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Three Modes of Proton Transfer in One Chromophore: Photoinduced Tautomerization in 2‐(1 H ‐Pyrazol‐5‐yl)Pyridines, Their Dimers and Alcohol Complexes
Author(s) -
Vetokhina Volha,
Dobek Krzysztof,
Kijak Michał,
Kamińska Izabela I.,
Muller Keven,
Thiel Werner R.,
Waluk Jacek,
Herbich Jerzy
Publication year - 2012
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201200602
Subject(s) - tautomer , chromophore , chemistry , proton , photochemistry , alcohol , stereochemistry , organic chemistry , physics , quantum mechanics
Studies of 2‐(1 H ‐pyrazol‐5‐yl)pyridine (PPP) and its derivatives 2‐(4‐methyl‐1 H ‐pyrazol‐5‐yl)pyridine (MPP) and 2‐(3‐bromo‐1 H ‐pyrazol‐5‐yl)pyridine (BPP) by stationary and time‐resolved UV/Vis spectroscopic methods, and quantum chemical computations show that this class of compounds provides a rare example of molecules that exhibit three types of photoreactions: 1) excited‐state intramolecular proton transfer (ESIPT) in the syn form of MPP, 2) excited‐state intermolecular double‐proton transfer (ESDPT) in the dimers of PPP in nonpolar media, as well as 3) solvent‐assisted double‐proton transfer in hydrogen‐bonded 1:1 complexes of PPP and MPP with alcoholic partners. The excited‐state processes are manifested by the appearance of a dual luminescence and a bimodal irreversible kinetic coupling of the two fluorescence bands. Ground‐state syn–anti equilibria are detected and discussed. The fraction of the higher‐energy anti form varies for different derivatives and is strongly dependent on the solvent polarity and hydrogen‐bond donor or acceptor abilities.