Synthesis and photophysical study of D-π-A-π-D chromophores based on triphenylamine and isoindigo, benzothiadiazole and diketopyrrolopyrrole acceptor cores for optoelectronics

The synthesis of three small molecules with an electronic quadrupolar D-π-A-π-D architecture based on triphenylamine (TPA) as the terminal donor moiety bonded to derivatives of the diketopyrrolopyrrole (DPP), benzothiazole (BT), and isoindigo (II) as acceptor moieties, are reported. The synthesised molecules exhibit similar optical absorption properties within the 300–700 nm range, with maxima experimental absorption in film at 479 nm (BT-TPA), 483 nm (DPP-TPA), and 468 nm (II-TPA). The optical bandgap (Egapfilm) values were determined as 1.83, 1.96, and 1.98 eV for BT-TPA, DPP-TPA and II-TPA, respectively; indicating a slight variation in electronic properties among the compounds. Cyclic voltammetry measurements revealed frontier molecular orbital (FMO) energy levels of −4.79, −4.70, and −4.93 eV (Higher Occupied Molecular Orbital, HOMO) and −2.85, −2.79, and −2.79 eV (Lower Unoccupied Molecular Orbital, LUMO) for BT-TPA, DPP-TPA, and II-TPA, respectively. These values align with the energetic requirements for hole-transport layers in perovskite solar cells. The results confirm the electronic properties, intramolecular interactions and the potential for forming a stable quinoid-radical structure; further supported by DFT and TD-DFT calculations. Future studies will evaluate their stability under operating conditions, integrate them into perovskite solar cell architectures and optimise manufacturing conditions to maximise photovoltaic performance.