New Probes for Surfactant Solutions: Phosphorescent Labelled Detergents

A series of alkyltrimethylammonium bromides containing terminal phosphorescent chromo-phores have been prepared and characterized. 10-(4-bromo, l-naphthoyl)decyltrimethylammonium bromide(BND–10) has a critical micelle concentration (CMC) of 14 mM and a micellar mean aggregation number () of 105. Analogous detergents,BND–11, -8, and -5 have also been prepared; in each case, the naphthoyl group is located at the terminal carbon of an alkyl chain of the indicated length. The normal behavior of increasing and decreasing CMC with increasing aliphatic chain length is observed. When compared with unsubstituted alkyltrimethylammonium bromides, the 4-bromo, 1-naphthoyl chromo-phore is roughly equivalent to 6 methylenes with respect to hydrophobic contribution. A broad phosphorescence maximizing at about 590 nm is readily detected upon photoexcitation of the BND molecules in various solvents. The weak fluorescence of the probes is consistent with efficient intersystem crossing of the BND molecules. BND–10 has a phosphorescence yield of 0.023 and a lifetime of 1 ms in water at 250C. The probes are useful for the study of micelle-detergent exchange dynamics.