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Solvent‐Dependent Photoacidity State of Pyranine Monitored by Transient Mid‐Infrared Spectroscopy
Author(s) -
Mohammed Omar F.,
Dreyer Jens,
Magnes BenZion,
Pines Ehud,
Nibbering Erik T. J.
Publication year - 2005
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.200400510
Subject(s) - pyranine , chemistry , solvation , excited state , deuterium , spectroscopy , photochemistry , picosecond , raman spectroscopy , infrared spectroscopy , ultrafast laser spectroscopy , chemical physics , solvent , atomic physics , laser , organic chemistry , optics , biochemistry , physics , quantum mechanics , membrane
We investigate with femtosecond mid‐infrared spectroscopy the vibrational‐mode characteristics of the electronic states involved in the excited‐state dynamics of pyranine (HPTS) that ultimately lead to efficient proton (deuteron) transfer in H 2 O (D 2 O). We also study the methoxy derivative of pyranine (MPTS), which is similar in electronic structure but does not have the photoacidity property. We compare the observed vibrational band patterns of MPTS and HPTS after electronic excitation in the solvents: deuterated dimethylsulfoxide, deuterated methanol and H 2 O/D 2 O, from which we conclude that for MPTS and HPTS photoacids the first excited singlet state appears to have charge‐transfer (CT) properties in water within our time resolution (150 fs), whereas in aprotic dimethylsulfoxide the photoacid appears to be in a nonpolar electronic excited state, and in methanol (less polar and less acidic than water) the behaviour is intermediate between these two extremes. For the fingerprint vibrations we do not observe dynamics on a time scale of a few picoseconds, and with our results obtained on the OH stretching vibration we argue that the dynamic behaviour observed in previous UV/Vis pump–probe studies is likely to be related to solvation dynamics.