Anti-Kasha Emission in Organic Radicals: Mechanistic Insights and Experimental Caveats

Abstract

Organic radicals have recently emerged as promising candidates for luminescent materials, often exhibiting emissions that challenge the traditional Kasha's rule. While a growing number of reports claim anti-Kasha emission from higher excited states in radicals, the photophysical origins of such emissions remain ambiguous. In this Concept, we critically assess the mechanistic underpinnings of anti-Kasha behavior in radical systems and highlight the experimental caveats that may lead to misinterpretation—including emission from closed-shell impurities, photodegradation byproducts, or incomplete radical formation. By revisiting key examples and providing a framework for rigorous spectral validation, this article aims to recalibrate the standards of evidence in radical photophysics and guide the development of reliable design strategies for high-energy emitters.