Structures and Photophysical Properties of Model Compounds for Arylethylene Disilylene Polymers

Abstract

The compounds [C6H5C⋮CC6H4C⋮CSiR2]2 (R = Me (3a), n-Bu (3b)) have been synthesized by the reaction of C6H5C⋮CC6H4I with HC⋮CSiR2SiR2C⋮CH. The structures of [C6H5C⋮CSi(CH3)2]2 (2), 3a, and C6H5C⋮CC6H4C⋮CC6H5 (4) have been determined by a single-crystal X-ray diffraction. In 3a and 4 short contact distances between the aryl rings and the acetylene groups (3.587 (3) Å in 3a and 3.481 (2) Å in 4) indicate strong intermolecular interactions in the solid state. The fluorescence spectra of diphenylacetylene, 3a, 3b, and 4 are highly dependent on concentration. In dilute solution (around 10-6 mol/L), spectra appear to be of single molecules, but at higher concentration, a red shift was observed, assigned to excimer formation. At still higher solid-state concentrations or in crystals, a further red shift for 3a and 4 was evident, probably due to the formation of aggregates.