Theoretical and experimental studies of molecular photodegradation in π-conjugated chromophores with resonant and nonresonant excitation relative to the lowest-energy electronic transition of the chromophore are performed. The limitations of previous photodegradation models are discussed, and new models that overcome these limitations and provide more accurate estimates of chromophore photostability are presented. In particular, the necessity of considering multiple degradation pathways in the analysis of photobleaching studies is shown. Photostability studies of a dihydrofuran thiophene-bridged dicyanomethylene based chromophore (FTC) employing excitation reveal that the photoinitiated decay kinetics are biphasic. We present what we believe to be a new, double-pathway photodegradation model capable of describing this behavior. Through investigations employing the singlet-oxygen quencher bis(dithiobenzil)nickel, photooxidation is shown to be one of the photodegradation pathways, and the ability of a quencher to inhibit chromophore photooxidation is quantified. The studies presented here provide insight into the mechanism of photochemical degradation of π-conjugated chromophores for devices operating in the visible and at telecommunication wavelengths.
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