Muthiah Chinnasamy, Kee Hooi Ling, Diers James R, Fan Dazhong, Ptaszek Marcin, Bocian David F, Holten Dewey, Lindsey Jonathan S
Department of Chemistry, North Carolina State University, Raleigh, NC, USA.
Photochem Photobiol. 2008 May-Jun;84(3):786-801. doi: 10.1111/j.1751-1097.2007.00258.x. Epub 2008 Jan 15.
Understanding energy transfer among hydroporphyrins is of fundamental interest and essential for a wide variety of photochemical applications. Toward this goal, a synthetic free base ethynylphenylchlorin has been coupled with a synthetic free base bromobacteriochlorin to give a phenylethyne-linked chlorin-bacteriochlorin dyad (FbC-pe-FbB). The chlorin and bacteriochlorin are each stable toward adventitious oxidation because of the presence of a geminal dimethyl group in each reduced pyrrole ring. A combination of static and transient optical spectroscopic studies indicate that excitation into the Qy band of the chlorin constituent (675 nm) of FbC-pe-FbB in toluene results in rapid energy transfer to the bacteriochlorin constituent with a rate of approximately (5 ps)(-1) and efficiency of >99%. The excited bacteriochlorin resulting from the energy-transfer process in FbC-pe-FbB has essentially the same fluorescence characteristics as an isolated monomeric reference compound, namely a narrow (12 nm fwhm) fluorescence emission band at 760 nm and a long-lived (5.4 ns) Qy excited state that exhibits a significant fluorescence quantum yield (Phif=0.19). Förster calculations are consistent with energy transfer in FbC-pe-FbB occurring predominantly by a through-space mechanism. The energy-transfer characteristics of FbC-pe-FbB are compared with those previously obtained for analogous phenylethyne-linked dyads consisting of two porphyrins or two oxochlorins. The comparisons among the sets of dyads are facilitated by density functional theory calculations that elucidate the molecular-orbital characteristics of the energy donor and acceptor constituents. The electron-density distributions in the frontier molecular orbitals provide insights into the through-bond electronic interactions that can also contribute to the energy-transfer process in the different types of dyads.
了解氢卟啉之间的能量转移具有重要的基础意义，并且对于多种光化学应用至关重要。为了实现这一目标，一种合成的游离碱乙炔基苯基二氢卟酚与一种合成的游离碱溴细菌叶绿素相结合，得到了一种苯基乙炔连接的二氢卟酚-细菌叶绿素二元体（FbC-pe-FbB）。由于每个还原的吡咯环中都存在偕二甲基，二氢卟酚和细菌叶绿素对偶然氧化均具有稳定性。静态和瞬态光谱学研究表明，在甲苯中，FbC-pe-FbB的二氢卟酚成分（675 nm）的Qy带被激发后，会迅速将能量转移到细菌叶绿素成分，转移速率约为(5 ps)(-1)，效率大于99%。由FbC-pe-FbB中的能量转移过程产生的激发态细菌叶绿素具有与分离的单体参考化合物基本相同的荧光特性，即在760 nm处有一个窄的（半高宽12 nm）荧光发射带，以及一个长寿命的（5.4 ns）Qy激发态，其荧光量子产率显著（Phif = 0.19）。福斯特计算结果与FbC-pe-FbB中的能量转移主要通过空间机制发生相一致。将FbC-pe-FbB的能量转移特性与先前获得的由两个卟啉或两个氧代二氢卟酚组成的类似苯基乙炔连接二元体的特性进行了比较。密度泛函理论计算有助于对二元体系进行比较，该计算阐明了能量供体和受体成分的分子轨道特性。前沿分子轨道中的电子密度分布为通过键的电子相互作用提供了见解，这种相互作用也可能对不同类型二元体中的能量转移过程有贡献。
