Spectral and photophysical properties of the alkaloid berberine (B) were studied in solvents with different solvent parameters, using UV/Vis absorption, emission and excitation spectroscopy. The absorption and emission maxima were found to be between 421-431 nm and 514-555 nm, respectively, leading to Stokes' shifts between 4099 and 5735 cm(-1). The fluorescence quantum yields varied between 10(-2)-10(-4), depending on the solvent. Different solvent scales have been used to study the solvatochromism of B. Linear solvation energy relationships (LSER) proposed by Kamlet-Taft suggest that B is a molecule attractive as a probe for solvent polarity and hydrogen bonding properties.

Singlet oxygen (O 2 ( 1 ∆ g )) production and quenching in homogeneous and microheterogeneous media are reported for two anionic ruthenium(II) complexes ([RuL 2 L′] 2-(where L stands for (1,10-phenanthroline-4,7-diyl)bis-(benzenesulfonate) (pbbs) and L′ stands for N- (1,10-phenanthrolin-5-yl)acetamide (paa) or N-(1,10phenanthrolin-5-yl)tetradecanamide (pta)) and for the cationic complex [Ru(bpy) 3 ] 2+ (bpy: 2,2′-bipyridine). Comparative results of photosensitized 1 O 2 generation in micelles, reverse micelles, and microemulsions reveal that the nature of the ligands and the size and charge of the [RuL 3 ] complexes are important factors affecting their effective location and 1 O 2 production in these media. The rate constants of quenching of the excited state [RuL 3 ]* by molecular oxygen (k q ) are in the range of (1-3) × 10 9 M -1 s -1 . The emission lifetimes of [RuL 3 ]* and k q values depend on the nature of the ligand and on the medium. The complexes are stable singlet oxygen sensitizers, with quantum yields of singlet oxygen production (Φ ∆ ) in air-equilibrated solutions between 0.30 and 0.75. The efficiency of 1 O 2 formation (i.e., the fraction of triplet excited states quenched by oxygen yielding 1 O 2 , f ∆ T ) is a valuable probe of the interactions of the [RuL 3 ] complexes with micelles and microemulsions. The highest f ∆ T values (g0.90) were observed in micellar media based on surfactants bearing a charge opposite to that of the [RuL 3 ] complex. In the microheterogeneous systems investigated, the most probable location of the [RuL 3 ] sensitizers is the micellar interfacial region.

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The influence of solvent polarity on the dye-sensitized photooxidation (singlet molecular oxygen (O2(1Δg)) mediated) of a series of para-substituted phenolates was studied. Kinetic evidence obtained shows that the overall and the pure chemical interactions, phenolate–O2(1Δg), depend on the solvent polarity in a different way. This is clearly reflected in the efficiency of O2(1Δg) photooxidation of the substrates: surprisingly, the photooxidation quantum yield increases as the overall quenching rate constant decreases. The substrate photooxidation quantum yields obtained ranged from 0.05 to 0.15, the upper limit corresponding to a moderately polar medium (a benzene–methanol mixture) and the lower to an aqueous medium. We conclude that a high solvent polarity favours only the obtainment of the encounter complex (O2(1Δg)–phenolate), whereas the reactive step is affected in much the same way as those processes where charges are neutralized along the reaction pathway. The results obtained are discussed in terms of a partly polar excited state complex between O2(1Δg) and the phenolates. The rate constant for the reactive pathway in both organic and aqueous media is correlated with the Hammet-type substituent constant R−.