Singlet and triplet exciton bands

Tig.1. The first singlet and triplet exciton bands of the polydiacetylene PTS shown together with the original electron and hole polaron bands. 

Singlet and triplet exciton bands are distinguished by substituting in relation (8.20) not Wannier spin orbitals but only Wannier functions with spatial dependence. The only difference compared to equation (8.20) will be that, before its second term (the exchange term), one has to insert a factor 2Sm, where <5m = 1 in the singlet case and = 0 in the triplet case. 

TABLE 8.3. Singlet and Triplet Exciton Bands, E(K and the Corresponding Oscillator Strengths, /, Obtained for the a-Helical Polypeptide Backbone (energies in eV after Suha ... 

FIGURE 22.4 Energy levels, optical transitions, and emission bands associated with singlet and triplet excitons and PP excitations, respectively. The symbols lAg, IBu, mA, and BX are the ground state, lowest allowed exciton, most strongly coupled even-parity exciton, and biexciton level, respectively T is the lowest triplet level Full and... 

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. 

---