报告题目：Excited States Control of Organic Luminescent Molecules: Inverted Singlet and Triplet Excited State

报告人：
Yong-Jin Pu 日本理化学研究所（RIKEN）

报告时间：2023年10月10日 星期二 15.30-17:30

地点：光电所三楼会议室

邀请人：郝晓涛 教授

摘要：Control of excited states of organic luminescent molecules has been fundamentally important in their light-related applications such as LEDs, solar cells, sensors, photocatalysts, etc. When neutral and closed-shell organic molecules are optically or electrically excited, spin multiplicity of the excited state will be either singlet or triplet. In general, without any heavy atoms, the singlet excited state is bright and the triplet excited state is dark because of a spin selection rule. Therefore, reverse intersystem crossing from triplet excited states to singlet excited states makes light emission efficient. Energetically low and long-lived triplet excited states are involved in unique photophysical characteristics: singlet exciton fission, triplet–triplet annihilation, delayed fluorescence, etc. We designed and synthesized the organic luminescent molecules showing unique triplet excited states–related phenomena [1–4].

In molecular excited states, an energy gap between singlet (S₁) and triplet (T₁) excited states is positive, i.e. energy level of S₁ is higher than that of T₁. It is because of exchange energy of the two electrons in the excited state. However, here, we report fluorescent molecules that have a negative S₁– T₁ energy gap of –11 ± 2 meV [4]. The energy inversion of the S₁ and T₁ excited states results in delayed fluorescence with short time constants of 0.2 μs, which anomalously decrease with decreasing temperature owing to the emissive singlet character of the lowest-energy excited state. OLEDs using this molecule exhibited a fast transient electroluminescence decay with a peak external quantum efficiency of 17%, demonstrating its potential implications for optoelectronic devices, including displays, lighting, and lasers.

简历：Yong-Jin Pu教授现任日本理化学研究所新兴物质科学中心，超分子功能化学部新兴超分子材料组组长。2002年获得早稻田大学应用化学博士学位；2004年获日本学术振兴会“海外特别研究员”称号；2006年担任山形大学工学部高分子機能工学科助教；2013年担任日本科学技术振兴机构 PRESTO 研究员；主要研究方向包括：有机光电器件激发态物理；半导体纳米粒子;胶体量子点材料研究；高效有机太阳能电池；有机半导体分子和无机半导体粒子的结构、组成和聚集状态（动态/静态）控制等。