Intramolecular charge separation and transition state dynamics in anthracene/pyridinium supermolecules

The excited state dynamics of anthracene (donor) and pyridinium or pyridine (acceptor) composed supermolecules has been studied applying femtosecond transient absorption and picosecond time-resolved fluorescence techniques. From the analysis of spectral and temporal dynamics of sigma- and pi-bridged systems 1a-4a, the effects of molecular structure and environment on intramolecular charge separation in the excited state are differentiated. Two-step charge separation has been verified to occur for 2a and 3a in liquid environment by identifying neutral and radical ion states of the anthracene moiety on the sub picosecond time scale. Instead, after changing the substitution position of the acceptor to 3-pyridinium, charge separation does not occur. From evaluating the transient state dynamics in solvents of different polarity, rates for charge separation and relaxation can be quantified in terms of Marcus theory.