Lowest singlet exciton in pentacene: modern calculations versus classic experiments

Based on simple model calculations, the expected magnitude of the field-induced shift observable in electroabsorption is estimated for three alternative assignments proposed in the literature for the lowest singlet excitation of the pentacene crystal (pure Frenkel exciton, pure charge-transfer exciton, or a mixture of both). The results are compared with the corresponding experimental value, which is also known from the literature. The latter turns out to be compatible only with the mixed parentage of the pertinent state, which contains the charge-transfer contribution in the range from 25 to 70%. The conclusion is discussed in the context of the present controversies concerning the existing experimental and theoretical evidence on this subject.