Picosecond transient infrared spectra of diphenylacetylene (DPA) were obtained in cyclohexane and acetonitrile solutions for the 1640-940 cm(-1) wavenumber region, using a method based on optically heterodyned detection of absorption anisotropy. The observed transient species was assigned to the S-1 state of DPA on the basis of its temporal behavior. Comparison with the reported CARS spectra suggests that S-1 DPA has a planar(probably trans-bent) structure with a center of symmetry in both solutions.