Through-Space Charge Transfer in a Stable 1,2,4-Triazolyl Radical Enabled by Spiro D–σ–A Architecture for Prolonged Excited-State Lifetimes

Abstract

Stable organic radicals are promising building blocks for next-generation optoelectronic materials, yet their excited-state charge dynamics remain largely unexplored. Herein, we report a novel 1,2,4-triazolyl radical (TSCT-TR) incorporating a rigid spiro-based donor–σ–acceptor (D–σ–A) framework that exhibits distinct through-space charge transfer (TSCT) behavior in excited state. Theoretical calculations reveal complete spatial separation of electron and hole in the D₁ state of TSCT-TR, contrasting with localized or through-bond charge transfer (TBCT) characters observed in control radicals. Femtosecond transient absorption spectroscopy confirms significantly prolonged excited-state lifetimes of TSCT-TR—up to ~80 ps in polar solvent. Moreover, the developed synthetic intermediates allow for modular derivatization of triazolyl radical systems. This work represents the demonstration of TSCT in stable radical, offering a versatile platform for designing long-lived charge-separated states in organic radical-based optoelectronics and photonic applications.