Thermally Regulated Multistate Emission through Integrated Excited-State Engineering in Organic Luminophores

Abstract

Organic luminescent materials with multistate responsiveness to external stimuli are of growing interest for smart sensing, information encryption, and next-generation optoelectronic devices. However, achieving thermally tunable emission involving multiple excited-state mechanisms within a single molecule remains highly challenging. Here, we report a rationally designed donor–acceptor molecule, PTZT, that integrates aggregation-induced emission (AIE), thermally activated delayed fluorescence (TADF), and room-temperature phosphorescence (RTP) into one solid-state system. By combining a rigid electron-deficient triazine acceptor with a twisted donor and fine-tuned intramolecular charge transfer (ICT), PTZT exhibits both a small singlet–triplet energy gap (ΔE_S-T) and n−π* character, enabling a thermally driven interplay between fluorescence, delayed fluorescence, and phosphorescence. Remarkably, PTZT shows a nonmonotonic, three-stage temperature-dependent luminescence evolution, resulting from the dynamic switching of dominant excited-state pathways. Comprehensive photophysical studies and exciton kinetics modeling reveal the underlying mechanism of this triple-emission behavior. Furthermore, nondoped OLEDs based on PTZT demonstrate favorable electroluminescent performance, underscoring its potential for practical application. This work offers a new molecular strategy for constructing multiresponsive organic emitters with programmable thermal behaviors.