Evidence for at least Two CMC's : Studies by Excited State Proton Transfer of Carbazole and Twisted Intramolecular Charge Transfer of N,N-dimethylaminobenzonitrile

Micellisation of three surfactants, namely, cetyltrimethylammonium bromide (CTAB), triton X-100 (TX) and sodiumdodecylsulphate (SDS), in aqueous solutions, has been studied by the excited state proton transfer (ESPT) of carbazole (CAZL) as well as the twisted intramolecular charge transfer (TICT) of N,N-dimethylaminobenzonitrile (DMABN). The critical micellar concentrations (CMC's) of the aqueous micellar systems have been determined by measuring the relative intensity of the neutral to the anionic species (N/A) of the probe (CAZL) or the excited state lifetime of the neutral species (τ₃₆₀) in the former study. They have also been determined independently probing the relative yield of the charge transfer emission to the locally excited (LE) emission (φ_TICT/φ_LE) of DMABN in the latter study. The experimental results reveal that there exist at least two CMC's for all the three aqueous micelles in spite of the fact that the individual micellar units have different surface electrical properties.