 (b) and 692 nm (d). Herein, the spectra, singlet excited-state decay characteristics, and results from DFT calculations are examined for synthetic chlorins and 13 1-oxophorbines that contain a variety of substituents at the 3-, 7- and/or 13-positions. An intricate interplay of site-specific electronic effects of substituents on the four frontier MOs of the chlorin macrocycle is found to govern the spectral properties.
UR - http://www.scopus.com/inward/record.url?scp=84860661705&partnerID=8YFLogxK
U2 - 10.1111/j.1751-1097.2012.01083.x
DO - 10.1111/j.1751-1097.2012.01083.x
M3 - Article
C2 - 22248176
AN - SCOPUS:84860661705
SN - 0031-8655
VL - 88
SP - 651
EP - 674
JO - Photochemistry and Photobiology
JF - Photochemistry and Photobiology
IS - 3
ER -