Spin-Correlated Wavelength-Intensity Dual Modulation in Organic Diradicals via Excited-State Channel Engineering.

Abstract

Luminescent diradicals translate open-shell spin dynamics into optical readouts, yet their spin-dependent responses have largely been confined to emission-intensity changes, while concurrent wavelength modulation remains rare. Here, we introduce a through-space charge-transfer (TSCT) strategy in which appending a δ-carboline donor to a carbazole-bridged diradical preserves the native through-bond charge-transfer (TBCT) pathway while introducing a higher-energy TSCT-related emissive channel. At low temperature, δCbCz(TTM)2 exhibits pronounced magnetoluminescence (MagLum) enhancement together with an approximately 31 nm field-induced blue shift, while zero-field warming from 4.5 to 20 K produces an approximately 25 nm blue shift. Temperature-dependent MagLum measurements show that the additional spectral and intensity changes induced by the magnetic field are rapidly attenuated upon warming, supporting a common spin-dependent mechanism. The structural analogue αCbCz(TTM)2 exhibits a similar dual response with a smaller wavelength shift, highlighting the sensitivity of the response to donor topology. Time-resolved spectroscopy, variable-temperature EPR, and quantum-chemical calculations support a spin-correlated photophysical model in which magnetic and thermal perturbations regulate spin-dependent population redistribution, thereby modulating the relative contributions of TBCT- and TSCT-related emissive channels and producing correlated changes in emission intensity and wavelength. This work establishes through-space excited-state channel engineering as a route for extending spin-correlated luminescence beyond intensity-only modulation.

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