Investigation of the Emission Mechanism and Property Control of Highly Fluorescent Polyimides via Application of High Static Pressure

通过对聚酰亚胺（PI）薄膜施加高/超高压（1.0 ~ 90000 atm）静压力，研究了常规聚酰亚胺（PI）和高荧光PI的光吸收和荧光发射行为。在高压下，PI链之间的分子间距离有效减小，这直接增强了分子间电荷转移（CT）相互作用。此外，可以根据研究结果开发具有光学功能的新型热稳定pi。实验采用“高静液压力池法”和“金刚石砧（DA）法”分别对PI薄膜施加高压（< 400mpa）和甚高压（< 10gpa）。利用常规光谱学和显微分光光度法对高压下生成的PI薄膜的光学性质和结构变化进行了精确测量。此外，这些实验还部分阐明了高荧光pi在高量子产率（0.3或更高）下荧光发射的光物理机制。此外，还观察到各种有趣的现象，这些现象有助于开发具有高功能的新型热稳定光学材料。此外，本研究开发的方法和实验结果有利于提高高荧光pi的性能，提高量子产率和强白光的发射。

The investigators aimed to clarify the photo-absorption and fluorescent emission behaviors of conventional polyimides (PIs) and highly fluorescent PIs by applying high/very high static pressure (1.0-90,000 atm) to PI thin films. The intermolecular distances between PI chains are effectively reduced at elevated pressures, which straightforwardly enhance the intermolecular charge transfer (CT) interactions. In addition, novel thermally stable PIs having optical functionalities can be developed based on findings. For the experiments, "high hydrostatic pressure cell method" and "diamond anvil (DA) method" were adopted to apply high (<400 MPa) and very high pressures (<10 GPa) to PI thin films, respectively. The variations in optical properties and structural changes of the PI films generated at high pressures were precisely measured by using not only conventional spectroscopies but also micro spectrophotometric techniques. Furthermore, the photophysical mechanisms of the fluorescent emission at high quantum yields (0.3 or more) observed for the highly fluorescent PIs were partly clarified by these experiments. In addition, various interesting phenomena which lead to the development of novel thermally stable optical materials having high functionalities were observed. Moreover, the methods developed in this study and the findings obtained in the experiments are beneficial to improve the performance of the highly fluorescent PIs with increasing the quantum yields and the emission of strong white luminescence.