Thermal quenching of fluorescence in condensed media

• Energy terms reducing fluorescent emission are identified by physical arguments.
• Mathematical methods to deal with non-radiative transitions are developed.
• Closed-form equations for the temperature dependent quantum yield are derived.
• A particularly well suited experimental study is chosen from the literature.
• Quantitative agreement of theoretical predictions with experimental results.

Environmental factors strongly affect the features of the electromagnetic spectra of fluorescent compounds hosted by material media. The shape of the absorption and emission peaks, their characteristic asymmetry and breadth, the Stokes shift and quantum yield are generally temperature dependent and heavily influenced by both the local and extended physical properties of the medium. The theoretical method used before to obtain the lineshape function is extended here to other terms of the interaction energy between the optically sensitive orbital and the hosting medium, which become significant when the spectral feature is broad. An analytical expression for the temperature dependent decay rate by non-radiative processes is obtained by this way. Comparison with experiment on thermal quenching gives agreement within the experimental uncertainty. The solvent polarity, its protic or aprotic character, hydrogen bonds, proximity effects and presence of quenchers are expected to enter through the coupling constants of the corresponding energy terms.