Fluorescence Probe Studies of Anthracene and 9-Methylanthracene in Detergent Micelles

Abstract

The photophysical properties of anthracene and 9-methylanthracene have been investigated in a variety of solvents and the resulting information used to interpret data after incorporation of the two fluorophores into aqueous solutions comprising Triton X-100, cetyltrimethylammonium bromide (ctab) or sodium dodecyl sulfate (sds) micelles. The fluorescence probe methods used to elucidate micellar properties such as microviscosity , micropolarity, and the permeability of the micelle/water interface to aromatic molecules and ions, included steady-state polarization, time-resolved anisotropy and steady-state and lifetime quenching techniques. NN- Dimethylaniline (dma) and I-ions were shown to partition into Triton X-100 micelles with partition coefficients, K_p, of about 70 and 51, respectively. Excimer formation between dma and the two probes was not observed in Triton X-100 micelles, these results indicating high micropolarities (E ≈30) and microviscosities ; from polarization and anisotropy measurements the microviscosity was in the range 60-156 cP . In contrast, excited-state complexation was observed in ctab and sds. For anthracene in ctab, triplex formation occurred with an equilibrium constant, K_c, of 137 dm³ mol^-l. Weak ground-state complexation between I^- and the two probes was also observed in Triton X-100 and ctab micelles with equilibrium constants, K_c, in the range 0.36-9.6 dm³ mol^-l. The importance of probe characterization is highlighted by the results in sds where multiple-site occupancy occurred.