Absence of HOMO/LUMO Transition in Charge-Transfer Complexes of Thienoacenes

In charge-transfer complexes, transition from the donor highest occupied molecular orbital (HOMO) to the acceptor lowest unoccupied molecular orbital (LUMO) gives the charge-transfer absorption. However, in tetracyanoquinodimethane (TCNQ) complexes of thienoacenes, comparison of the observed and calculated charge-transfer absorption demonstrates that the HOMO/LUMO transition is absent in the solid state owing to the orbital symmetry, and the first near-infrared band comes from the transition from the donor next HOMO to the TCNQ LUMO. Maps of the oscillator strength in rotated and translated molecular geometries are calculated on the basis of the time-dependent density functional theory, in which the absence of the HOMO/LUMO transition is approximately maintained even in the general molecular geometry.