Development of bis(arylimino)acenaphthene (BIAN) copper complexes as visible light harvesters for potential photovoltaic applications

Photovoltaics with dye-sensitized solar cells have been recognized as being promising for the utilization of sunlight to produce electricity and 'solar chemicals'. One of the remaining unsolved challenges is the development of an affordable, robust dye that has a panchromatic light harvesting range and efficiently provides separated charges for the desired photochemistry. The most commonly employed molecular photosensitizers include the noble metal-based ruthenium and iridium complexes, synthetically challenging porphyrin derivatives, and expensive, functionalized polypyridine compounds. Here, we describe the development of Cu(i) dyes supported by bis(arylimino)acenaphthene (Ar-BIAN) ligands, which can be synthesized in fewer than three steps from affordable, commercially available reagents. The diamagnetic, homoleptic complexes have been characterized by a suite of spectroscopic and analytical methods and exhibit panchromatic light absorption extending to the near infrared (NIR) region. Remarkably, the crystal structure of a complex bearing an ortho-iodoarylimino substituent displays a unique, rhombically distorted square planar geometry around the Cu(i) center, for crystals isolated from two disparate solvent combinations. Density functional theory (DFT) calculations were performed to provide insights into the spectroscopic features and the unusual coordination sphere around the metal center, and allude to non-covalent interactions between the aromatic groups and among the iodide atoms. Preliminary studies were conducted to explore the application of these copper photosensitizers in dye-sensitized solar cells.