Organic gain materials are highly attractive for lasing due to their chemical tunability and large stimulated emission cross sections. In previous reports, the radiative decay rate k_r was considered as an important factor to determine outstanding amplified spontaneous emission (ASE) performance of organic molecules. In this study, we use quantum mechanics to reveal the influential factors on photophysical properties of organic emitters, and give insight into the effect of k_r on ASE performance. Based on the theoretical analysis of three molecules with similar structure, calculated results show that large k_r derives from enhanced transition density ρ between the electronic wave functions of the ground-state and the lowest excited singlet state as well as a handful of low-frequency torsional modes with small Huang–Rhys factor S, further, k_r values are calculated depending on molecular vibration terms. In addition, through the analysis of non-radiative decay rate k_nr considering vibration terms (vibronic coupling constants), the comparison of k_r and k_nr shows that the radiative decay process is promoted in the three molecules. The two aspects are desired for outstanding ASE performance. Our work shows that the roles of transition density and vibrational modes are crucial to clarify the photophysical properties, which govern the ASE performance in organic light emitters.

中文翻译：

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有机发射器中低阈值放大的自发发射的理论证据：跃迁密度和分子内振动模式分析

有机增益材料因其化学可调性和受激发射截面大而对激光具有极强的吸引力。在以前的报告中，辐射衰减率k _r被认为是确定有机分子出色的放大自发发射（ASE）性能的重要因素。在这项研究中，我们使用量子力学揭示了影响有机发射体光物理性质的因素，并深入了解了k _r对ASE性能的影响。基于对具有相似结构的三个分子的理论分析，计算结果表明，较大的k _r来自增强的跃迁密度ρ在基态和最低激发单重态的电子波函数之间，以及在少数具有较小Huang-Rhys因子S的低频扭转模的电子波函数之间，进一步根据分子振动项计算k _r值。另外，通过考虑振动项（振动耦合常数）的非辐射衰减率k _nr的分析，比较k _r和k _nr表明在三个分子中促进了辐射衰减过程。这两个方面是出色的ASE性能所需要的。我们的工作表明，转变密度和振动模式的作用对于阐明光物理特性至关重要，光物理特性决定了有机发光体中ASE的性能。