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The dyes Nile Blue (C. I. Basic Blue 12, NB) and Thionine (C. I. 52000, TH) were examined in both ionic and neutral forms in different solvents using NMR and UV-visible Spectroscopy to firmly establish the structures of the molecules and to assess the nature and extent of their aggregating characteristics. 1H and 13C NMR assignments and chemical shift data were used along with (for NB) nuclear Overhauser effect information enabling a structure for self-assembly to be proposed. In both cases these data were supplemented with variable temperature, dilution and diffusion-based experimental results using 1H NMR spectroscopy thereby enabling the extended aggregate structures to be assessed in terms of the relative strength of self-association and the extent to which extended aggregates could form. Full and detailed solution phase NMR analysis of such dyes, especially the two studied in this context, have either not been widely reported or have not been studied to the depth presented here. The data and their interpretation form an important addition to the analysis of this class of dye compounds and provide additional insight into the effects of self-assembly on the behaviour of such molecules in various solution-phase environments.

A detailed study of the action of alkali on methylene blue (C.I. Basic Blue 9) and other thiazine dyes was carried out through a combination of UV/visible spectroscopy, thin layer chromatography, mass and NMR spectrometry and computational methods. In 0.1 M aq alkali solution, methylene blue forms a highly coloured, lipophilic species that is mainly Bernthsen's methylene violet i.e. a hydrolysis decomposition product, this being contrary to the report of a red N-hydroxy methylene blue adduct. The nature of the heterocyclic nitrogen atom in C.I. Basic Blue 9 is discussed and it is concluded there is no basis for the proposal of nucleophile addition at this site of the dye. In contrast, other thiazine dyes are deprotonated by alkali to form their neutral, highly coloured, lipophilic conjugate base forms.

Pre-formed transition metal-NHC complex is shown to be an effective catalyst for Atom Transfer Radical Cyclisation (ATRC) reactions. © 2007 Elsevier Ltd. All rights reserved.

A sulfonated o-acetylamino arylazo compound unexpectedly cyclised to a cationic benzo-1,2,4-triazinium species under thermal or acid conditions, reversible with base. The same substrate underwent trans to cis-azo photoisomerisation, observable by NMR spectroscopy, under steady state laser irradiation conditions.

Pronounced solvatochromic shifts are observed in the visible spectra of two series of heteroarylazobenzene derivatives based on m-acetylamino- and m-methyl-N,N-diethylaniline, measured in various solvents. The heteroaryl azo component of these dyes can be viewed as a thiophene ring substituted by cyano, nitro, alkoxycarbonyl, or ring aza (to give thiazole and isothiazole derivatives). Free-Wilson analysis has shown that the influence of each of the substituents is constant across all molecules within the two series for a given solvent. However, the substituent increments vary between different solvents and correlate with the Kamlet-Taft dipolarity/polarisability parameter pi* of the solvents. There appears to be no intuitive explanation for the relative solvent variation of different substituents, but Onsager theory suggests sensitivity to the relative size and shape of the dyes. Visible absorption maxima are predicted for unknown heteroarylazo compounds related to those studied.

Addition of cyanuric chloride 2 (2,4,6-trichlorotriazine) to 4,6-diaminobenzene-1,3-disulfonic acid 1 gives a bis-triazine 3 which may be cyclised with diaminoarenes to yield water-soluble azacalix[4]arenes 5a–d. Alternatively, double substitution of chloride from the bis-triazine 3 yields new bis-triazine derivatives which may likewise be cyclised to functionalised azacalixarenes bearing functionalised side chains.

The paramagnetic complexes [Mo(NO)(Tp ∗ )Cl(NC 5 H 4 -4-{CHCHC 6 H 4 -4OC n H 2 n 2)})] {Tp ∗ = HB(#,5-Me 2 C 3 HN 2 ) 3 ; n = 6, 8, 12} have been synthesized and characterized by spectroscopic methods. Polarizing hot stage microscopy studies provided no evidence of mesogenic phases.

PISYSTEM for Windows is a commercial program based on a modified PPP SCF-CI-MO model for the rapid and convenient calculation of excited state properties, especially colour, of π-conjugated systems such as dyes. The use and performance of the program is reviewed.

The title reaction leads to a stable add-ester, an isocoumarin and the two isomeric 3-methoxy-4-methoxycarbonyldihydroisocoumarins. X-ray structure determination of one of these isomers reveals a trans-diaxial conformation. N.m.r. data indicate this geometry also pertains in solution. 1H-13C vicinal coupling constants for the alternative cis-isomer correspond to equatorial-3-methoxy, axial-4-methoxycarbonyl. The trends of two 13C n.m.r. chemical shifts are opposite to those suggested by literature precedents. Empirical force field calculations are consistent with the experimentally determined conformations.

