Liu Ran, Gao Xing, Barbatti Mario, Jiang Jun, Zhang Guozhen
Hefei National Laboratory for Physical Sciences at the Microscale, iChEM (Collaborative Innovation Center of Chemistry for Energy Materials), School of Chemistry and Materials Science , University of Science and Technology of China , Hefei , Anhui 230026 , P. R. China.
Department of Chemistry , 930 N University Ave, University of Michigan , Ann Arbor , Michigan 48109 , United States.
J Phys Chem Lett. 2019 Mar 21;10(6):1388-1393. doi: 10.1021/acs.jpclett.9b00286. Epub 2019 Mar 11.
Pure light-atom organic phosphorescent molecules have been under scientific scrutiny because they are inexpensive, flexible, and environment friendly. The development of such materials, however, faces a bottleneck problem of intrinsically small spin-orbit couplings, which can be addressed by seeking a proper balance between intersystem crossing (ISC) and fluorescence rates. Using N-substituted naphthalimides as the prototype molecule, we applied chemical modifications with several electrophilic and nucleophilic functional groups, to approach the goal. The selected electron donating groups actively restrain the fluorescence, enabling an efficient ISC to the triplet manifold. Electron withdrawing groups do not change the luminescent properties of the parent species. The changes in ISC and fluorescence rates are related to the nature of the lowest singlet state, which changes from localized excitation into charge-transfer excitation upon configuration change of excited molecules. This finding opens an alternative strategy for designing pure light-atom organic phosphorescent molecules for emerging luminescent materials applications.
纯轻原子有机磷光分子一直受到科学关注，因为它们价格低廉、具有灵活性且环境友好。然而，这类材料的发展面临着一个内在自旋 - 轨道耦合较小的瓶颈问题，这可以通过在系间窜越（ISC）和荧光速率之间寻求适当平衡来解决。我们以 N - 取代萘二甲酰亚胺作为原型分子，应用了几种亲电和亲核官能团进行化学修饰，以实现这一目标。所选的供电子基团有效地抑制了荧光，使得能够高效地系间窜越到三重态。吸电子基团不会改变母体物种的发光特性。ISC 和荧光速率的变化与最低单重态的性质有关，在激发分子的构型变化时，最低单重态从局域激发转变为电荷转移激发。这一发现为设计用于新兴发光材料应用的纯轻原子有机磷光分子开辟了一条替代策略。
