基于双磷光和分子平面性修饰的单分子长余辉白光的设计

White afterglow emissive molecules are of great significance in areas such as no-background night illumination display and biomedical diagnosis. The most common single white emissive molecules are those with dual fluorescence or fluorescence/phosphorescence emission. Molecules with dual fluorescence emission cannot be used to achieve long afterglow emission. Molecules with fluorescence/phosphorescence emission have white light distortion due to large difference in lifetime. Designing white emissive molecules with dual phosphorescence emission can effectively avoid white light color distortion. However, due to Kasha's rule, phosphorescence is mostly derived from the lowest triplet state (T1). This project intends to design a single-molecule white light based on dual phosphorescence by inducing phosphorescence from a higher triplet state (Tn(n≥2)) through molecular modification and environmental regulation of the molecule. The contents are as follows: (1) The white light is obtained by the combination of blue-green light and orange-yellow light: the purely organic phosphorescent molecule with longer conjugation length is studied based on common phosphorescent molecular structure (mostly green light) to let the phosphorescence of T1 be orange-yellow light; the molecular structure characteristics and physical properties of the environment of molecules with phosphorescence from second triplet state are studied, and the phosphorescence derived from Tn(n≥2) is modified to be blue-green light. White light will be obtained based on dual phosphorescence emission. (2) Designing afterglow white light molecules based on molecular structure planarity modification and utilizing side groups with low heavy atom effect; (3) Improving the luminescence efficiency of purely organic phosphorescent materials on amorphous polymer matrix. Finally, a purely organic white emissive molecule with afterglow emission on amorphous state is realized based on dual phosphorescence, which can provide materials and devices fabricating theories as well as methods.

长余辉白光在无背景照明显示及医学诊断等领域意义重大。常见的白光分子多为具有双荧光或荧光/磷光的分子，双荧光无法实现长余辉，荧光/磷光寿命差别较大会出现白光色彩失真。设计具有双磷光的白光分子可有效避免白光失真，但由于Kasha规则，磷光多源于最低三重态（T1）。本项目拟通过分子修饰和其所处环境调节诱导源于较高三重态(Tn(n≥2))的磷光，进而设计基于双磷光的单分子白光。主要研究：(1)利用蓝绿光和橙黄光组合获得白光：在常见磷光分子结构（多为绿光）基础上设计具有更长共轭的磷光分子，使其来源于T1的磷光为橙黄光；研究产生第二三重态磷光分子的结构特点及所处环境特性，诱导Tn(n≥2)磷光，调节使其为蓝绿光；(2)基于分子平面性修饰并利用重原子效应较低的侧链基团，获得长余辉白光；(3)提高非定形纯有机磷光的发光效率。最终实现非定形长余辉白光，为无背景照明显示提供材料和器件制备理论及方法。

本项目提出了基于纯有机双三重态磷光发射实现长余辉白光的设计思想，发现羰基能够诱导三重态的布居；卤素的重原子效应可增强磷光。非极性分子作为固体支撑可增加分子环境的刚性和对三重态的保护，有效延长磷光寿命。发现从室温逐渐降低温度时，所研究卤素苯甲醛体系磷光波长红移了20 nm，发现在低温下发光为单寿命衰减，而室温下为双寿命衰减规律，高能级到基态的跃迁速率更快，因此具有较短的寿命，因此常温下两个成分的发光分别为低能级(T1)和高能级(T2)的磷光发射。基于延迟磷光的检测，发现时间延迟后发光也出现红移，表明低能级具有较长的寿命。发现处于极性大的环境下的分子在短波长会出现双寿命曲线规律。发现随着环境极性增加，降温引起的红移更加明显。发现室温下处于非极性环境下的分子已经红移，且寿命曲线为长寿命的单一衰变曲线，说明室温下处于非极性环境下的分子只发射低能级的磷光，且为长寿命部分；而处于极性环境下的分子寿命曲线为双寿命衰减规律，且以短波长高能级的发光为主。发现随着极性增加，磷光红移，说明极性环境能够降低三重态能级，使得发光出现红移。发现用Cl取代时，寿命最长，在氯、溴、碘三种元素中，氯元素的重原子效应最小，因此，得到了最长的寿命。在本项目的资助下，共发表SCI论文7篇，均对本项目进行了标注，其中二区论文6篇，三区论文1篇。授权国家发明专利1项。指导学生参加各类学科竞赛并获得国家级奖励。长余辉白光材料对于无背景照明、显示及生物医学诊断意义重大。从纯有机磷光材料中获得长余辉白光是有效的途径。本项目从单一有机材料获得了双磷光发射，为基于双磷光实现白光提供了思路，目前课题正在进行侧链修饰，改变双发射的波长，有望在不久将来获得双磷光长余辉白光。