Twisting and bending photo-excited phenylethynylbenzenes - a theoretical analysis

Oligo(phenylethynyl)benzenes are a family of compounds that exhibit a rich photochemistry changing dramatically with different orientation of a phenyl group in the molecule. Quantum-chemical calculations have been performed to investigate different members of this family of compounds and compared to previous experimental and theoretical studies. 1,4-Bis(phenylethynyl)benzene (BPEB) has different optical properties than its smaller relative diphenylacetylene; however, upon twisting an outer phenyl ring of BPEB, its photochemistry becomes very similar. Fluorine substituents at the central benzene ring are shown to have only small effects on the optical properties of BPEB. Phenylethynylbenzenes exhibit a rich photochemistry changing dramatically with different ring orientation, as quantum-chemical calculations reveal for 1,4-bis(phenylethynyl)benzene showing different optical properties than its smaller relative tolan.