Platinum–Acetylide Complexes as Nonfullerene Acceptors in Organic Photovoltaic Systems

Three distinct n-type semiconductors were derived from a platinum-trialkyl phosphine complex; to lower their LUMO levels, various indene derivatives were 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 (PtCDTIC (<b>3</b>)) as the acetylide donor units. Single-crystal X-ray diffractometry analysis revealed translinear platinum-acetylide complexation in all cases. The strong (═O···S) interactions between the oxygen atoms of the indene acceptor units and the sulfur atoms of the thiophene-derived donor units induced a highly planar orientation among the heterocyclic ligands, featuring π-π interactions between the planes. Platinum complexes <b>1</b>, <b>2</b>, and <b>3</b> exhibited strong absorption in the 500-800 nm range, resulting from efficient intramolecular charge transfer transitions from the central platinum-containing donor unit to the terminal acceptors, as well as unique emission in the near-infrared region owing to the heavy-atom effect. The ultraviolet photoelectron spectroscopy results indicated that the LUMO levels were comparable to those of typical nonfullerene acceptors (NFAs). The n-type semiconductors comprising <b>1</b>, <b>2</b>, and <b>3</b> as NFAs exhibited photoelectric conversion properties in the corresponding organic photovoltaics. The highest conversion efficiency (3.0%) was attained by complex <b>3</b>.