Concentration-dependent nonradiative decay mechanisms in fluorescence self-quenching: insights from azulene and 1,3-dichloroazulene

A series of steady-state and time-resolved spectroscopies were performed on azulene (Az) and its 1,3-dihalogenated analogue, 1,3-dichloroazulene (DCAz). Understanding the intra/intermolecular interactions in these types of systems is the key to unlocking the potential of these molecules and enabling their application in a range of future devices. Therefore, the concentration dependence of their self-quenched fluorescence intensities and of the reduced lifetimes of their second-excited singlet states were examined. A Stern–Volmer analysis was implemented based on these experiments, which resulted in DCAz exhibiting a higher bimolecular quenching constant, compared to Az, due to its shorter excited-state lifetime. The highly efficient self-quenching at room temperature was a result of a short-range energy transfer mechanism.