The interactions between triplet state benzophenone and halide anion species (Cl , Br and I have been studied by laser flash photolysis (at 355 nm) in aqueous solutions at room temperature. The decay of the triplet state of benzophenone was followed at 525 nm. Triplet lifetime measurements gave rate constants, k q (M −1 s ), close to diffusion controlled limit for iodide (~8×10 9 M −1 s ), somewhat less for bromide (~3×10 8 M −1 s ) and much lower for chloride ( 6 M −1 s ). The halide (X − ) quenches the triplet state; the resulting product has a transient absorption at 355 nm and a lifetime much longer than that of the benzophenone triplet state, is formed. This transient absorption feature matches those of the corresponding radical anion (X 2 ). We therefore suggest that such reactive quenching is a photosensitized source of halogen in the atmosphere or the driving force for the chemical oxidation of the oceanic surface micro layer.

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Photoinduced oxidation of sea salt halides by aromatic ketones: a source of halogenated radicals

Anthracene (III) and the derivatives 9-methoxymethylanthracene (IV), 9-cyanoanthracene (V) and (E-3-phenyl-prop-2-ene-1-yl(anthracene-9-methyl)-ether) (I) were subjected to irradiation at inca347 nm in dilute deoxygenated acetonitrile solution at room temperature. With the aid of the flash photolysis method employing fluorescence, optical absorption and electrical conductivity measurements the monophotonic photoionization and the formation of free ions was evidenced for compounds III‐V. In the case of the bichromophoric compound I a photocurrent was not observed although a transient optical absorption attributable to the radical anion of the arthracene moiety was detected. Moreover, the fluorescence lifetime of I was found to be definitely shorter than that of IV (model compound). On this basis it was concluded that a certain fraction of electronically excited singlet states of I is deactivated via intramolecular electron transfer. The transient zwitter ions formed in this way, overwhelmingly undergo a self-reaction thus regenerating I, but a small portion undergoes an intramolecular Diels‐Alder reaction forming VI, the only photoproduct. The quantum yield is (VI)0.04. # 1999 Elsevier Science S.A. All rights reserved.

Photoionization of anthracene and anthracene derivatives

The synthesis is described of a photoactive molecular dyad comprising a luminescent ruthenium(II) tris(2,2‘-bipyridyl) fragment covalently attached, via a methylene bridge, to a calix[4]arene recep...

Conformational control of intramolecular electron transfer in calix[4]diquinones and their cationic complexes

Reported herein is the high yielding synthesis of a new fluorenone-based triazolophane and its sensing capabilities for polycyclic aromatic hydrocarbons (PAHs) and fluoride anions Fluorescence, UV/Vis and 1H NMR spectroscopy results showed the triazolophane has a high sensitivity for selected PAHs and binds the fluoride anion in a 2 : 1 stoichiometry via C–H hydrogen bonding with the triazole and fluorenone protons

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A highly versatile fluorenone-based macrocycle for the sensitive detection of polycyclic aromatic hydrocarbons and fluoride anions

Substituent effects on the bond-cleavage mode in the singlet excited state as well as on the initiation ability for photopolymerization were investigated on the title anthracenemethanol derivatives ( 1 ). Analysis of substituent effects on the excited-state reactivity and product distribution revealed that intramolecular electron transfer in 1 having the aroyl group is responsible for its excited-state deactivation while the heterolytic and selective CH 2 O bond cleavage is induced on forming a singlet exciplex with some charge-transfer character. It was suggested that substituted benzoate ion-bridged anthrylmethylcarbonium ion is a key intermediate in the photodecomposition process of aroyl-substituted derivatives. On the other hand, less electron-withdrawing acetyl-substituted derivative undergoes the heterolytic CH 2 O bond and homolytic CH 2 O C( O) bond cleavages to form geminate anthrylmethyl carbonium-acetate ion pair and anthrylmethyloxyl-acetyl radical pair, respectively. An examination of the ability of 1 to initiate radical and cationic photopolymerizations allowed us to propose that O -anisoyl anthracene-9-methanol is a likely candidate for novel hybrid-type photoinitiator.

Bond-cleavage mode of O-acyl anthracene-9-methanol derivatives in the singlet excited state and their abilities to initiate radical and cationic photopolymerizations

The solvent and temperature dependence of the excited state properties of anthracenes non-conjugatively linked to various aromatic phenones have been investigated by determination of the quantum yields of fluorescence and intersystem crossing. In a series of substituted bichromophoric ω-(9-anthryl)propiophenones, the degree of intramolecular quenching of the anthracene fluorescence by the phenones was not compensated for by increasing intersystem-crossing efficiency in the anthracene chromophore, but was found to be associated with the standard free-energy change for intramolecular charge separation, the solvent polarity and the temperature. In contrast, in monochromophoric anthracene reference compounds neither remarkable solvent polarity nor temperature dependence of the fluorescence emission was detected. For example, for one bichromophoric compound [ω-(9-anthryl)-4′-methoxypropiophenone] an analysis within the framework of the Marcus electron-transfer theory was performed and a dependence of the nuclear Franck–Condon factor for the intramolecular charge-separation reaction on the solvent polarity was found. Shortening the linking non-conjugative bridge in one bichromophore [ω-(9-anthryl)propiophenone] resulted in an increased charge-separation rate constant by more than one order of magnitude in ω-(9-anthryl)acetophenone.

Intramolecular deactivation of photoexcited anthracenes by aromatic ketones. Part 2.—Charge-transfer deactivation of ω-(9-anthryl)ketones in different solvents and binary solvent mixtures and at different temperatures

The excited state properties of anthracenes non-conjugatively linked to various types of aromatic ketone were investigated in non-polar solution by determination of the quantum yields of fluorescence and intersystem crossing. In a series of substituted bichromophoric ω-(9-anthryl)propiophenones, the degree of intramolecular fluorescence quenching by the ketone was found to be associated with an increase in the quantum yield of anthracene triplet state formation. Excitation of 4′-piperazinoacetophenone tethered to anthracene resulted in deactivation within the acetophenone chromophore, rather than singlet energy transfer to anthracene. For photoexcited anthracene linked to 2-amido-substituted fluorenone, intramolecular exothermic transfer of the singlet excitation energy to the fluorenone chromophore was found to proceed with high efficiency.

Carsten Burgdorff

Papers

Intramolecular deactivation of photoexcited anthracenes by aromatic ketones. Part 2.—Charge-transfer deactivation of ω-(9-anthryl)ketones in different solvents and binary solvent mixtures and at different temperatures

Intramolecular deactivation of photoexcited anthracenes by aromatic ketones