The photoinduced polymerization of acrylic monomers using dyes in a protein-restricted medium is reported. We studied dyes of different families as potential polymerization catalysts, exploiting the observation that the photophysical properties of some dyes are altered when bound to biopolymers. The light induced polymerization of acrylic monomers in the presence of bovine serum albumin or gelatin using triphenylmethane and azo dyes proceeded smoothly. Using GE Miser 120 W spotlights as a convenient illumination source, we found polymerization could be achieved in some cases within 60 min of irradiation. The polymerization rates were found to be dependent on the concentrations of the dye and the protein. In the absence of protein or dye polymerization was virtually non-existent. When the reaction mixture was blanketed with nitrogen, polymerization was observed to be faster than that that in air equilibrated samples. We believe these photopolymerizations may proceed via a free-radical pathway. Our results suggest the possible role of some of these dyes as polymerization catalysts, though they had previously seemed inert in fluid solutions.

The photocatalytic bleaching of dyes using TiO2 has appeared promising in laboratory studies, but little attention has been focused on whether other species such as might be found in wastewater have a deleterious effect on the photobleaching. This study describes the effects that result from the presence of ionic species, organic solvents and humic substances on the photobleaching of several dyes. The manner in which the photobleaching was affected by the presence of adventitious materials was carefully examined with an eye toward elucidating the mechanistic origin of the loss of the photochemical efficiency in the reaction. The overall retardation effects can be attributed to the combination of light attenuation, inhibition and competition effects.

Titanium dioxide was shown to be generally effective as a catalyst for photobleaching many structural classes of organic dyes in aqueous solution, using visible light. However, results from study of 15 dyes indicate that photobleaching rates differ significantly from families of dyes with different functionalities, and are dependent on the light source and crystalline form of TiO2 used. Sorption characteristic on the TiO2 surface and the aqueous solubility of the dyes also play an important role in the photobleaching rate. Kinetic analysis indicates that the dye photobleaching rates can usually be approximated as pseudo-first-order kinetics. In addition to the generally proposed photocatalytic oxidation mechanism for TiO2 reactions, we observed evidence for two kinds of electron transfer mechanisms that are “photosensitized reduction” and “photosensitized oxidation”. Natural sunlight was effectively used to photobleach some of the dyes.

Debromination of 8-bromo-2′-deoxyguanosine was accomplished in high yield under neutral conditions in aqueous methanol by irradiating with visible light in the presence of methylene blue as a sensitizer and triethylamine as an electron donor. The method can be extended for the debromination of other bromoaromatic compounds.

Methods to prevent pollution from toxic heavy metals have been explored through development of nontoxic catalytic alternatives for oxidation of dithianes, oxathianes, and benzyl ethers. Inexpensive spotlights were utilized to induce high-yield preparative scale photoreactions. In this manner, dye-sensitized irradiation of dithianes led to cleavage, generating a dithiol and a carbonyl compound, while oxathiane irradiation led to a carbonyl compound and a hydroxythiol. Trimethoxybenzyl ether irradiation produced an alcohol and an aromatic aldehyde. A single electron transfer mechanism seems responsible for initiating the bond cleavages that mimic electrochemical oxidation of these substrates. An advantage over electrochemistry, however, is that the dye-sensitized transformations are more conveniently scaled up. In this study multi-gram reactions have been performed without difficulty.

Dithio derivatives of aldehydes and ketones have been deprotected under neutral conditions using visible light provided by a 120 Watt spotlight and methylene green as a sensitizer. The key step in the deprotection is apparently an electron transfer from the dithio derivative to the electronically excited visible dye. The resulting dithio radical cation undergoes fragmentation, and the corresponding aldehydes and ketones are isolated in excellent yields.

Irradiation of epoxides in the presence of amines and sodium borohydride leads cleanly to a regioselective opening of the epoxide, giving the lesser substituted alcohol as a product.

Dithianes and dithiolanes were cleaved in excellent yields to aldehydes or ketones in a deprotection procedure using visible light. A neutral solution of a dithio compound in acetonitrile/water was illuminated under nitrogen using an ordinary tungsten spot light. A dye-sensitized photocleavage of the dithio compound led to near-quantitative formation of the deprotected aldehyde or ketone.

Photocatalytic reduction of chloroaromatics to the corresponding aromatic compounds has been accomplished using visible dyes in the presence of amines. An electron transfer mechanism is implicated by the experimental results, with the formation of an aryl chloride radical anion being the key step leading to dechlorination.

Superior yields of N-alkylated nitrogen heterocycles have been achieved with remarkable regioselectivity. The lithium salt of the heterocycle was prepared by treatment with butyllithium in tetrahydrofuran. Reaction of this salt at room temperature with electrophiles, such as alkyl methanesulfonates and 1,2-epoxypropane, bearing an oxygen leaving group proceeded quantitatively and gave exclusive N-alkylation with no detectable C-alkylation.

The Rose Bengal-induced photofragmentation of beta-amino alcohols has been previously reported to proceed through a mechanism involving singlet oxygen sensitization, followed by attack of singlet oxygen and superoxide on the beta-amino alcohol. An alternative mechanism involving electron transfer from the amine to the excited state Rose Bengal is supported by new evidence.

The photochemistry of dibenzo-1,4-dioxin (7) and 2,3,7,8-tetramethyldibenzo-1,4-dioxin (15) — both of which have the parent ring system of the well-known enrimental contaminant dioxin— has been studied in aqueous solution and in selected organic solvents. It is shown that a novel intramolecular photorearrangement is the major mode of reaction for 7 and the exclusive reaction for 15, giving rise to observable (by UV—Vis spectrophotometry) intermediate 2,2′-biphenylquinones. Subsequent reduction by the organic co-solvent gives rise to 2,2′-biphenols as major or exclusive product. Thus, photolysis of these compounds generates oxidizing agents in the biphenylquinones. Photolysis in the presence of added NaBH4 resulted is greatly enhanced yields of biphenols along with more than 90% material balance. These findings have relevance to dioxin photodecomposition, which can be used as a method for its destruction.