Photophysical characterization and effect of pH on the twisted intramolecular charge transfer fluorescence of trans-2-[4-(dimethylamino)styryl]benzothiazole

Defining the different phases of premicellar aggregation using the photophysical changes of a surface-probing compound

“…The TICT fluorescence of DMASBT in the polar medium has already been explained by Saha et al [12]. From the above discussion it thus becomes clear that the probe molecule is likely to be pushed outward toward the surface when micelles are formed.…”

“…After the formation of the micelles, the fluorescence band becomes broad and structureless and undergoes a red shift. It is known that TICT fluorescence of DMASBT occurs with peak position in the range between 480 and 520 nm in polar solvents of varying polarities [12]. Therefore, it can be stated here that when micelles are formed, the DMASBT molecule may be somewhat pushed out to the surface from the hydrophobic region due to the interaction between its dipole and the surface charges of the micelles.…”

“…The bands are structured in this concentration range. In our previous study [12] it was observed that DMASBT demonstrates LE fluorescence in nonpolar solvents, giving structured fluorescence bands at ∼450 nm and broad structureless TICT fluorescence bands at ∼510 nm in polar solvents. Evolution of structured fluorescence bands at ∼490 nm at lower concentrations of CTAB suggests that DMASBT molecule is residing neither in a very hydrophobic region nor in a highly polar region but in a region with intermediate polarity that probably favors the LE fluorescence to some extent.…”

“…due to the alignment of the benzothiazole moiety toward water, which causes greater stabilization of the TICT state and thereby quenching of TICT fluorescence due to the increase in the nonra- diative decay processes as a result of closer proximity of the TICT state to the triplet state as well as to the ground state [12,20].…”

“…This compound could act as a surface probe to monitor the formation of premicellar aggregates at different concentrations of cationic (cetyltrimethylammonium bromide, CTAB), anionic (sodium dodecyl sulfate, SDS), and neutral (Triton X-100, TX-100) surfactant molecules. DMASBT shows dual fluorescence [12,13]. The shorter wavelength band at ∼450 nm is the locally excited (LE) band and the longer wavelength band at ∼520 nm is the TICT band.…”