Nanosecond time-resolved infrared spectroscopy has been used to study the structure and dynamics of the excited electronic states of 4-(dimethylamino)benzonitrile (DMABN) in polar and nonpolar solvents. In a polar solvent butanol, two distinct transient species were observed. The first species with a few nanosecond lifetime has been identified as the twisted-intramolecular-charge-transfer (TICT) singlet excited state and the second species having an oxygen-sensitive lifetime as the TICT triplet state of DMABN. Both the singlet and triplet TICT states show large downshifts (> 120 cm(-1)) of the C=N stretch frequency, indicating that the charge transfer has a significant effect on the structure of the cyano group. In a nonpolar solvent hexane, only one transient species was detected. This species has been assigned to the non-CT triplet excited state of DMABN from the observed oxygen quenching effect.