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

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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.