TY - JOUR
T1 - Structural effects on photoinduced electron transfer in carotenoid-porphyrin-quinone triads
AU - Kuciauskas, Darius
AU - Liddell, Paul A.
AU - Hung, Su Chun
AU - Lin, Su
AU - Stone, Simon
AU - Seely, Gilbert R.
AU - Moore, Ana L.
AU - Moore, Thomas A.
AU - Gust, Devens
PY - 1997/1/16
Y1 - 1997/1/16
N2 - meso-Polyarylporphyrins are often used as components of molecules that mimic photosynthetic reaction centers by carrying out photoinduced electron-transfer reactions. Studies of these systems have raised questions concerning the role of alkyl substituents at the "β-pyrrolic" positions on the porphyrin periphery in limiting π-π overlap between the macrocycle and the aryl rings. The degree of overlap affects electronic coupling and, therefore, the rates of electron-transfer reactions. There is also evidence that when the linkages joining porphyrins to electron-acceptor or -donor moieties contain amide bonds, the sense of the amide linkage may strongly affect electron-transfer rate constants. In this study, three carotenoid-porphyrin-quinone molecular triads and various model compounds have been prepared, and electron-transfer has been studied using time-resolved emission and absorption techniques. The results show that steric hindrance due to methyl groups at the β-pyrrolic positions reduces electron-transfer rate constants by a factor of ∼1/5. In addition, amide-containing donor-acceptor linkages having the nitrogen atom attached to the porphyrin meso-aryl ring demonstrate electron-transfer rate constants ∼30 times larger than those for similar linkages with the amide reversed, after correction for thermodynamic effects.
AB - meso-Polyarylporphyrins are often used as components of molecules that mimic photosynthetic reaction centers by carrying out photoinduced electron-transfer reactions. Studies of these systems have raised questions concerning the role of alkyl substituents at the "β-pyrrolic" positions on the porphyrin periphery in limiting π-π overlap between the macrocycle and the aryl rings. The degree of overlap affects electronic coupling and, therefore, the rates of electron-transfer reactions. There is also evidence that when the linkages joining porphyrins to electron-acceptor or -donor moieties contain amide bonds, the sense of the amide linkage may strongly affect electron-transfer rate constants. In this study, three carotenoid-porphyrin-quinone molecular triads and various model compounds have been prepared, and electron-transfer has been studied using time-resolved emission and absorption techniques. The results show that steric hindrance due to methyl groups at the β-pyrrolic positions reduces electron-transfer rate constants by a factor of ∼1/5. In addition, amide-containing donor-acceptor linkages having the nitrogen atom attached to the porphyrin meso-aryl ring demonstrate electron-transfer rate constants ∼30 times larger than those for similar linkages with the amide reversed, after correction for thermodynamic effects.
UR - http://www.scopus.com/inward/record.url?scp=0030783550&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0030783550&partnerID=8YFLogxK
U2 - 10.1021/jp962210x
DO - 10.1021/jp962210x
M3 - Article
AN - SCOPUS:0030783550
VL - 101
SP - 429
EP - 440
JO - Journal of Physical Chemistry B
JF - Journal of Physical Chemistry B
SN - 1520-6106
IS - 3
ER -