Steady-state and time-resolved fluorometric techniques have been exploited to study the photophysical and distribution behavior of an efficient
cancer cell
photosensitizer,
norharmane (NHM), in well-characterized, biomimicking nanocavities formed by cationic
micelles with varying
surfactant chain length. Amphiphiles like dodecyl trimethyl
ammonium bromide (
DTAB), tetradecyl trimethyl
ammonium bromide (TTAB), and cetyl trimethyl
ammonium bromide (
CTAB) have been used for the purpose. Emission behavior of NHM is very much dependent on the
surfactant concentration as well as their hydrophobic chain length. The binding constant (K) and free-energy change (DeltaG) for the interaction of NHM with the cationic
micelles have been determined from the fluorescence data. Polarity of the microenvironment around the probe has been determined in the cationic micellar environments from a comparison of the variation of fluorescence properties of the two-prototropic species of the probe in water/
dioxane mixture with varying composition. Experimental results demonstrate that the variation in the cationic
surfactant chain length plays an important role in promoting a specific prototropic form of the probe molecule. Fluorescence decays are biexponential in all the
micelles indicating that the probe molecules are distributed between the two distinct regions of the
micelles. The population of the component with a longer lifetime corresponds to the probe in the head group site, while the short-lived component comes from the probe bound to the core region of the
micelles. On the basis of the lifetime measurements, the partitioning behavior of the chromophore in the head group and in the core regions in the
micelles has been determined.