Minimum effort, maximum effect: modulating twisted intramolecular charge transfer for ultralong room temperature phosphorescence

Abstract

Achieving efficient organic ultralong room temperature phosphorescence (OURTP) hinges on populating and stabilizing triplet excitons. Herein, we demonstrate a “minimum effort, maximum effect” strategy by precisely modulating the twisted intramolecular charge-transfer (TICT) process in minimalist single-benzene luminophores (SBLs). A synergistic attenuation of steric hindrance in electron-donating groups and electron-withdrawing potency in accepting groups is shown to facilitate TICT formation. The resulting TICT state acts as a pivotal relay, efficiently narrowing the singlet–triplet energy gap (ΔE_ST) and enhancing spin–orbit coupling (SOC) to foster rapid intersystem crossing and triplet population. Subsequent stabilization of these triplet states is achieved through a rigid hydrogen-bonding network within a polyvinyl alcohol (PVA) matrix. This work establishes a direct correlation between TICT character and OURTP performance, revealing a molecular-level “butterfly effect”, where subtle structural modifications yield dramatic photophysical enhancements. The findings provide a novel paradigm for designing high-performance OURTP materials from simple and compact molecular systems.