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The purpose of this work is to suggest a way to utilize image statistics to guide optimization of brightness distributions, towards a goal of complete systematization of image processing to achieve a purely aesthetic objective, with entropy as a response metric. We start with a survey of classic pictorial photographs, proceed to a heuristic theoretical treatment of the brightness distribution function, and follow with several pictorial illustrations of the proposed concept.

We have compared the photooxidation of the title compound, DEA, by diphenyliodonium salts in homogeneous acetonitrile (AN) and in heptane/AOT/water reverse micelle solutions. The reaction is efficient, which we attribute to rapid (ca. 10 ps) deethylation of the DEA radical cation, initially formed by photoinduced electron transfer. In AN, the electron transfer occurs from singlet excited DEA, but in reverse micelles it is gated by intersystem crossing to triplet DEA. Under these conditions, DEA fluorescence quenching by the iodonium cation may still be observed; we infer operation of the external heavy atom effect as the primary mechanism. Keywords: anthracene, electron transfer, reverse micelle, photochemistry, picosecond.

Photoexcitation of the title compound (DMBA) in polar solvents leads to sequential formation of at least three excited species as detected by laser transient absorption spectroscopy: the lowest Franck–Condon singlet, a twisted singlet (P-state), and the lowest triplet states. Only the initially formed, localized singlet is emissive under our conditions. Interystem crossing to triplet occurs primarily from the twisted P-state in acetonitrile and in methanol. Photo-CIDNP and quantum yield measurements indicate that electron transfer occurs exclusively from the triplet in acetonitrile or methanol to sensitize decomposition of diphenyliodonium cation and to bleach DMBA. Analysis of the photochemistry is complicated by formation of a charge transfer complex of enhanced photolability. Using tris(trichloromethyl)-sym-triazine as the electron acceptor in hydrocarbon solvent, bleaching of DMBA again occurs, somewhat more efficiently than with the 'onium salt in polar solvent. We infer that under these conditions electron transfer occurs from the P-state. Keywords: photochemistry, fluorescence, electron transfer, TICT, chalcone.

Previous studies on photooxidation of 9,10-diethoxyanthracene (DEA) with diphenyliodonium cation revealed dealkylation of DEA radical cation. Fluorescence, dealkylation quantum yield, and laser-flash transient absorption spectroscopic studies on DEA and its dimethoxy (DMA) and diisopropoxy (DIPA) analogs, probed solvent and substituent effects on this reaction. We reconsider our original inferences as to relative rates of dealkylation and back electron transfer; the results pose new questions, e.g., as to the role of orbital symmetry in controlling rate of back electron transfer.

Pulsed picosecond laser photolysis of the diphenyliodonium cation indicates that excitation of the allowed transition is followed by rapid (ps) deactivation to a homolytically dissociative state, presumably T1. Steady-state photolysis yields iodobenzene and biphenyl from the primary radical products. Iodobiphenyl is also observed. We infer in-cage recombination of these radical products, with intervention of a carbocationic intermediate. Laser flash photolysis of diphenyliodonium iodide in its charge transfer band yields an initial transient with a lifetime of ca. 200 ps. A strongly absorbing secondary transient is observed on the nanosecond time scale. Iodobenzene is the exclusive reaction product. We infer that it is not formed directly from the primary photoproduct, but through in-cage recombination of phenyl cation with iodide anion, as in benzenediazonium iodide.

We have studied the anthracene-sensitized photolyses of both diphenyliodonium and triphenylsulphonium salts in solution using both steady-state and laser flash photolysis techniques. Photoproducts, namely, phenylated anthracenes along with iodobenzene or diphenylsulphide, respectively, are obtained from both salts with quantum efficiencies of ca. 0.1 at 375 nm. We infer the intermediacy of diphenyliodo and triphenylsulphur radicals formed by single electron transfer from the singlet-excited anthracene. We have developed a quantitative model of this chemistry, and identify the principal sources of inefficiency as back electron transfer, which occurs at nearly the theoretically limiting rate, intersystem crossing from the initially formed sensitizer–'onium salt encounter complex, and in-cage radical recombination.

Fluorescence quantum yields and emission lifetimes have been measured at room temperature for a series of thiacarbocyanine dyes in various alcohol solvents. All radiationless deactivation events are accounted for by a process, e.g., torsional relaxation, whose rate is viscosity-dependent. The relaxation rate constant (kη) and the exponent of viscosity dependence (α) in the Wirtz−Gierer analysis decrease with increasing polymethine chain length (n) in the dye series. Two dyes were further examined by time-resolved picosecond laser flash spectroscopy. Recovery of ground state in both cases is biphasic. In both cases, the short recovery time corresponds to the fluorescence lifetime. We infer that torsional relaxation of the vertical S1 state is rate determining and does not cross between the S1 and So potential surfaces in the relaxed S1 conformation. The slower recovery process is identified with a pathway that leads to photoisomerization of the cyanine chromophores and implies involvement of a species intermediate between torsionally relaxed S1 and the ground-state photoisomer. This intermediate is suggested to be an isomerized triplet state.

The photocatalytic deposition of silver from ethanol solution on TiO2 nanoparticles prepared with a chemisorbed surface alkoxide layer has been examined in real time by picosecond-resolved transient absorption spectroscopy. This photocatalyst formation of surface-trapped photoelectron states, hypothesized to be Ti(III), can be followed on the time scale of the experiment (≤10 ns). Loss of these electrons to recombination is inconsequential, presumably owing to sacrificial hole trapping by the surface alkoxide states. Silver deposition occurs on the same time scale, and the pseudo-first-order rate constant for growth of the silver(0) transient absorption is the same as for the disappearance of the Ti(III) states under these conditions. We infer that one-electron, inner sphere reduction of Ag(I) by Ti(III) is rate determining in the formation of the colloidal silver deposit. These particles must accordingly grow by a sequence of alternating electronic and ionic events analogous to those hypothesized to be involved in latent image formation in silver halide photography. The quantum yield for silver deposition under our conditions was estimated as ca. 0.8, much higher than that reported by other authors (refs 1, 2, and 6).

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THE binding of non-ionic aromatic compounds to bovine serum albumin (BSA) has been approached in terms of the equilibrium between the bound and crystalline states1. The binding is quantitated in terms of the number of molecules of an aromatic compound solubilized per molecule BSA, in aqueous solution in equilibrium with the compound in its crystalline state. The measurement of this number, K, may be visualized as tantamount to the determination of the solubility of the compound in a two-dimensional solution on the surface of the protein molecule. This approach is derived from the interpretation of adsorption phenomena as thermodynamically analogous to solution phenomena2.

Reaction of solid (I) with D2 gas produces cyclooctane containing up to 16 deuterium atoms.