TOWARDS A HOMOLOGOUS STRUCTURAL SERIES OF SOLVATOCHROMIC PI-ASTERISK INDICATORS

Two new pi indicators of solvent dipolarity and polarizability were s ynthesized and characterized with respect to their solvatochromic and acid-base properties, The new dyes, N,N-dipropyl-p-nitroaniline and N, N dibutylp-nitroaniline, are part of a homologous structural series of indicators with increasing lipophilic character, ranging from N,N-dim ethyl-p-nitroaniline to N,N-dibutyl-p-nitroaniline. The new indicators are designed as specific polarity probes for the characterization of aqueous-organic interfacial systems, Visible absorption spectra for N, N-dipropyl-p-nitroaniline and N,N-dibutyl-p-nitroaniline show solvent- dependent bandshapes in a manner similar to that of the previously cha racterized diethyl species, Values of -s decrease slightly from N,N-di ethyl-p-nitroaniline to N,N-dipropyl-p-nitroaniline, leveling off with increasing alkyl chain length, The trend in pK(BH+) for the p-nitroan ilinium ions over the range from N,N-dimethyl- to N,N-dibutyl- is cons istent with known trends for the corresponding anilinium ions.