Faculty Publications

The Excited States and Vibronic Spectroscopy of Diphenyldiacetylene and Diphenylvinylacetylene

Document Type

Article

Journal/Book/Conference Title

Physical Chemistry Chemical Physics

Volume

14

Issue

1

First Page

173

Last Page

183

Abstract

Laser induced fluorescence (LIF) excitation scans and dispersed fluorescence (DFL) spectra have been recorded for two four-carbon α,ω-diphenyl systems, diphenyldiacetylene (DPDA, -CC-CC-) and trans-diphenylvinylacetylene (DPVA, -CHCH-CC-) as isolated molecules cooled in a supersonic expansion. While these molecules have similar conjugation length, they exhibit strikingly different vibronic spectroscopy and photophysics. The near-UV LIF excitation spectrum of diphenyldiacetylene has its electronic origin at 32158 cm-1, and a strong progression in the CC stretch (2156 cm-1). All transitions are inherently broad, with widths of ∼30 cm-1 fwhm or greater. The S1 origin DFL spectrum is composed of sharp transitions with Franck-Condon activity mirroring that in the excitation spectrum, and broad emission shifted well to the red ascribable to phosphorescence on the μs timescale. Using ab initio calculations, it is possible to show that DPDA exists as a single, planar conformer with D 2h symmetry. In contrast, trans-diphenylvinylacetylene shows intense sharp transitions in both LIF and DFL spectra with an S0-S 1 origin of 31183.2 cm-1 and long progressions involving the in-plane fundamentals ν53 (bridge-phenyl bending) and ν51 (bridge-phenyl stretch). A sharp reduction in fluorescence yield in DPVA occurs within 300 cm-1 of the S1 origin. Possible causes for the photophysical processes occurring in the two molecules are discussed.

Department

Department of Chemistry and Biochemistry

Original Publication Date

1-7-2012

DOI of published version

10.1039/c1cp22857a

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