Journal of Physical Chemistry p. 7927 - 7935 (1990)
Update date:2022-08-17
Topics:
Morgan, Meredith A.
Orton, Edward
Pimentel, George C.
Intramolecularly hydrogen bonded o-hydroxybenzaldehyde (OHBA-C) isolated in 12 K rare gas matrices photolyzes to a non-hydrogen-bonded rotamer (OHBA-F).IR spectra of OHBA-C, OHBA-F, and several model and isotopically substitued compounds are consistent with identification of the OHBA-F conformer as that formed by 180-deg rotation of both the hydroxy and aldehyde groups.For the two rotamers, electronic absorption, excitation, and emmission spectra are presented together with time-resolved emission measurements and estimates of a ground-state reaction enthalpy.From these data, it is proposed that the S1 state of OHBA-C is an n,?* hydrogen atom transfer-state, and S2 is a ?,?* proton-transfer state with a large ( ca. 18 kcal) barrier to reaction.Rotamerization is reversed by S1 or S2 excitation of OHBA-F.The conversion of OHBA-C to OHBA-F is ca. 5 times as efficient as the reverse process upon excitation at the respective S1 0-0 energies.An increase in photolysis quantum yield of OHBA-C is measured at energies well above the 0-0 energy and may correspond to reaction over the proposed ca. 8 kcal S1 barrier.
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