Fast photo-processes in triazole-based push–pull systems

Electron donor-acceptor compounds 1 (asymmetrical push-pull derivative) and 2 (symmetrical push-pull-push derivative) were studied in which one (push-pull) or two aniline units (push-pull-push) are connected to a biphenyl group via triazole linkers, made by "click" chemistry. Steady-state and time-resolved spectroscopies indicate that highly dipolar charge separated excited states are populated in moderately polar solvents. The very similar photophysical behavior of both compounds implies symmetry breaking in the excited state of 2. The polarity of the solvent determines the efficiency of formation of the charge separated state. While in toluene it is very low, it becomes very high in acetonitrile. The bis-triazole substituted biphenyl unit in 2 behaves as a better electron acceptor than the mono-triazole substituted biphenyl in 1, which leads to a more facile charge separation in 2. Rates of charge separation are of the order of 10(11)-10(12) s(-1), and increase with solvent polarity.