INFLUENCE OF SUBSTITUTION ON THE ELECTRONIC-PROPERTIES OF BIANTHRONES

Bianthrones, which are based on two anthrone moieties connected by a double bond, are proposed as a molecular switch involving large conformational changes. Upon substitution, the electronic properties change significantly. Time-resolved optical measurements, such as picosecond excited state spectroscopy and nanosecond time-resolved fluorescence, investigate the excited state relaxation of both the substituted and unsubstituted molecule. Large differences are found in the transient spectra, recorded over the visible region, and their temporal behaviour. Comparison to similar measurements on anthracene identify local electronic states in the spectra. Additional electronic states are induced by substitution. The time decay shows a highly stabilized excited state in the substituted form. However, fine structure in the relaxation and the dependences of the fluorescence decay indicate complex decay mechanisms. These results are discussed in terms of the proposed conformational change.