Reuben B. Girling

Effect of metal cations on the photochromic properties of spironaphthoxazines conjugated with aza-15(18)-crown-5(6) ethers

Spironaphthoxazines conjugated with aza-15(18)-crown-5(6)-ether moieties at the 6′-position of the naphthalene fragment (Crown-containing Spironaphthoxazines, CSN) were synthesised and studied for the first time. The addition of Li+ and alkaline earth (Mg2+, Ca2+, Sr2+ and Ba2+) metal cations to CSN solutions results in a hypsochromic shift of the UV absorption band of the spiro form and a bathochromic shift of the absorption band of the merocyanine form in the visible region. In addition, the equilibrium shifts to the merocyanine form, and the lifetime of the photoinduced merocyanine form increases. Analysis of the spectral and kinetic data allows a complexation scheme to be proposed and the stability constants of the resulting complexes to be calculated. According to the results obtained, the complexation with Li+ and alkaline earth metal cations in acetonitrile initially involves the crown ether moiety; the participation of the merocyanine oxygen atom in the complexation process occurs at a high metal cation concentration. The UV-induced isomerisation of CSN into the merocyanine form causes a decrease of the cation binding ability.

Free radical studies by resonance Raman spectroscopy. Part 3.—4-Nitrobenzoate radical Dianion

The free radical di-anion of 4-nitrobenzoate has been produced in aqueous solution by reduction of the parent compound with dithionite. Under steady-state continuous flow conditions the resonance Raman spectrum of the radical could be observed. This spectrum has been interpreted through normal coordinate analysis and molecular orbital calculations, comparisons with the spectrum of the parent being used to determine changes in the force field arising from the different electronic distributions in parent and radical.

Raman characterization of charge-transfer transitions in ligand-bridged binuclear polypyridyl complexes of ruthenium(II)

In the ligand-bridged complexes [(bipy)2Ru(dpp)Ru(biq)2]4+ and [(biq)2Ru(dpp)Ru(biq)2]4+[dpp = 2,3-bis(2′-pyridyl)pyrazine, bipy = 2,2′-bipyridine and biq = 2,2′-biquinoline], the photophysical and redox properties do not allow differentiation of the low-energy charge-transfer transitions Ru → biq and Ru → dpp. Based on the selective resonance enhancement of the intensities of the Raman bands of the ligand biq by excitation within the lowest-energy absorption band, the lowest excited states in the dinuclear complexes have been assigned unambiguously to Ru → biq charge transfer.

Free radical studies by resonance Raman spectroscopy. Part 2.—Diazabicyclo-octane radical cation

The short-lived free radical cation of diazabicyclooctane has been studied in aqueous solution by resonance Raman spectroscopy. The radical was produced at ∼10–4 mol dm–3 concentration by chemical oxidation of the parent compound in a continous flow apparatus. The spectra of both parent and radical have been interpreted in detail through normal coordinate and molecular orbital calculations. These indicate that weaking of the C—C bonds results from electron removal, with a lesser increase in the C—N bond strengths. Evidence for strong solvent effects is presented.

Analytical Potential of Raman Spectroscopy in Wool Textile Research

dycings arc given in Table I. The dycs had moderate lightfastness ratings (about 5 on European system) on polyester. The introduction of different electron donating substitucnt groups in the anthraquinonc chromophore modified the color of the resulting dyes, but this had a minimal effect on the lightfastness of the dyes, except on triacetate where the lightfastness was good (dycs la, b, d, c, g, k, I). Sublimation fastness on polyester fibers was generally moderate (Table I). The initial mark-off of the dyes improved compared with the standard dye IS (35OC difference). Comparing the results of dye IS and dye Ic, f, i, and e, it follows that thc latter with a large molecular size gave a highel initial mark-off temperature. This is in agreement with earlier work done by Fourncss [2]. In the case of the 1,4-bis-(8-hydroxy ethyl) anilino compound, the presence of two polar groups may also contribute to the increased initial mark-off temperature. The presence of a methoxy group in the 2-position has no appreciable influence on the results. The improved initial mark-off temperature is mainly due to the increased molecular weight; In conclusion, substituted aryl derivatives of 1,4diamino-2-methoxy anthraquinonc on polyester fibers were excellent in the range of deep reddish violet, blue, and green. These dyes had moderate lightfastness on trice1 and pol yestcr fibers. I -4-bis-(8-hydroxy cthyl) anilino compound gave fairly good lightfastness on cellulose acetate and triacetate fibers. Sublimation fastness of these dycs on polyester fiber improved when compared with the standard dye. These dyes may be successfully applied by heat transfer printing to polyester, where only a temperature of 160-220°C is necessa ry.

Free radical studies by resonance Raman spectroscopy. Part 1. The 1,4-dimethoxybenzene radical cation

The short-lived 1,4-dimethoxybenzene radical cation has been generated in acidic aqueous solution by oxidation of the parent molecule with cerium(IV). By performing the reaction under fast flow conditions the free radical has been studied in a steady-state condition by resonance Raman spectroscopy. Molecular orbital and normal co-ordinate calculations have been employed in analysing the resulting spectra in terms of the changes in structure and bonding which accompany radical formation in this system.

Resonance Raman spectrum of the p-phenylenediamine radical cation

The Raman spectrum of the free radical formed by oxidation of p-phenylenediamine in solution has been obtained by the method of resonance enhancement; this radical spectrum is shown to differ substantially from that of the parent compound and some preliminary assignments are reported.