Journal of Photochemistry最新文献

The association of the excited state derived from four imidazo[4,5-f]-quinolines with 2-propanol in cyclohexane has been studied. The unusual bathochromic shift and bandwidth of the fluorescence spectra of these heterocyclic compounds in 2-propanol—cyclohexane solutions compared with those obtained in cyclohexane solutions have been attributed to the association of the excited state imidazoquinolines with the 2-propanol molecules. Hydrogen bonding between the imidazole

The reactions of the cis- and trans-2-butenes photosensitized by Zn(³P₁) have been studied. The main reaction was cis—trans isomerization. The photostationary [trans]/[cis] ratio was 1.5/1.0 and did not vary with pressure. This ratio is different from those obtained in the mercury- and cadmium-photosensitized reactions. The isomerization of 2-butenes photosensitized by Zn(³P₁) could not be explained in terms of the simple mechanism proposed for the mercury- and cadmium-photosensitized reaction of 2-butenes. Possible mechanisms are discussed.

An argon laser beam was used to perturb the NO₂-N₂O₄ chemical system. The perturbation was monitored, in different experiments, with the laser-induced fluorescence and the IR optical double-resonance (IODR) techniques. The expected quantum perturbations which involve specific rotational levels in NO₂, $\text{X}$ ²A₁ were observed. Unexpected chemical effects which involve the ground state concentration of both species and which are attributed to the response of the chemical equilibrium to the optical perturbation were also observed. The IODR results are discussed with the help of a model based on the Beer-Lambert law, which allows the role of the chemical response to be demonstrated.

The addition of aluminium compounds to 1,4-dihydroxyanthraquinone (quinizarin (QH₂)) in either aqueous or non-aqueous solutions results in the formation of a highly fluorescent pink-red complex with excitation maxima at 500, 530 and 573 nm and corresponding emission maxima at 585 and 619 nm. Analysis by absorption spectroscopy using mole ratio and continuous variation techniques indicates the formation of 1:1 and 2:1 Al:QH₂ complexes. Fluorescence quantum yields in excess of 0.8 have been measured in n-butanol. Observations on the stability and the spectroscopic properties of the 2:1 complex are presented, together with a plausible structure.

An improved analytical procedure, which uses a fast Fourier transform (FFT) algorithm, has been developed to deconvolute luminescence decay curves. Using this procedure, the non-exponential fluorescence decay curves recorded from the excited singlet state of magnesium tetraphenylporphyrin in the presence of CBr₄ in frozen solution, in which both radiative transfer and electron transfer quench the excited state, have been examined. This procedure eliminates the common “overlap effect” that is inherent in previous uses of FFT methods when applied to the problem of deconvoluting decay curves, through a systematic reconstruction of the input data. The analysis may be performed either in the time domain or in the frequency domain. An interactive program, DECAYFIT, written in Fortran 77 was used to carry out the calculations on the IBM S9001 laboratory microcomputer. The program can be employed to deconvolute both model test data and real data, with a time for the analysis in the range of minutes.

The pulse d.c. photoconductivity (PC) of the vacuum-degassed ethers tetrahydrofuran (THF), ethyl ether (Et₂O) and 1,4-dioxane was investigated. It was found that after a light pulse of duration 1 ms in degassed THF or Et₂O the photocurrent rises. A monophotonic ionic photodissociation is responsible for the charge generation since the photosignals were proportional to the amount of absorbed light. The photocurrent signals decreased exponentially with first-order rate constants which decreased linearly with the decreasing voltage applied between the platinum electrodes. This might indicate that the fairly stable photoproduced ions disappear mainly in the electrode discharge reactions. The bulk recombination, which is probably preceded by a monomolecular or pseudomonomolecular rearrangement (since this is a process also well described by an exponential equation) did not exceed about 10% of the total ion consumption under the conditions used. After examining different methods of purification of the ethers studied it was found that the phenomenon was caused by electron acceptor impurities, which were mainly the products of the oxidation of ethers. In the case of 1,4-dioxane the PC signals were hardly detectable, since the lower polarity of this solvent did not favour ionic dissociation of the ion pairs which are probably also produced. An improved method of purification of these ethers is proposed.