Deuteration effects on the vibronic structure of the fluorescence spectra and the internal conversion rates of triangular [4]phenylene

C. Dosche; M. U. Kumke; H.-G. Löhmannsröben; F. Ariese; A. N. Bader; C. Gooijer; O. Š. Miljanić; M. Iwamoto; K. P. C. Vollhardt; R. Puchta; N. J. R. van Eikema Hommes

doi:10.1039/B414545C

Deuteration effects on the vibronic structure of the fluorescence spectra and the internal conversion rates of triangular [4]phenylene

C. Dosche,^a M. U. Kumke,^a H.-G. Löhmannsröben,*^a F. Ariese,^b A. N. Bader,^b C. Gooijer,^b O. Š. Miljanić,^c M. Iwamoto,^c K. P. C. Vollhardt,^c R. Puchta^d and N. J. R. van Eikema Hommes^d

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^a Institute of Chemistry, University of Potsdam, Karl-Liebknecht-Str. 24-25, Germany
E-mail: loeh@chem.uni-potsdam.de
Fax: +49-331 977 5058
Tel: +49 331 977 5222

^b Department of Analytical Chemistry and Applied Spectroscopy, Vrije Universiteit, De Boelelaan 1083, The Netherlands

^c Center for New Directions in Organic Synthesis, Department of Chemistry, University of California at Berkeley and the Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, USA

^d Computer-Chemie-Centrum, Universität Erlangen-Nürnberg, Nägelsbachstr. 25, Germany

Abstract

Deuteration effects on the vibronic structure of the emission and excitation spectra of triangular [4]phenylene (D_3h [4]phenylene) were studied using laser-excited Shpol’skii spectroscopy (LESS) in an octane matrix at 4.2 K. For correct assignment of the vibrational modes, the experimental results were compared with calculated frequencies (B3LYP/6-31G*). CH vibrations were identified by their characteristic isotopic shifts in the spectra of deuterated triangular [4]phenylenes. Two CC stretching modes, at 100 cm⁻¹ and 1176 cm⁻¹, suitable as probes for bond strength changes in the excited state, were identified. The isotope effect on the internal conversion rates of triangular [4]phenylene was evaluated from measurements of temperature dependent lifetime. Isotope dependency and the magnitude of the internal conversion rates indicate that internal conversion in triangular [4]phenylene is most likely induced by CH vibrations. The results obtained by LESS and lifetime measurements were compared with PM3 PECI calculations of the excited state structure. The theoretical results and the relation between ground and excited state vibration energies of the 1176 cm⁻¹ probe vibration indicate a reduction of bond alternation of the central cyclohexatriene ring in the excited state.

Physical Chemistry Chemical Physics

Deuteration effects on the vibronic structure of the fluorescence spectra and the internal conversion rates of triangular [4]phenylene

Abstract

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Deuteration effects on the vibronic structure of the fluorescence spectra and the internal conversion rates of triangular [4]phenylene

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