Effects of various heteroatom donor species on the photophysical, electrochemical and photovoltaic performance of dye-sensitized solar cells

Band Gap Engineering in Acceptor-Donor-Acceptor Boron Difluoride Formazanates

π-Conjugated molecules with acceptor-donor-acceptor (A-D-A) electronic structures make up an important class of materials due to their tunable optoelectronic properties and applications in, for example, organic light-emitting diodes, nonlinear optical devices, and organic solar cells. The frontier molecular orbital energies, and thus band gaps, of these materials can be tuned by varying the donor and acceptor traits and π-electron counts of the structural components. Herein, we report the synthesis and characterization of a series of A-D-A compounds consisting of BF₂ formazanates as electron acceptors bridged by a variety of π-conjugated donors. The results, which are supported by density functional theory calculations, demonstrate rational control of optoelectronic properties and the ability to tune the corresponding band gaps. The narrowest band gaps (E_g^Opt = 1.38 eV and E_g^CV = 1.21 eV) were observed when BF₂ formazanates and benzodithiophene units were combined. This study provides significant insight into the band gap engineering of materials derived from BF₂ formazanates and will inform their future development as semiconductors for use in organic electronics.