STRUCTURES AND PHOTOPHYSICAL PROPERTIES OF MODEL COMPOUNDS FOR ARYLETHYLENE DISILYLENE POLYMERS

The compounds [C6H5C=CC6H4C=CSiR2](2) (R = Me (3a), n-Bu (3b)) have be en synthesized by the reaction of C6H5C=CC6H4I with HC=CSiR2SiR2C=CH. The structures of [C6H5C=CSi(CH3)(2)](2) (2), 3a, and C6H5C=CC6H4C=CC6 H5 (4) have been determined by a single-crystal X-ray diffraction. In 3a and 4 short contact distances between the aryl rings and the acetyl ene groups (3.587 (3) Angstrom in 3a and 3.481 (2) Angstrom in 4) indi cate strong intermolecular interactions in the solid state. The fluore scence spectra of diphenylacetylene, 3a, 3b, and 4 are highly dependen t on concentration. In dilute solution (around 10(-6) mol/L), spectra appear to be of single molecules, but at higher concentration, a red s hift was observed, assigned to excimer formation. At still higher soli d-state concentrations or in crystals, a further red shift for 3a and 4 was evident, probably due to the formation of aggregates.