A combination of 4-nitro and 5-N-pyridinium groups in a donor-substituted azobenzene leads to an unexpected bathochromic shift in visible absorption maximum compared with the 5-chloro precursor, despite increased steric interaction between the two substituents. This behaviour probably derives from an intramolecular polarisation effect of the cationic pyridinium group acting on the adjacent nitro group. Molecular orbital calculations support this conclusion. The visible spectra differences in various solvents can be related to solvent dipolarity as reflected by the Kamlet-Taft π * solvent parameter. There is no relationship with H-bonding parameters.

An oligomeric material has been synthesised which consists of three chromophores attached to a polar diamide backbone, each chromophore being derivatised with a hydrocarbon chain to provide hydrophobic character. The molecule forms stable Langmuir films over a pure water subphase with a surface pressure-area per molecule isotherm which rises to 50 mN m −1 before collapse. The area per molecule obtained by extrapolating to zero pressure can be modelled by a structure adopting a double-S configuration of the backbone at the water surface. This can be achieved by the amide linkages adopting the cis rather than trans configuration at the air-water interface and in the Langmuir-Blodgett (LB) film. LB films are readily deposited onto glass. A neutron scattering study of the LB multilayer has given a detailed description of the structure adopted in the LB film.

The phosphonate ester group, typified by P(O)(OPh)2, is an effective π-electron acceptor group in donor-acceptor substituted benzenoid compounds for nonlinear optics, and has the added attractions of being easily functionalised for further fabrication into cross-linked films, and imparting transparency to simple derivatives.

The residual electronegativity of an atom in a molecule can be used as a quantitative measure of the polar infuence of a substituent on reactivity, as exemplified by its ability, with substituent polarisability, to correlate the proton affinity data of 80 amines.

Two simple new models of substituent polarisability have been devised to take into account attenuation of substituent influence, and have been used to quantify electron relaxation effects in core-ionised chlorine and nitrogen compounds, and relative stabilisation of protonated alkylamines.

Ring-opening of methoxymethylidene-substituted homophthalic anhydride (1) by methoxide occurs by two modes. Attack at the 1-position (“benzoate” carbonyl) leads to a stable acid-ester. A combination of unambiguous syntheses and 1H- and 13C-n.m.r. spectroscopy has been used to show that this material has the “benzoate ester, acrylic acid” structure (5). This corrects the structure assignment given earlier for this material, which incorrectly concluded “benzoic acid, acrylate ester”, (2). Compound (2), resulting from attack at the “acrylate” carbonyl, is a co-product of (5), but is unstable. It recyclises in an alternative fashion to give (dihydro)isocoumarin-type products (15) and (16).

Cyclisation of 2-arylazophenylacetic acid with oxalyl chloride gives novel 2-aryl-3-cinnolinones in good yield. Mixed ketene acetals derived from the corresponding phenylacetate esters also give the same product, sometimes with 2-arylindazoles, on treatment with titanium tetrachloride.

Visible absorption spectra have been recorded for azo compounds derived from 2,5-dichlorosulphanilic acid azo-coupled with N , N -diethyl-m-phenylenediamine, and with azine analogues. The effects of the ring-aza substituents as well as cyano on the spectra indicate a surprising difference in sensitivity of the two ring positions meta to the azo group. M.O. calculations show chat the amino group ortho to the azo linkage introduces asymmetry into the HOMO, and this is responsible for the differing effects of substitution.

A mathematical model is defined to represent tetraarylmethanes. The skeletal permutations of this model are described and analyzed in terms of mode equivalent rearrangements. This analysis is applied to an interpretation of the previously published results of a DNMR study of tetra-o-tolylsilane and analogs. A mechanism for the rearrangement is then postulated. The group of permutational flips is described and combined with the skeletal group to give the full permutation group of tetraarylmethanes.

N -aryl derivatives of 4- p-dimethylamino pyridine are novel examples of donor-acceptor dyes. Para -substituents in the N -aryl group influence the spectra, such that the more electron-withdrawing lead to more bathochromic shifts. However, a 2-nitro substituent in the N -aryl ring has surprisingly little influence on the absorption maximum. PPP-MO-CI calculations, and correlation and conformational analyses are applied to the study.

Para- and meta-N-pyridinium-substituted anilines have been synthesised by displacement of dinitroaniline from N-(2,4-dinitrophenyl)pyridinium chloride by p-phenylenediamine or m-acetylaminoaniline in hot DMF. Diazotisation and coupling with N,N-diethylaniline gave azo compounds, with visible absorption maxima: p-pyridinium isomer, 486 nm (neutral), and 504 nm (acid); m-pyridinium isomer, 456 nm (neutral), and 508 nm (acid). Dual-parameter relationships have been derived for a series of substituted azo compounds, connecting their halochromic shifts (difference in visible absorption maximum between neutral and protonated forms) and the electronic substituent constants, σ 1 and σ R . Via these relationships, values of σ 1 = 1.01 and σ R = 0.05 have been derived for the N-pyridinium substituent. Thus, this group is shown to be an exceedingly powerful electron-withdrawer, exerting its effect mainly by inductive/field effects. Its effect on the colour of azo dyes is roughly equivalent to that of the nitro group.