Platinum–Acetylide\nComplexes as Nonfullerene\nAcceptors in Organic Photovoltaic Systems

Three distinct n-type semiconductors were derived from\na platinum-trialkyl\nphosphine complex; to lower their LUMO levels, various indene derivatives\nwere incorporated using thiophene (PtTIC (<b>1</b>)), thieno[3,2-<i>b</i>]thiophene (PtT2IC (<b>2</b>)), and 4<i>H</i>-cyclopenta[2,1-<i>b</i>:3,4-<i>b</i>′]dithiophene\n(PtCDTIC (<b>3</b>)) as the acetylide donor units. Single-crystal\nX-ray diffractometry analysis revealed translinear platinum–acetylide\ncomplexation in all cases. The strong (O···S)\ninteractions between the oxygen atoms of the indene acceptor units\nand the sulfur atoms of the thiophene-derived donor units induced\na highly planar orientation among the heterocyclic ligands, featuring\nπ–π interactions between the planes. Platinum complexes <b>1</b>, <b>2</b>, and <b>3</b> exhibited strong absorption\nin the 500–800 nm range, resulting from efficient intramolecular\ncharge transfer transitions from the central platinum-containing donor\nunit to the terminal acceptors, as well as unique emission in the\nnear-infrared region owing to the heavy-atom effect. The ultraviolet\nphotoelectron spectroscopy results indicated that the LUMO levels\nwere comparable to those of typical nonfullerene acceptors (NFAs).\nThe n-type semiconductors comprising <b>1</b>, <b>2</b>, and <b>3</b> as NFAs exhibited photoelectric conversion properties\nin the corresponding organic photovoltaics. The highest conversion\nefficiency (3.0%) was attained by complex <b>3</b>.