On the triplet state of poly(N-vinylcarbazole)

Triplet state properties including transient triplet absorption spectrum, intersystem crossing yields in solution at room temperature and phosphorescence spectra, quantum yields and lifetimes at low temperature as well as singlet oxygen yields were obtained for poly(N-vinylcarbazole) (PVK) in 2-methyl-tetrahydrofuran (2-MeTHF), cyclohexane or benzene. The results allow the determination of the energy value for the lowest lying triplet state and also show that triplet formation and deactivation is a minor route for relaxation of the lowest excited singlet state of PVK. In addition, they show the triplet state is at higher energy than reported heavy metal dopants used for electrophosphorescent devices, such that if this is used as a host it will not quench their luminescence.     

Thiophene–phenylene/naphthalene‐based step‐ladder copolymers

A series of step‐ladder copolymers based on thiophene–phenylene–thiophene SL1 ‐ SL3 and thiophene–naphthylene–thiophene SL4 repeat units with varying lengths of the oligothiophene segment has been designed and synthesized via a microwave‐assisted Stille‐type cross‐coupling reaction followed by a polymer‐analogous cyclization reaction. The optical properties of the step‐ladder copolymers have been investigated in detail, in particular at low temperature and in the solid‐state. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7342–7353, 2008     

Environmental and laboratory studies of the photodegradation of the pesticide fenarimol

The photophysics and photochemistry of the pesticide fenarimol were studied. From the absorption and fluorescence spectra, quantum yields and lifetimes, it is suggested that the lowest excited singlet state has predominatly n,π^* character, and is localized on the pyrimidine ring. Phosphorescence measurements suggest a small singlet—triplet splitting. Halide ions are found to quench fenarimol flourescence. Photodecomposition of fenarimol in a variety of solvents was studied by gas chromatography—mass spectrometry. Although the products have not yet been characterized, degradation of this compound appears to involve cleavage of bonds to the quaternary carbon without significant dechlorination. Preliminary studies of the kinetics and relative quantum yields of photodegration show that the reaction proceeds via a first-order process, which is independent of pH, but which involves a photoactive intermediate. Chloride and bromide ions inhibit the photolysis,whereas the triplet quencher sorbic acid has no effect.     

Solution behaviour of lead(II) carboxylates in organic solvents

The solution behaviour has been studied of a series of even chain length lead(II) carboxylates (octanoate to octadecanoate) and the odd chain length lead(II) heptadecanoate in a variety of non-complexing organic solvents and in alcohols. In agreement with previous studies, solubility increases dramatically above a certain temperature, which depends on solute concentration, chain length and solvent. This solution temperature is also affected by traces of water. These results are complemented by studies using vapour pressure osmometry, dynamic light scattering, ¹H and ¹³NMR spectroscopy. The results in water-free systems are consistent with the formation of rather ill-defined, polydisperse aggregates, which increase in size with concentration and decrease with temperature. These show similar local structure to lamellar mesophases in the pure lead(II) carboxylates, and are suggested to be formed by solvent induced swelling and break-up of these mesophases. In the presence of water, a more ordered structure is formed, in which a few water molecules are suggested to be bound to the lead(II) carboxylate headgroup.     

Electrophysiological evidence for the critical band in humans: middle-latency responses

Electrophysiological evidence for the critical band phenomenon in humans using event-related potentials has been sought for many years with conflicting results. Components Na and Pa of the middle-latency response (MLR) and wave V of the auditory brain-stem response (ABR) were simultaneously recorded in response to a two-tone complex varying in bandwidth from 76 Hz to 1012 Hz, centered at 2 kHz, and presented at an overall level of 85 dB SPL, in ten normal female subjects. Only the amplitude of Na showed an abrupt increase as bandwidth changed from 268 to 330 Hz, yielding an estimate of critical bandwidth in good agreement with previous behavioral estimates.     

Room temperature rate coefficient for the reaction between CH3O2 and NO3

The molecular modulation spectroscopic technique was employed to study the kinetics of NO₃ radicals produced in the 253.7 nm photolysis of flowing gas mixtures of HNO₃/CH₄/O₂ at room temperature. By computer fitting of the NO₃ temporal behavior, a rate coefficient of (2.3 ± 0.7) × 10^?12 cm³ molecule^?1 s^?1 was obtained for the reaction between NO₃ and CH₃O₂ at 298 K.