Conformational Dynamics of Semiflexibly Bridged Donor−Acceptor Systems Studied with a Streak Camera and Spectrotemporal Parametrization of Fluorescence

The fluorescence of four semiflexibly bridged donor−bridge−acceptor systems was studied with a streak camera system. The information-rich streak data make a detailed analysis possible of both the kinetics and the spectral changes that take place. From the analysis, it follows that all compounds studied undergo a photoinduced harpooning process in which long-range electron transfer creates an extended charge-transfer (ECT) species, which converts to a compact charge-transfer (CCT) species due to Coulombic attraction. Both the ECT and CCT species display CT fluorescence. The harpooning process occurs even in solvents of medium polarity (e.g., diethyl ether), whereas it has previously been assumed for related compounds that this process only occurs in the gas phase and in nonpolar alkane solvents.