Abstract
Bridging the gap between the photophysical properties of organic molecules in solution and their performance in bulk materials and devices remains a major challenge in many areas, including organic electronics. The pathway from fundamental studies of intermolecular interactions in the liquid phase to the development of solid-state sensor materials has been traced using boron difluoride β-diketonate , derivatives. The ability of boron difluoride β-diketonates to form exciplexes with arenes makes them promising molecular probes. The materials can be obtained, for example, by covalently attaching fluorophores to the surface of silica nanoparticles. The primary focus in this study is placed on establishing the key mechanisms responsible for the non-radiative deactivation of excited states of the investigated class of molecules in solution. It was demonstrated that the dominant process involves changes in the molecular geometry upon excitation. This understanding allows for the design of non-fluorescent molecules where the non-radiative process dominates over the radiative one . The influence of electron-donating and electron-withdrawing substituents in a series of fluorophore derivatives on the efficiency of exciplex formation with arenes was investigated. Exciplex formation successfully competes with non-radiative deactivation. This provides a basis for the development of molecular probes that selectively activate ("turn on") luminescence upon interaction with aromatic compounds . It is shown that the efficiency of such probe systems can be enhanced by transitioning to multichromophoric architectures. The transformation of the photophysical mechanisms identified in solution upon transfer to solid-state materials with covalently immobilized fluorophores was analysed. The obtained results reveal how molecular photophysical processes are modified upon immobilization on a solid-state surface and provide guidelines for the design of sensor materials with a controlled luminescence response.