Donor–acceptor–acceptor (D–A–A) type 1,8-naphthalimide based small molecules SM1 and SM2 functionalized with tetracyanobutadiene (TCBD) and dicyanoquino-dimethane (DCNQ) modules, showing strong absorption in the visible and near-infrared (NIR) region are reported. TCBD and DCNQ linked SM1 and SM2 exhibit multi-redox waves. The electrochemical and optical HOMO–LUMO gaps show similar trends. These SMs exhibit a broad absorption profile which is complementary to the D–A copolymer P donor and also possess an appropriate lowest unoccupied molecular orbital (LUMO) to serve as an acceptor with P with a LUMO level of −3.33 eV. The organic solar cells based on P:SM1 and P:SM2 exhibit a PCE of 4.94% and 6.11%, respectively. The higher value of the PCE for the SM2 based organic solar cells has been attributed to the broader absorption profile, more balanced charge transport and lower photon energy loss. The values of V_oc of the organic solar cells for the SM1 acceptor (1.06 V and 1.02 V without and with solvent additive) are the highest values reported for devices based on non-fullerene acceptors to the best of our knowledge. The energy loss (E_loss) of 0.56 eV and 0.48 eV for SM1 and SM2 based devices, respectively is one of the smallest reported for BHJ organic solar cells.

This article reports the design and synthesis of donor-substituted symmetrical and unsymmetrical benzothiadiazoles (BTDs) 5–12 of type D–π–A–D, D₁–π–A–D₂, D₁–A₁–A₂–D₂, D–A₁–A₂–D and D–A₁–A₂–A₁–D by Ullmann, Suzuki and cycloaddition–retroelectrocyclization reactions. The photophysical, electrochemical and computational properties were studied and show substantial donor–acceptor interaction. Their single photon absorption show strong charge transfer bands in the near-infrared (NIR) region and the electrochemical reduction show multiple reduction waves. The optical HOMO–LUMO gap of BTDs 5–12 was found to be a function of the number and nature of the acceptors. Computational studies reveal that strong cyano-based acceptors, dicyanoquinodimethane (DCNQ) and tetracyanobutadiene (TCBD) lower the LUMO level in BTDs 7–12, which results in a low HOMO–LUMO gap compared to acetylene linked BTDs 5 and 6. The BTDs with carbazole and single TCBD and DCNQ acceptors show better thermal stability.

A series of donor–acceptor ferrocenyl substituted BODIPYs have been designed and synthesized via palladium catalyzed Suzuki and Sonogashira coupling reactions. The UV-visible absorption results indicate intramolecular charge transfer from the ferrocene to the BODIPY. The fluorescence quantum yield was drastically reduced, where the ferrocenyl group was directly attached to the BODIPY. The single crystal X-ray structures of 1′, 2, 3, and 4 show marvelous supramolecular interactions. The crystal structure of 1′ shows an extensive hydrogen bonded 2D network, 2 shows sheet like structure, 3 shows zigzag packing along the a-axis, whereas 4 shows sheet like structure in which both the surfaces of the sheet are covered with the ferrocenyl group.

A set of donor–π-acceptor–π-donor type ferrocenyl substituted BODIPYs were designed and synthesized by the Sonogashira coupling reaction. These compounds exhibit red shifted absorption and poor fluorescence. The electrochemical properties of these compounds exhibit strong donor–acceptor interactions. The crystal structure of 3b exhibits an extensive hydrogen bonded 2-D network.