Structures and Photophysical Properties of Model Compounds for Arylethylene Disilylene Polymers

The compounds [C 6 H 5 C⋮CC 6 H 4 C⋮CSiR 2 ] 2 (R = Me ( 3a ), n -Bu ( 3b )) have been synthesized by the reaction of C 6 H 5 C⋮CC 6 H 4 I with HC⋮CSiR 2 SiR 2 C⋮CH. The structures of [C 6 H 5 C⋮CSi(CH 3 ) 2 ] 2 ( 2 ), 3a, and C 6 H 5 C⋮CC 6 H 4 C⋮CC 6 H 5 ( 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.