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 the excited state. Theoretical calculations reveal complete spatial separation of electrons and holes in the D₁ state of TSCT-TR, contrasting with localized or through-bond charge transfer (TBCT) characteristics observed in control radicals. Femtosecond transient absorption spectroscopy confirms significantly prolonged excited-state lifetimes of TSCT-TR – up to ∼80 ps in polar solvents. Moreover, the developed synthetic intermediates allow for modular derivatization of triazolyl radical systems. This work demonstrates TSCT in stable radicals, offering a versatile platform for designing long-lived charge-separated states in organic radical-based optoelectronic and photonic applications.