Three Modes of Proton Transfer in One Chromophore: Photoinduced Tautomerization in 2‐(1H‐Pyrazol‐5‐yl)Pyridines,Their Dimers and Alcohol Complexes |
| |
| Authors: | Volha Vetokhina Dr Krzysztof Dobek Michał Kijak Izabela I Kamińska Keven Muller Prof Werner R Thiel Prof Jacek Waluk Prof Jerzy Herbich |
| |
| Institution: | 1. Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01‐224 Warsaw (Poland), Fax: (+48)?(22)?3433333;2. Faculty of Physics, Adam Mickiewicz University, Umultowska 85, 61‐614 Poznań (Poland);3. Faculty of Mathematics and Science, Cardinal Stefan Wyszyński University, Dewajtis 5, 01‐815 Warsaw (Poland);4. Kaiserslautern University of Technology, Erwin‐Schr?dinger‐Str. 52, 67653 Kaiserslautern (Germany) |
| |
| Abstract: | Studies of 2‐(1H‐pyrazol‐5‐yl)pyridine (PPP) and its derivatives 2‐(4‐methyl‐1H‐pyrazol‐5‐yl)pyridine (MPP) and 2‐(3‐bromo‐1H‐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. |
| |
| Keywords: | fluorescence hydrogen bonds kinetics photochemistry proton transfer |
|
|
