Department of Chemistry and Pharmacy & Interdisciplinary Center for Molecular Materials , Friedrich-Alexander-Universität Erlangen Nürnberg , Egerlandstr. 3 , 91058 Erlangen , Germany.
Department of Chemistry and Pharmacy & Interdisciplinary Center for Molecular Materials , Friedrich-Alexander-Universität Erlangen Nürnberg , Nikolaus-Fiebiger-Str. 10 , 91058 Erlangen , Germany.
J Am Chem Soc. 2019 Apr 17;141(15):6191-6203. doi: 10.1021/jacs.8b09510. Epub 2019 Apr 9.
We have designed and used four different spacers, denoted A-D, to connect two pentacenes and to probe the impact of intramolecular forces on the modulation of pentacene-pentacene interactions and, in turn, on the key steps in singlet fission (SF), that is, the (SS)-to-(TT) as well as (TT)-to-(TT) transitions by means of transient absorption and electron paramagnetic resonance measurements. In terms of the (SS)-to-(TT) transition, a superexchange mechanism, that is, coupling to a higher-lying CT state to generate a virtual intermediate, enables rapid SF in A-D. Sizeable electronic coupling in A and B opens, on one hand, an additional pathway, that is, the population of a real intermediate, and changes, on the other hand, the mechanism to that of hopping. In turn, A and B feature much higher (TT) quantum yields than C and D, with a maximum value of 162% for A. In terms of the (TT)-to-(TT) transition, the sizable electronic coupling in A and B is counterproductive, and C and D give rise to higher (TT)-to-(T + T) quantum yields than A and B, with a maximum value of 85% for D.
我们设计并使用了四种不同的间隔物 A-D，将两个并五苯连接起来，并通过瞬态吸收和电子顺磁共振测量来探测分子内力对并五苯-并五苯相互作用的调制以及对单态裂变 (SF) 的关键步骤的影响，即 (SS)-到-(TT) 以及 (TT)-到-(TT) 跃迁。对于 (SS)-到-(TT) 跃迁，超交换机制，即与较高的 CT 态耦合以产生虚拟中间态，使得 A-D 中的 SF 迅速发生。A 和 B 中的可观的电子偶联一方面打开了另一个途径，即真实中间态的布居，另一方面改变了机制为跳跃机制。反过来，A 和 B 的 (TT) 量子产率比 C 和 D 高得多，A 的最大值为 162%。对于 (TT)-到-(TT) 跃迁，A 和 B 中的可观的电子偶联是适得其反的，而 C 和 D 导致比 A 和 B 更高的 (TT)-到-(T+T) 量子产率，D 的最大值为 85%。
