Spectroscopic study of harmane in micelles at 77 K using fluorescent probes

Steady-state and time-resolved emission for spectroscopic techniques at 77 K, and molecular orbital calculations using PM3 MOPAC/93 and HAM/3-CI have been used to study the two forms of harmane, the neutral (HN) and the monop rotonated (HH), in different environments. In hydrophobic media, for (HN), four species were determined and in hydrophilic medium, for (HH), we found just one species. The photophysical properties of all these species were de termined, and we verified that each one of them displays distinct photophys ical properties from one to another. For example, for monomer of(HN), the l owest electronic singlet state S-1 is (pi, pi*) and the lowest electronic t riplet state T-1 is (pi,pi*), due to the phosphorescence lifetime it is t = 0.8 s. For the (HH) monomer, the S-1 is (pi,pi*) and T-1 is in, (pi,pi*) a nd the spin-orbital coupling is inefficient. These determinations were used to characterise and to identify the harmane species that is solubilised in to the interior of neutral (triton X-100), anionic (dodecyl lithium sulphat e) and cationic (hexadecyltrimethyl ammonium bromide) micelles, all of them were prepared under physiological conditions. The results indicated that a ctive species in the interior of the micelles is a hydrogen bond complex be tween (HN) and micellar environments that is anchored in the aqueous region of micelles. (C) 2000 Elsevier Science Ltd. All rights reserved.