Brian A. Pryor

Spectroscopy of jet-cooled polar complexes of aminophthalimides

Abstract The spectroscopy and excited-state lifetimes of 3- and 4-aminophthalimides (3AP, 4AP), N-methyl-4AP (NM4AP) and some complexes with polar molecules have been explored under supersonic jet conditions. Spectroscopic data, MM2-level structure calculations and rotational coherence spectroscopy show that a single water molecule attaches to 3AP by accepting a hydrogen bond from the imide > NH group. Whereas 3AP/H2O is present as a single species, the case of 4AP is complicated by the presence of two isomers, having significantly different fluorescence decay times and radiative lifetimes. This observation, which is repeated for methanol complexation, is evidence for the sensitivity of the electronic structure of 4AP to a site-specific interaction.

SPECTROSCOPY AND DYNAMICS OF JET-COOLED 2-METHOXYNAPHTHALENE

Abstract The S1−S0 electronic transition of jet-cooled 2-methoxynaphthalene has been investigated by the use of laser-induced fluorescence, dispersed fluorescence and time-resolved emission spectroscopy. Two electronic origin transitions were observed, separated by 660 cm−1. They are caused by the presence of a cis (syn) and a trans (anti) conformation of the methoxy group with respect to the naphthalene frame. Intramolecular vibrational energy redistribution was identified by vibrational quantum beats in the case of the cis isomer 978 cm−1 above the S1−S0 origin.

Perylene complexes with p-dichlorobenzene and related species: comparison of rotational coherence data with structure calculations

Abstract Rotational coherence experiments have been carried out on complexes of perylene with p-dichlorobenzene (DCB), p-difluorobenzene (DFB) and hexafluorobenzene, largely to seek an explanation for the unusually small complexation shifts of the first two. All three complexes were found to have overlapped, parallel ring structures, similar to that of perylene/benzene. Moreover, in structures corresponding to the electronic ground state, the halogen-halogen axes of DFB and DCB were found to be aligned perpendicular to the perylene long axis.

Rotational coherence spectroscopy of 9,9′-bifluorenyl: assignment of exciton components

Abstract Polarized time-resolved fluorescence measurements on the two 0 0 0 components of the exciton doublet of 9,9′-bifluorenyl yielded distinct sets of rotational coherence transients. These measurements allowed assignment of the transition moment vector for the lower-energy exciton component to ‘A’ symmetry within the point group C 2 . Hybrid transients observed for the other component confirmed ‘B’ symmetry. Also, we find the interannular twist angle between the two fluorene units to be 62±5°. Parallel behavior of the 1:1 complex of bifluorenyl with water suggests that the water molecule hydrogen-bonds symmetrically to both aromatic components.

Structural measurements of hydrogen-bonded complexes of perylene with water and methanol

Abstract Rotational coherence experiments have been carried out for 1:1 van der Waals complexes of perylene with water and methanol. The observed inertial properties are consistent with structures corresponding to potential-energy minima calculated via MM2 techniques. The results show that both types of complex involve hydrogen-bonding to π-electrons on the perimeter of the aromatic molecule.