Multi-resonance emitters with room-temperature phosphorescence in amorphous state and excited by visible light

Abstract

Unlike boron, nitrogen-containing multi-resonance emitters with thermally activated delayed fluorescence, here we report boron, sulfur (B, S)-based multi-resonance emitters with room-temperature phosphorescence (RTP) by inserting thiophene into a 5,9-dithia-13b-boranaphtho[3,2,1-de]anthracene skeleton that simultaneously realizes large singlet–triplet energy splitting and strong spin–orbital coupling, leading to efficient room-temperature phosphorescence in an amorphous state. Unlike most RTP emitters with ultraviolet excitation, the multi-resonance RTP emitters exhibit strong phosphorescence under daily-use blue/white LED lamps owing to their intense absorption in the visible-light region (400–486 nm). Meanwhile, such RTP behavior can be tuned by the number and fusing pattern of the thiophene moieties, with the emitters containing thiophene linked to boron atoms via α-positions exhibiting bathochromatically shifted emissions and longer phosphorescence lifetimes (47.7–119.4 ms) than those with β-position linkages. Given these features, amorphous RTP films with different emission colors and lifetimes are fabricated by dispersing the emitters in a poly(methyl methacrylate) matrix, and their applications in multi-color anti-counterfeiting are presented. These findings thus open a way to develop multi-resonance emitters as a new family of pure organic RTP materials that can work in an amorphous state and under visible-light excitation.