Efficient monomolecular white emission of phenothiazine boronic ester derivatives with room temperature phosphorescence

Abstract

With the challenging aim to obtain efficient white emission from a single low-molar-mass organic emitter, four phenothiazine boronic ester derivatives (H-PTZ-Bpin, CHO-PTZ-Bpin, CN-PTZ-Bpin and PhCN-PTZ-Bpin) were synthesized by incorporating different electron withdrawing groups to the phenothiazine core. Efficient fluorescence with broadly varied emission colours from blue to orange and high photoluminescence quantum yields (PLQYs) reaching 67% were observed for the compounds in the solid-state. When one of the compounds was dispersed in the rigid polymeric host ZEONEX, the samples in vacuum demonstrated efficient white emission (PLQY of 33%) with the CIE1931 colour coordinates of (0.26, 0.31), colour rending index of 73, and colour temperature of 8145 K. The white emission resulted from blue fluorescence and yellowish room temperature phosphorescence (RTP) from the local excited singlet and triplet states. The RTP of the unsubstituted derivative was characterized by a relatively short lifetime of 23.91 ms and a high PLQY value of 17%. The white emission with a high PLQY of the compound was obtained due to the similar intersystem crossing rate of 1.6 × 10⁶ s⁻¹ and fluorescence relaxation rate of 1.6 × 10⁶ s⁻¹.