Superexchange Contributions to Distance Dependence of Electron Transfer/Transport: Exchange and Electronic Coupling in Oligo(para-Phenylene)- and Oligo(2,5-Thiophene)-Bridged Donor鈥揃ridge鈥揂ccep

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• 作者：Martin L. Kirk ; David A. Shultz ; Daniel E. Stasiw ; Geoffrey F. Lewis ; Guangbin Wang ; Candice L. Brannen ; Roger D. Sommer ; Paul D. Boyle
• 刊名：Journal of the American Chemical Society
• 出版年：2013
• 出版时间：November 13, 2013
• 年：2013
• 卷：135
• 期：45
• 页码：17144-17154
• 全文大小：641K
• 年卷期：v.135,no.45(November 13, 2013)
• ISSN：1520-5126

文摘

The preparation and characterization of three new donor鈥揵ridge鈥揳cceptor biradical complexes are described. Using variable-temperature magnetic susceptibility, EPR hyperfine coupling constants, and the results of X-ray crystal structures, we evaluate both exchange and electronic couplings as a function of bridge length for two quintessential molecular bridges: oligo(para-phenylene), 尾 = 0.39 脜^鈥? and oligo(2,5-thiophene), 尾 = 0.22 脜^鈥?. This report represents the first direct comparison of exchange/electronic couplings and distance attenuation parameters (尾) for these bridges. The work provides a direct measurement of superexchange contributions to 尾, with no contribution from incoherent hopping. The different 尾 values determined for oligo(para-phenylene) and oligo(2,5-thiophene) are due primarily to the D鈥揃 energy gap, 螖, rather than bridge鈥揵ridge electronic couplings, H_BB. This is supported by the fact that the H_BB values extracted from the experimental data for oligo(para-phenylene) (H_BB = 11鈥?00 cm^鈥?) and oligo(2,5-thiophene) (12鈥?00 cm^鈥?) differ by <10%. The results presented here offer unique insight into the intrinsic molecular factors that govern H_DA and 尾, which are important for understanding the electronic origin of electron transfer and electron transport mediated by molecular bridges.