Crosslink-Enhanced Emission-Dominated Design Strategy for Constructing Self-Protective Carbonized Polymer Dots With Near-Infrared Room-Temperature Phosphorescence.

Self-protective carbonized polymer dots (CPDs) with advantageous crosslinked nano-structures have attracted considerable attention in metal-free room temperature phosphorescence (RTP) materials, whereas their RTP emissions are still limited to short wavelength. Expanding their RTP emissions to Near-Infrared (NIR) range is attractive but suffers from the difficulties in constructing narrow energy levels and inhibiting intense non-radiative decay. Herein, a crosslink-enhanced emission (CEE)-dominated construction strategy was proposed, achieving desired NIR RTP (710 nm) in self-protective CPDs for the first time. Structural factors, i.e., crosslinking (covalent-bond CEE), conjugation (conjugated amine with bridging N-H and C=C group), and steric hindrance (confined-domain CEE), were confirmed indispensable for triggering NIR RTP emission in CPDs. Contrast experiments and theoretical calculations further revealed the rationality of the design strategy originating from CEE in terms of promoting the narrow energy level emission of triplet excitons and inhibiting the non-radiative quenching. This work not only firstly achieves NIR RTP in self-protective CPDs but also helps understand the origin of NIR RTP to further guide the synthesis of diverse CPDs with efficient long-wavelength RTP emission.