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ESR measurements on 9, 10-diphenylanthrace in solution show that the molecule is non-planar, the two phenyl rings being twisted by about 66° relative to the anthracene nucleus. This agrees with previous predictions made on the basis of scale models. Evidence from absorption and fluorescence spectra for a change of angle between ground and excited state is examined, and a decrease of about 6° is found for the excited state. On the basis of the large angle of twist possible reasons are suggested for the difference between anthracene and 9, 10-diphenylanthracne with regard to dimer formation and quantum yield of fluorescence in solution.