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Communication

Experimental Evidence for the Photoisomerization of Higher Fullerenes

Clemens Burda,*^† Anna C. S. Samia,^† David J. Hathcock,^‡ Houjin Huang,^§ and Shihe Yang*^§

Department of Chemistry, Case Western Reserve University, Cleveland, Ohio 44106, Laser Dynamics Laboratory, Department of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332, and Department of Chemistry, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong

J. Am. Chem. Soc., 2002, 124 (42), pp 12400–12401

DOI: 10.1021/ja027272h

Publication Date (Web): October 1, 2002

To whom correspondence should be addressed. E-mail: burda@po.cwru.edu.

†

Case Western Reserve University.

‡

Georgia Institute of Technology.

Hong Kong University of Science and Technology.

Abstract

The initial relaxation dynamics of the photoexcited fullerenes C₆₀, C₇₀, C₇₆, C₈₄, C₈₆, and C₉₀ were investigated by dispersion-free femtosecond pump−probe spectroscopy. Under identical excitation conditions, the formation of the lowest excited state slows down for the larger fullerenes. This trend in dynamics, monitored throughout the visible and NIR range, is found to correlate with the number of isomers in accordance with the isomerization mechanism suggested by Stone and Wales. The Stone−Wales isomerization was calculated as thermally inaccessible but photoinduced barrierless. The energy difference of the isomers is in the 1 meV range, and back-isomerization is observed on the picosecond time scale. The characteristic spectrally broad transient absorption of the investigated fullerenes is promising for fast optical gating applications.

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