School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram , CET Campus, Sreekaryam, Thiruvananthapuram, Kerala, India 695016.
J Am Chem Soc. 2015 Dec 23;137(50):15604-7. doi: 10.1021/jacs.5b08257. Epub 2015 Oct 14.
We report a nonparallel stacked arrangement of donor–acceptor (D–A) pairs for prolonging the lifetime of photoinduced charge-separated states. Hydrogen–hydrogen steric repulsion in naphthalimide-naphthalene (NIN) dyad destabilizes the planar geometry between the constituent units in solution/ground state. Sterically imposed nonplanar geometry of the dyad allows the access of nonparallel arrangement of the donor and acceptor stacks having triclinic space group in the crystalline state. Antiparallel trajectory of excitons in nonparallel D–A stacks can result in lower probability of geminate charge recombination, upon photoexcitation, thereby resulting in a long-lived charge-separated state. Upon photoexcitation of the NIN dyad, electron transfer from naphthalene to the singlet excited state of naphthalimide moiety results in radical ion pair intermediates that survive >10,000-fold longer in the aggregated state (τcra > 1.2 ns) as compared to that of monomeric dyad (τcrm < 110 fs), monitored using femtosecond transient absorption spectroscopy.
我们报告了一种非平行堆叠的给体-受体（D-A）对排列，以延长光致电荷分离态的寿命。在萘酰亚胺-萘（NIN）二联体中，氢-氢位阻使组成单元在溶液/基态中的平面几何结构不稳定。二联体施加的空间位阻迫使非平面几何结构允许供体和受体堆叠以三斜空间群的形式在晶体状态下进行非平行排列。在非平行 D-A 堆叠中激子的反平行轨迹可能导致光激发后孪生电荷复合的概率降低，从而产生长寿命的电荷分离态。在 NIN 二联体的光激发下，从萘向萘酰亚胺部分的单重激发态的电子转移导致自由基离子对中间体的生成，与单体二联体（τcrm < 110 fs）相比，在聚集态下的寿命延长了 >10,000 倍（τcra > 1.2 ns），这是使用飞秒瞬态吸收光谱监测到的。
