Abstract

 Three polycyclic chromeno[2,3-b]indolecontaining indole and naphthalene rings fused by a pyran ring were synthesized by metal-free C–H functionalization method and their photophysical studies were done. Steady state absorption spectra do not show solvent effect while fluorescence spectra exhibit solvatochromic shift. The molecules exhibit ultra-high Stokes shift of the order of 3.07 eV (24,696 cm⁻¹) in acetonitrile and 2.12 eV (17,054 cm⁻¹) in ethyl acetate. To corroborate experimental observation, we performed computational investigation both in gas and solvent phases. The computed results are in good agreement with the experimental observation. Analysis of the frontier molecular orbitals as well as natural transition orbitals depicts intramolecular charge transfer in the molecules. Further, gas phase as well as solvent phases optimized structures in the ground and excited states of all chosen molecules show increase in planarity in the excited state. An excited state intramolecular charge transfer accompanied by structural relaxation leading to planarity in the excited state has been suggested to cause large Stokes shifted fluorescence emission in these molecules.

摘要

采用无金属C-H官能化方法合成了三个由吡喃环稠合的含吲哚和萘环的 多环色烯[2,3 -b ]吲哚并进行了光物理研究。稳态吸收光谱不显示溶剂效应，而荧光光谱显示溶剂变色位移。^{分子在乙腈中表现出 3.07 eV (24,696 cm -1} ) 和 2.12 eV (17,054 cm ^-1 )量级的超高斯托克斯位移) 在乙酸乙酯中。为了证实实验观察，我们在气相和溶剂相中进行了计算研究。计算结果与实验观察吻合较好。前沿分子轨道以及自然跃迁轨道的分析描绘了分子中的分子内电荷转移。此外，所有选择的分子的基态和激发态中的气相和溶剂相优化结构显示激发态的平面度增加。已经提出激发态分子内电荷转移伴随结构弛豫导致激发态平面性导致这些分子中的大斯托克斯位移荧光发射。