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Seven new 2,4,6-triarylpyrimidines were synthesized and their solvatofluorochromism investigated in 12 solvents and in an aqueous micellar solution of reduced Triton X-100. A multiparametric analysis of their emission band showed that the solvent dipolarity and basicity were mainly responsible for their solvatofluorochromism, which arose from an internal charge-transfer from a donor fragment to the pyrimidine acceptor, confirmed by theoretical calculations. In the micellar system, quenching of their fluorescence by addition of derivatives of 2,2,6,6-tetramethylpiperidinoxyl (TEMPO) radical was investigated and the results were consistent with the spectral changes brought about by the micro-heterogeneous system., (© 2018 The American Society of Photobiology.)

Photoinduced electron transfer between N-phenylglycine (NPG) and electronically excited triplets of 7-substituted-3-methyl-quinoxalin-2-ones in acetonitrile generate the respective ion radical pair, where by decarboxylation the phenyl-amino-alkyl radical, PhNHCH2•, is generated. This radical reacts with the 3-methyl-quinoxalin-2-ones ground states, leading to the product 2. Other, unexpected, 7-substituted-1,2,3,3a-tetrahydro-3a-methyl-2-phenylimidazo[1,5-a]quinoxalin-4(5H)-ones, annulation products, 3a-f, were generated; likely by the addition of two PhNHCH2• radicals, to positions 3 and 4 of the quinoxalin-2-ones. The reaction mechanism includes a photoinduced one electron transfer initiation step, propagation steps involving radical intermediates and NPG with radical chain termination steps that lead to the respective products 2a-f and 3a-f and NPG by-products. The proposed mechanism accounts for the strong dependency found for the initial photoconsumption quantum yields on the electron-withdrawing power of the substituent. Therefore, photolysis of common reactants widely used such as NPG and substituted quinoxalin-2-ones may provide a simple synthetic way to the unusual, unreported tetrahydro-imidazoquinoxalinones 3a-f., (© 2013 The American Society of Photobiology.)

Photoreduction of 7H-benzo[e]perimidin-7-one (3-AOIA, A1) and its 2-methyl derivative (2-Me-3-AOIA, A2) by non-H-donating amines (1,4-diazabicyclo[2.2.2]octane [DABCO]; 2,2,6,6-tetramethylpiperidine [TMP]), and a hydrogen-donating amine (triethylamine [TEA]), has been studied in deaerated neat acetonitrile solutions using laser flash photolysis (LFP) and steady-state photolysis. The triplet excited states of A1 and A2 were characterized by a strong absorption band with λmax = 440 nm and lifetimes of 20 and 27 μs respectively. In the presence of tertiary amines, both triplet excited states were quenched with rate constants close to the diffusional limit (kq ranged between 10(9) and 10(10) M(-1) s(-1)). The transient absorption spectra observed after quenching with DABCO and TMP were characterized by maxima located at 460 nm and broad shoulders in the range of 500-600 nm. These transient species are attributed to solvent-separated radical ion pairs and/or to isolated radical anions. In the presence of TEA, these transients undergo proton transfer, leading to the neutral hydrogenated radicals, protonated over the N1- and O-atoms. Transient absorption spectra of these transients were characterized by maxima located at 400 and 520 nm and 430 nm respectively. Additional support for these spectral assignments was provided by pulse radiolysis (PR) experiments in acetonitrile and 2-propanol solutions., (© 2013 The American Society of Photobiology.)

In memoriam of Elsa Abuin (1942-2012), teacher, mentor and friend. This Special Issue presents a collection of review articles and papers dedicated to the memory of Elsa Abuin and most of them presented during the Meeting of the Latin-American photochemists (Encuentro Latino-Americano de Fotoquímica y Fotobiología, ELAFOT) held in October 2012 in Córdoba, Argentina., (© 2013 The American Society of Photobiology.)

Dibenzoylmethane and avobenzone photochemistry involves the formation of transient enol isomers (Z and E). Conjugation of the OH group with the carbonyl group in these transient isomers reduces the OH bond energy. A fast reduction of the pre-fluorescent probe (C343T) was observed after addition to photolysed DBM samples in nonpolar solvents. This can be attributed to a hydrogen transfer reaction from the transient E accumulated. While no quenching for Z by TEMPO was detected in the laser flash photolysis timescale. Theoretical calculations of spin densities distribution of the radical formed from Z and E showed a more delocalized distribution that would indicate a low reactivity towards oxygen. Our results suggest that DBM and avobenzone can effectively behave as photoantioxidants or photoactivated antioxidants under conditions where its enol isomers can be accumulated.