title: Separation of different hydrogen-bonded clusters by femtosecond UV-ionization-detected infrared spectroscopy: 1H-pyrrolo[3,2-h]quinoline.(H2O)(n=1,2) complexes.
abstract: Experimental and theoretical studies are presented for complexes of water with 1H-pyrrolo[3,2-h]quinoline (PQ), a bifunctional compound acting simultaneously as a hydrogen-bond donor and acceptor. A 1:1 complex, which is not fluorescent and only very short-lived in the electronically excited state, was analyzed by isolating the complex under supersonic jet conditions and characterizing its structure by infrared-induced ion depletion spectroscopy utilizing multiphoton ionization by femtosecond UV pulses (IR/fsMPI spectroscopy). On the other hand, a long-lived 1:2 complex was identified as the smallest microhydrate of PQ contributing to the laser-induced fluorescence excitation spectrum. Its structure was assigned by fluorescence-detected IR spectra and analyzed using density functional theory. The structures of the 1:1 and 1:2 clusters are assigned to species in which the water molecule(s) form a hydrogen-bonded solvent bridge between the two functional groups. In accord with calculations, both 1:1 and 1:2 PQ/water complexes reveal weaker hydrogen bonding than the analogous clusters of PQ with methanol.
authors.affiliation: Institute of Physical and Theoretical Chemistry, University of Frankfurt, Max-von-Laue-Str. 7, 60438 Frankfurt/M, Germany.
authors.forename: Yevgeniy
authors.initials: Y
authors.lastname: Nosenko
authors.forename: Maksim
authors.initials: M
authors.lastname: Kunitski
authors.forename: Christoph
authors.initials: C
authors.lastname: Riehn
authors.forename: Randolph P
authors.initials: RP
authors.lastname: Thummel
authors.forename: Alexander
authors.initials: A
authors.lastname: Kyrychenko
authors.forename: Jerzy
authors.initials: J
authors.lastname: Herbich
authors.forename: Jacek
authors.initials: J
authors.lastname: Waluk
authors.forename: Bernhard
authors.initials: B
authors.lastname: Brutschy