Conformation-determined emission enhancement of phenothiazine derivatives under high pressure†

For organic luminescent materials, molecular conformation is a basic parameter, which significantly influences their photophysical properties and has been a subject of investigation. In this work, we found that the phenothiazine derivative of PTZ-DP-F crystal presented a continuous emission enhancement until the pressure was up to 2.31 GPa. Unlike the crystal state, the short wavelength emission derived from the quasi-axial conformation of the ground powder state was still enhanced at a relatively lower pressure range, revealing that the pressure-induced emission enhancement (PIEE) behaviors are highly related to the conformation discrepancy. Then, combined with the theoretical calculation results, it further confirmed that the enhanced emission at the initial stage should be ascribed to the restriction of intramolecular rotation and vibrations as a result of the enhanced intra-/inter-molecular interactions under high pressure. Additionally, the other phenothiazine derivatives were also chosen for high-pressure experiments to further prove the conformation-dependent pressure-responsive behaviors. Our study provides deep insights into the essential role of intra-/inter-molecular interactions in photo-physical properties to develop a mechanism of PIEE determined by molecular conformation for phenothiazine derivatives and successfully forging new paths for the designing of materials with high luminous efficiency by regulating the intramolecular interactions.