The host/guest type of excited-state proton transfer; A general review

Contemporary progress regarding guest/host types of excited-state double pr oton transfer has been reviewed, among which are the biprotonic transfer wi thin doubly H-bonded host/guest complexes, the transfer through a solvent b ridge relay, the intramolecular double proton transfer and solvation dynami cs coupled proton transfer. Of particular emphases are the photophysical an d photochemical properties of excited-state double proton transfer (ESDPT) in 7-azaindole and its corresponding analogues. From the chemical aspect, t wo types of ESDPT reaction, namely the catalytic and non-catalytic types of ESDPT, have been classified and reviewed separately. For the case of stati c host/guest hydrogen-bonded complexes both hydrogen-bonding strength and c onfiguration (i.e. geometry) play key roles in accounting for the reaction dynamics. In addition to the dynamical concern, excited-state thermodynamic s are of importance to fine-tune the proton transfer reaction in the non-ca talytic host/guest type of ESDPT. The mechanisms of protic solvent assisted ESDPT, depending on host molecules and proton-transfer models, have been r eviewed where the plausible resolution is deduced. Particular attention has been given to the excited-state proton transfer dynamics in pure water, ai ming at its future perspective in biological applications. Finally, the dif ferentiation in mechanism between solvent diffusive reorganization and solv ent relaxation to affect the host/guest ESPT dynamics is made and discussed in detail.