Pathways of S1 decay in phenol, indoles, and water complexes of phenol and indole in a free jet expansion

Abstract

Pumpprobe photoionization in a supersonic free jet has been used to determine quantum yields and rates of intersystem crossing from the SI state of phenol, phenol-H20, indole, indole-H20, and a variety of substituted indoles. Refined data analysis plus a more complete accounting of photofragmentation has resulted in lower intersystem-crossing quantum yields in phenol and phenol-H20 than previously reported. Intersystem-crossing quantum yields of all the indole compounds studied were found to be similar except for 2,3-dimethylindole for which evidence is presented for the existence of predissociation of the 'Lb origin level.The role of phenyl torsion in the excited-state dynamics of 3-hydroxyflavone (3HF) has been studied by use of time-resolved and static emission spectroscopies. 3HF, 2'-Me-3HF, 4'-Me3HF, and 3-hydroxychromone were studied in aprotic solvents and in 10 K argon matrices. The results show that in all cases excited-state proton transfer occurs very rapidly (<lo ps). This is followed by a -15-ps concerted vibrational relaxation/phenyl torsion process in hydrocarbon solutions. In the 10 K argon matrix environment, phenyl torsion is restricted and vibrational relaxation takes place on the 100-ps time scale.

Zero kinetic energy spectroscopy of hydroquinone-water (1:1) complex: A probe for conformer assignment

“…The magnitude of increase in the binding energy in the cationic state relative the neutral ground state is comparable with that reported for the phenol-water. 16,19 The ionization energies were also computed at various levels of theory as the difference between the optimized energies of the ground state ͑S 0 ͒ and cationic state ͑D 0 ͒. The zero point energy correction ͑⌬ZPE͒ was also included to obtain more accurate result.…”

“…The field-free ionization potential can be obtained by extrapolation to zero field by determining the field shift ͑␦͒ according to the formula ␦ ͑cm −1 ͒ = cE 1/2 , where c is a constant and E is the field strength in V/cm. 15,16 For molecular clusters such as phenol-water, the value of c is normally taken as 4.5 ͑Ref. 17͒ for all practical purposes.…”

Has the Excited State Proton Transfer Ever Been Observed in Phenol−(NH3)n Molecular Clusters?

“…The PhOH-(NH 3 ) 6 cluster seems to be an intermediate case: 6 ions are observed only weakly, indicating that the H transfer is less efficient, and one photon ionization thresholds indicate that ground-state proton transfer has occurred. It could be that, for the 1-6 cluster, the two ground-state structures, neutral and ion pair, are isoenergetic.…”

“…[1][2][3] The recent paper of the group of M. Fujii, probing the NH 4 (NH 3 ) n-1 radical product coming from the reaction, has definitively assessed that, for small clusters, the PhOH*-(NH 3 ) n excited-state dynamics are governed by the H transfer mechanism. 4 In the 1-1 complex, the reaction is indirectly evidenced by measurement of the excited PhOH*-(NH 3 ) complex lifetime, which is abnormally short (1 ns or less as compared to lifetimes of the order of 10 ns for other phenol-solvent complexes [5][6][7][8][9] ). This lifetime has been shown to be strongly dependent on the intermolecular vibration σ, the excitation of this mode leading to a strong decrease of the lifetime.…”

High resolution UV spectroscopy of phenol and the hydrogen bonded phenol-water cluster

“…They were found to vary considerably with cluster size. [32][33][34][35] A study of the sensitized phosphorescence spectra of phenol͑H 2 O͒ n clusters was performed by Goto et al 36 Significant phosphorescence was found when the nϭ3 and nϭ4 cluster origins were excited. The phenol͑H 2 O͒ 1 cation radical was investigated by Dopfer et al [37][38][39] experimentally using zero-kinetic-energy photo-electron spectroscopy ͑ZEKE͒, and theoretically via an ab initio study by Hobza et al 40 They used the 0 0 0 , the stretching and the in-plane wagging vibration as intermediate S 1 levels for obtaining ZEKE spectra and found an increase in vibrational frequencies in the cation compared to the S 1 state.…”