Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 132, Issue 43, Pages 15427-15434Publisher
AMER CHEMICAL SOC
DOI: 10.1021/ja107420a
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- Chemical Sciences, Geosciences, and Biosciences Division, Office of Basic Energy Sciences, DOE [DE-FG02-99ER14999]
- NSF Chemistry Division
- Link Foundation
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Photoinitiated charge separation (CS) and recombination (CR) in a series of donor-bridge-acceptor (D-B-A) molecules with cross-conjugated, linearly conjugated, and saturated bridges have been compared and contrasted using time-resolved spectroscopy. The photoexcited charge transfer state of 3,5-dimethyl-4-(9-anthracenyl)julolidine (DMJ-An) is the donor, and naphthalene-1,8:4,5-bis(dicarboximide) (NI) is the acceptor in all cases, along with 1,1-diphenylethene, trans-stilbene, diphenylmethane, and xanthone bridges. Photoinitiated CS through the cross-conjugated 1,1-diphenylethene bridge is about 30 times slower than through its linearly conjugated trans-stilbene counterpart and is comparable to that observed through the diphenylmethane bridge. This result implies that cross-conjugation strongly decreases the pi orbital contribution to the donor-acceptor electronic coupling so that electron transfer most likely uses the bridge a system as its primary CS pathway. In contrast, the CS rate through the cross-conjugated xanthone bridge is comparable to that observed through the linearly conjugated trans-stilbene bridge. Molecular conductance calculations on these bridges show that cross-conjugation results in quantum interference effects that greatly alter the through-bridge donor-acceptor electronic coupling as a function of charge injection energy. These calculations display trends that agree well with the observed trends in the electron transfer rates.
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