Excited-state proton transfer through water bridges and structure of hydrogen-bonded complexes in 1H-pyrrolo[3,2-h] quinoline: Adiabatic time-dependent density functional theory study

Proton transfer reaction is studied for 1H-pyrrolo[3,2-h]quinoline-water complexes [(PQ-([H.sub.2]O).sub.n], n=0-2) in the ground and the lowest excited singlet states at the density functional theory (DFT) level. The excited-state acid-base changes introduce a driving force for the proton transfer reaction, large relaxation and reorganization of the hydrogen bonded water bridge in [(PQ-([H.sub.2]O).sub.2] are required during the proton translocation from the pyrrole NH group to the quinoline nitrogen blocking the complete tautomerization in this type of solvate.