Large Acceleration Effect of Photoinduced Electron Transfer in Porphyrin-Quinone Dyads with a Rigid Spacer Involving a Dihalosubstituted Three-Membered Ring

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• 作者：Hirohito Tsue ; Hiroshi Imahori ; Takahiro Kaneda ; Yoshinori Tanaka ; Tadashi Okada ; Koichi Tamaki ; and Yoshiteru Sakata
• 刊名：Journal of the American Chemical Society
• 出版年：2000
• 出版时间：March 15, 2000
• 年：2000
• 卷：122
• 期：10
• 页码：2279 - 2288
• 全文大小：239K
• 年卷期：v.122,no.10(March 15, 2000)
• ISSN：1520-5126

文摘

To understand the contribution of spacer structure toward electron transfer (ET) and to regulateelectronic coupling between a redox pair, porphyrin-spacer-benzoquinone molecules were prepared wherespacers are trans-decalin and dihalosubstituted tricyclo[4.4.1.0]undecane including a three-membered ring.These compounds were designed to have almost the same separation distance between a redox pair, the samenumber of intervening bonds, and the nearly equal free energy change associated with the ET reaction. TheET rates for the charge separation process were evaluated on the basis of the fluorescence lifetimes. A quitelarge difference in the ET rates was observed among these compounds, and the ET rates for the compoundshaving the three-membered rings were ca. 50 to 60 times larger than that with trans-decalin spacer in THF.From the analysis of temperature dependence of the ET rates, it was shown that the observed rate accelerationis caused by both an increase of the electronic coupling and a decrease of the reorganization energy. Ab initiocalculations of the electronic coupling elements and on molecular orbitals for the cyclopropanes predicted thatthe former may be due to the enhancement of the ET pathways arising from the bent geometry of the spaceror of the mixing pathway induced by a very low lying antibonding orbital in the dihalosubstituted cyclopropane.