Quinoidal Acenedichalcogenophenediones for Near-Infrared-Absorbing Organic Semiconductors: Effects of Chalcogen Atom Substitution on the Physicochemical and Carrier Transport Properties

To develop near-infrared (NIR) absorbing organic semiconductors via the donor-acceptor approach, a highly electron deficient acceptor unit that lowers the LUMO energy level is important to reduce the optical energy gap while keeping its low-lying frontier orbital energy levels. Here, we synthesized and investigated donor-acceptor-donor (D-A-D) triad molecules incorporating two isoelectronic series of benzo[1,2-b:4,5-b']dichalcogenophene-2,6-diones and naphtho[1,2-b:5,6-b']dichalcogenophene-2,7-diones having different chalcogen atoms, namely, oxygen, sulfur, and selenium atoms. Optical and electrochemical measurements revealed that the triad molecules have low-lying HOMO and LUMO energy levels below -5.0 and -4.0 eV, respectively, with small optical energy gaps of down to 0.76 eV. The key structural feature for the small optical energy gaps is the carbonyl-terminated p-quinodimethane and 2,6-naphthoquinodimethane skeletons in the acenedichalcogenophenediones, which facilitate intramolecular charge transfer from the donor to acceptor units regardless of the chalcogen atoms. On the other hand, the field-effect hole and electron mobilities of the thin-film transistor devices based on the oxygen analogues (similar to 10(-1) cm(2) V-1 s(-1)) were one order of magnitude higher than those of the sulfur and selenium analogues (similar to 10(-2) cm(2) V(-1)s(-1)). Systematic investigation of the crystal structures, thin-film microstructures, and melting points as well as theoretical calculations revealed that the oxygen analogues have significantly high coplanarity and rigidity of the DA-D p-conjugated backbone resulting in the low structural and/or energetic disorder in the solid state, which is a reason for the superior carrier transport properties to those of the sulfur and selenium analogues. These molecular insights are helpful for the development of superior donor-acceptor NIR-absorbing organic semiconductors.

Automated summary

By synthesizing and studying D-A-D triad molecules using the donor-acceptor approach, it was found that a highly electron deficient acceptor unit lowers the LUMO energy level, reduces the optical energy gap, and maintains low-lying frontier orbital energy levels. Two isoelectronic series incorporating different chalcogen atoms were investigated, and the oxygen analogues exhibited superior carrier transport properties compared to the sulfur and selenium analogues.