Annulative π-extension of phenothiazines: access to room temperature ultralong organic phosphorescent materials

Here is reported the first example of annulative π-extension of phenothiazines to develop ultralong-lifetime room-temperature phosphorescent (RTP) materials based on a stepwise adjustment strategy. Through systematic modification of substituents and the degree of conjugation, the energy levels and spin-orbit coupling (SOC) values of the preliminary phosphorescent skeleton were systematically optimized, leading to the development of ultralong-lifetime RTP materials. In this work, we have developed the phenothiazine-class material with the longest-recorded phosphorescence lifetime (over 1.5 seconds) and a 15-second afterglow. Moreover, for the first time, ultralong-lifetime red RTP materials within the phenothiazine family are reported, featuring emission peaks at 644 nm and 660 nm and lifetimes of 273 milliseconds and 230 milliseconds. The novel RTP materials have demonstrated excellent applications in anti-counterfeiting, multilevel encryption, white light-emitting diodes (LEDs), optical security, luminescent display technologies, dual-channel cellular imaging, and photocatalysts. Meanwhile, the design and synthesis strategy via π-extension of phenothiazine derivatives represents a highly promising pathway for developing ultralong-lifetime RTP materials.