DTT-DDQ Mixed-Stack Organic Charge-Transfer Crystals with Near-Infrared Absorption

Dithieno[3,2-b:2′,3′-d]thiophene (DTT) is a common molecular motif in organic electronics. We find that it forms a 1:1 charge-transfer complex (CTC) with the electron acceptor 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). The 1:1 complex has an alternating donor/acceptor mixed-stack structure, and an intense near-infrared absorption band. Vibrational spectroscopy and electronic structure calculations are used to further understand the partial ionization induced by the DTT/DDQ complex.