Solvent-sensitive probes have wide application in the study and characterization of interfacial systems. This work presents some new, more hydrophobic versions of the solvatochromic pi* indicators of solvent dipolarity-polarizability. The new dyes form a homologous series of N,N-dialkyl-p-nitroanilines. The indicators are designed to act as improved probes of micelles and lipid bilayers in polar and aqueous solutions. UV-vis studies of the N,N-dipentyl- and N,N-dihexyl-p-nitroanilines show the two indicators to be strongly solvatochromic; Values of -s estimated from two-point correlation are 3.081 and 3.110, respectively. W-vis spectra of N,N-dipentyl- and N,N-dihexyl-p-nitroanilines obtained at variable indicator concentration in cyclohexane and dimethyl sulfoxide, within the 10(-5) M concentration range, display no concentration-dependent spectral shifting and no evidence of indicator aggregation in accordance with Beer＇s law. Studies of the indicator series in aqueous solutions of varying concentration of the anionic surfactant sodium dodecyl sulfate (SDS) suggest that N,N-dipropyl-p-nitroaniline probes micelles of SDS more deeply than the commonly used N,N-dimethyl- and N,N-diethyl-p-nitroanilines. Of the three indicators in the series, N,N-dimethyl-, N,N-diethyl-, and N,N-dipropyl-p-nitroaniline, the dipropyl species is most responsive to the critical micelle concentration of SDS. The longer chain dyes N,N-dibutyl-, N,N-dipentyl-, and N,N-dihexyl-p-nitroaniline are more effective probes of larger micelles of the nonionic surfactant Triton X-114. UV-vis studies of N,N-dihexyl-p-nitroaniline in micellar solutions of Triton X-114 and model systems suggest that the longest chain indicator probes the outer polyoxyethylene portion of the Triton X-114 micelle.