Freezing Out Vavilov's Rule: Temperature‐Dependent Fluorescence of a Rhodanine Dye

Racchi, Ottavia; Scurti, Stefano; Liotino, Stefano; Lanfranchi, Andrea; Painelli, Anna; Comoretto, Davide; Došlić, Nađa; Caretti, Daniele; Sissa, Cristina (2026) Freezing Out Vavilov's Rule: Temperature‐Dependent Fluorescence of a Rhodanine Dye. ChemPhotoChem, 10 (2). ISSN 2367-0932

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Official URL: http://doi.org/10.1002/cptc.202500255

Abstract

This study addresses the anomalous fluorescence of a rhodanine‐based organic dye of interest for nonlinear optical applications. At room temperature, the dye exhibits weak fluorescence, while spectra collected in glassy 2Me‐THF at 77 K show a surprising fluorescence intensity increase by several orders of magnitude with respect to room temperature. Moreover, a pronounced dependence of the fluorescence quantum yield on the excitation wavelength is observed, indicating a breakdown of Vavilov's rule, a corollary of Kasha's rule, which states that the fluorescence quantum yield is independent of the excitation energy. Quantum chemical calculations demonstrate the presence of a bright ππ* excited state that lies very close in energy to a dark nπ* state. The subtle interplay between these two excited states with different natures is responsible for the intriguing spectral behavior of the dye. Specifically, experimental results are rationalized in terms of a population branching between the two excited states, which can be tuned upon varying the temperature or the excitation energy.

Item Type:

Article

Uncontrolled Keywords:

rhodanine dye; anomalous fluorescence; excited-state dynamics

Subjects:

NATURAL SCIENCES > Chemistry

Divisions:

Division of Physical Chemistry

Projects: