Anthracene triplet exciton band

As shown by Choi et al. (40) contributions of ionized states and of the exchange interaction to the width of triplet excitonic band are of the same order of magnitude. When ionized states are taken into account, the Davydov splitting in anthracene and naphthalene increases by about 50%. 

Fig. 6.11 Calculated exciton band structure of the T] state of anthracene for three directions in the reciprocal lattice. The experimentally-determined numerical values for the triplet resonance interactions are given in the text (from [19]). The dashed curve is a typical dispersion relation for acoustic phonons in anthracene [28].

The theoretical prediction, for aromatic hydrocarbons (the only ones now available) are as follows . Ionic-exciton states will contribute mainly to neutral excitons of small band width that is, singlet excitons which correspond to weak transitions and triplet excitons. Ionic contributions may broaden the exciton-band widths and may be particularly important in enhancing the rates of triplet-energy migration. A spectroscopic study of anthracene indicates the ionic exciton lies energetically above the first singlet level. No undisputed direct experimental detection of an ionic-exciton level in a one-component organic crystal has yet been made. 

---