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) Angstrom in 3a and 3.481 (2) Angstrom 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.