UV resonance raman and UV-VIS absorption spectra of aqueous solutions of an azobenzene-containing ammonium amphiphile

Abstract

UV resonance Raman and UV-VIS absorption spectra of aqueous solutions of an azobenzene-containing, single-chain amphiphile have been measured over wide ranges of temperature and concentration. Below the gel- or coagel-liquid crystalline phase transition temperature ( T c), the aqueous solution gives a doublet absorption band at 375 and 393 nm due to a J-like bilayer aggregate. Above T c, on the other hand, it shows a single broad band at 345 nm suggesting the liquid crystalline state. With a further increase in temperature, the absorption band shifts to 355 nm, indicating that a molecularly dispersed state is attained. The intensity ratios of the two intense Raman bands at 1458 and 1413 cm −1 of the aqueous solution are found to change upon the melting of ice surrounding the amphiphile. With dilution of the aqueous solution below and above T c, spectral changes due to the gel-molecularly dispersed state transition and the liquid crystalline-molecularly dispersed state transition are observed at 2 x 10 −5 and 4 x 10 −5 M, respectively.