Vibrational Radiationless Transition from Triplet States of Chromophores at Room Temperature.

The radiationless transition rate based on intramolecular vibrations from the lowest excited triplet state (T1) at room temperature [knr(RT)] is crucial for triplet energy harvesting in optoelectronics and photonics applications. Although a decrease of knr(RT) of chromophores with strong intermolecular interactions is often proposed, scientific evidence for this has not been reported. Here we report a method to predict knr(RT). We optically estimated knr(RT) of various molecularly dispersed chromophores with a variety of transition characteristics from T1 to the ground state (S0) under appropriate inert liquid or solid host conditions. Spin-orbit coupling (SOC) without considering molecular vibrations was not correlated with the estimated knr(RT). However, the estimated knr(RT) was strongly correlated with a multiplication of SOC considering vibrations freely allowed at room temperature and the Franck-Condon factor. This correlation revealed that knr(RT) of many heavy-atom-free chromophores with a visible T1-S0 transition energy and local excited T1-S0 transition characteristics is intrinsically less than 100 s-1 even when vibrations freely occur. This information will assist researchers to appropriately design materials without limitations regarding intermolecular interactions to control T1 lifetime at room temperature and facilitate triplet energy harvesting.