title: Fluorescence quenching in cyclic hydrogen-bonded complexes of 1H-pyrrolo[3,2-h]quinoline with methanol: cluster size effect.
abstract: Laser induced fluorescence (LIF) excitation spectra of molecular complexes of 1H-pyrrolo[3,2-h]quinoline (PQ) with methanol (n= 1, 2, 3) as well as vibrational spectra of their electronic ground state are reported. The latter have been recorded in the mid-infrared region by fluorescence depletion (FDIR). The only PQ.methanol(n) complex clearly identified in the LIF spectrum is the triply hydrogen-bonded cyclic 1 ratio 2 aggregate. Its stoichiometry has been proven by the femtosecond multiphoton ionization detected infrared measurements [J. Am. Chem. Soc., 2006, 128, 10 000]. The structure of the 1 ratio 2 cluster is determined by means of FDIR spectroscopy in combination with ab initio and DFT calculations. No fluorescence was detected that could be attributed to the 1 ratio 1 cluster. This behaviour of the 1 ratio 1 complex is explained in terms of rapid excited state double proton transfer followed by a non-radiative relaxation. The n= 3 and heavier clusters are fluorescent. Their electronic spectra overlap, preventing the selective measurement of the FDIR spectra of individual complexes.
authors.affiliation: Institut für Physikalische und Theoretische Chemie, J. W. Goethe-Universität, Max-von-Laue-str. 7, 60438, Frankfurt am Main, Germany.
authors.forename: Yevgeniy
authors.initials: Y
authors.lastname: Nosenko
authors.forename: Alexander
authors.initials: A
authors.lastname: Kyrychenko
authors.forename: Randolph P
authors.initials: RP
authors.lastname: Thummel
authors.forename: Jacek
authors.initials: J
authors.lastname: Waluk
authors.forename: Bernhard
authors.initials: B
authors.lastname: Brutschy
authors.forename: Jerzy
authors.initials: J
authors.lastname: Herbich
mesh_terms: D000465:Algorithms; D004583:Electrons; D005453:Fluorescence; D006859:Hydrogen / Q000737:chemistry*; D006860:Hydrogen Bonding; D007834:Lasers; D000432:Methanol / Q000737:chemistry*; D008958:Models, Molecular; D011522:Protons; D011758:Pyrroles / Q000737:chemistry*; D011804:Quinolines / Q000737:chemistry*; D013050:Spectrometry, Fluorescence / Q000379:methods; D019265:Spectroscopy, Near-Infrared / Q000379:methods
chemical_list: D011522:Protons; D011758:Pyrroles; D011804:Quinolines; D006859:Hydrogen; D000432:Methanol