Electric field induced transition in the charge-transfer exciton band of anthracene-PMDA

A second, electric field induced zero-phonon transition has been observed in single crystals of anthracene-PMDA (pyromellitic acid dianhydride). The second transition is 10 cm^?1 above the lowest zero-phonon absorption; its intensity increases with increasing field strength under conservation of oscillator strength for the two transitions. The measured splitting of 10 cm^?1 is interpreted in terms of the charge-transfer exciton bandwidth. The measured field-shift gives an approximate value Δμ for the change in dipole moment which characterizes the creation of an ionic charge-transfer state.