John D. Hepworth

Synthesis and photochromic properties of some fluorine-containing naphthopyrans

A series of novel naphthopyrans containing fluorine substituents has been prepared and their behaviour following irradiation with UV light has been investigated. The colourless naphthopyrans exhibit photochromism through electrocyclic opening of the pyran ring. The spectral properties of the resulting coloured naphthalene-based dienones are discussed.

Synthesis and reactivity of some 4-bromo- 2H-chromenes and 2H-thiochromenes

A facile synthesis of 4-bromo- 2H-chromenes and 2H-thiochromenes and of 1-bromo-3,4-dihydronaphthalene from the corresponding ketones and PBr3 is described. In some instances, significant quantities of the phosphonic acids (3) are isolated. Conversion of the bromo compounds to the lithio derivatives provides access to a wide range of novel 4-substituted 2H-chromenes and 2H-thiochromenes.

Red Colouring Photochromic 6′-Substituted Spiroindolinon Aphth[2,1-b][1,4]Oxazines

Electron donating/withdrawing substituents and electronegative centres have been successfully employed in substantially widening the range of photo-generated colours available in the spiroindolinonaphthoxazine class of photochromic materials.

Solid-state fluorescent photophysics of some 2-substituted benzothiazoles

The solid-state fluorescence properties of a series of benzothiazoles with phenyl, naphthalene, and coumarin moieties substituted at the 2-position have been investigated. The necessity for a 2′-OH substituent for fluorescence has been confirmed and the effects of further substitution in the 2-phenyl ring are reported.

Direct aromatic tert-butylation during the synthesis of thiochroman-4-ones

The synthesis of thiochroman-4-ones from thiophenols and 3-methylbut-2-enoic acid effected by methane sulphonic acid is accompanied by tert-butylation of the aromatic ring. 3-Arylthiobutanoic acids, available using β-butyrolactone, are efficiently cyclised in the same manner.

Synthesis and Photochromic Properties of Methoxy Substituted 2,2-Diaryl-2H-naphtho[1,2-b]pyrans

A series of methoxy-substituted 2,2-di(4-methoxyphenyl)-2H-naphtho[1,2-b]pyrans has been synthesised from 3-alkoxycarbonyl-1-naphthols and 1,1-di(4-methoxyphenyl)prop-2-yn-1-ol. The influence of the methoxy group on the wavelength of maximum absorption and the stability of the ring-opened naphthopyrans is discussed.

Synthesis and spectroscopic properties of some merocyanine dyes

The reaction between some 1,1-diarylprop-2-yn-1-ols 3 and cyclohexane-1,3-diones affords merocyanine dyes 7, the valence tautomers of the tetrahydro-2H-[1]benzopyrans. The spectroscopic properties of these dyes are discussed. The isomeric merocyanine dyes 14 and 15 derived from the reaction of 1,1-bis(4-dimethyl-aminophenyl)prop-2-yn-1-ol and 2-tetralone are dehydrogenated to the photochromic 3H-naphtho[2,1-b]pyran 12. This protocol constitutes a new route to the photochromic naphthopyran unit.

The influence of singlet oxygen in the fading of carbonless copy paper primary dyes on clays

Singlet oxygen was shown to be involved in the mechanism of fading on a clay surface of a series of the triphenylmethane (TPM) dyes used in commercial carbonless copying paper. The dyes adsorbed on clays were found to be singlet oxygen sensitisers and the singlet oxygen produced reacted with the dyes themselves. The rate of fading of a particular dye depended upon the structure of the dyes, fluorans degrading faster than phthalides.

Conjugate additions of lithium dialkynylcuprates [(RCC)2CuLi] to activated chromones. Unexpected formation of the 6H-bis[1]benzopyrano[2,3-b:3′,4′-e]pyridine system

Lithium dialkynylcuprates [(RCC)2CuLi], 1a–d, are easily generated and undergo conjugate additions to activated chromones giving 2-alkynylchroman-4-ones 4a–d, 13, 15c,d and 5, however, 1,4-additions to 3 proceed anomalously to give the eneynonitriles 6a–b and the bisbenzopyranopyridine 7.

An investigation of the electronic spectral properties of the coloured photoproducts derived from some photochromic naphtho[2,1-b]pyrans

Abstract Some chromenes are of current interest as photochromic dyes. The results of PPP molecular orbital calculations, after refinement by parameter optimisation, were found to provide a reasonable account of the experimental λ max values for the ring-opened photoproducts formed from a range of substituted naphtho[2,1- b ]pyrans. The agreement between experimental and calculated values was less good for two compounds, but this may be explained on the basis of steric constraints which are likely to reduce molecular planarity. The electronic structure of one of the photoproducts and the nature of the electronic excitation process are discussed in terms of the calculated π-electron charge densities.