Picosecond observation of cation-stepwise delayed and cation-triggered photoinduced intramolecular charge transfer in fluorescent cation probes
Résumé
Time-resolved transient absorption and gain spectra with subpicosecond laser excitation are reported for donor-donor and acceptor-donor stilbene-crowns (in each compound the electron donor group is the 15-aza-5-crown macrocycle, D1). The effect of the calcium cation on the photoinduced intramolecular charge transfer (ICT) rate constants are measured. When the cation is on the donor side of the molecular system (class 1: D1CS-Crown), the photoinduced ICT process is slowed down and goes through several intermediates characterized by a distancing of the cation, while a solvent molecule enters its coordination sphere. When the cation is on the acceptor side (class 2: D1DS-Crown,D1DB-Crown and D1DCS-Crown), the photoinduced ICT process becomes too fast to be measured, even on the picosecond scale.