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A study of the ring-contraction of a model 3H-naphtho[2,1-b]pyran is described to elucidate and optimize the ring-contraction of naphthopyrans. Two efficient base-mediated protocols to access multi...

Diversely substituted 1,2-oxathiine 2,2-dioxides, including 3,5,6-triaryl-, 3,6-diaryl-, 3,5-diaryl-, 5,6-diaryl- and selected fused heterocyclic analogues, have been efficiently obtained by the application of a mild Cope elimination of a 4-amino moiety from the requisite 4-amino-3,4-dihydro-1,2-oxathiine 2,2-dioxides, which themselves were readily obtained by the addition of sulfenes to enaminoketones.

A series of ketohydrazone dyes has been synthesised from 4-morpholino-2-naphthol and ortho-substituted anilines by conventional diazotisation coupling chemistry. Whilst the new, dull orange-red, dyes exhibit only a minor variation of absorption maxima across the range of substituents, they are hyperchromic relative to Sudan 1 and their none ortho-substituted analogue. Protonation of selected dye examples results in a bathochromic and hyperchromic shift in absorption maxima to afford vibrant purple-coloured protonated species.

1,2-Oxathiine 2,2-dioxides have been obtained from their respective 3,4-dihydro-4-dimethylamino precursors, for the first time, by a mild Cope elimination of the 4-dimethylamino function. The application of the 1,2-oxathiine 2,2-dioxide scaffold in materials chemistry is exemplified by the efficient P-type photochromism of the 5,6-bis(2,5-dimethyl-3-thienyl) substituted oxathiine 2,2-dioxides.

The last few years have seen an explosion of interest in traditional photochromic systems not only for their applications in variable transmission devices, which continues to attract commercial interest, but also for the ability of these molecules to undergo structural and electronic reorganisation which has been seized upon by materials scientists for the development of switches, logic gates, photoinduced molecular motions such as rotors and fibrils, and photoregulation of drug availability. This comprehensive review examines, for the first time, the ‘dark side of photochromism’; negatively photochromic systems which are coloured in their ground state and reversibly photobleach upon exposure to electromagnetic radiation with a wavelength over ca. 400 nm i.e. visible light responsive systems. This review is organised by structural class and examines their synthesis, structure, key spectroscopic data for coloured and bleached species, structure – switching relationships and applications. The usefulness of these negatively photochromic systems is only gradually coming to the fore with the advantages of low energy activation c.f. conventional Uv-activated switches, enabling the modulation of a plethora of useful optical and physical properties and the design of new materials with broad ranging applications.

A series of novel 3-aryl-(3,3-diaryl-3 H- naphtho[2,1- b ]pyran-8-yl)-3 H -naphtho[2,1- b ]pyrans has been accessed from 6-bromo-2-naphthol via a four step transformation. Acylation of the dianion derived from the treatment of 6-bromo-2-naphthol with n -butyllithium with Weinreb amides and subsequent reaction with a 1,1,-diarylprop-2-yn-1-ol gave 8-aroyl-3 H -naphtho[2,1- b ]pyrans in good yield. Addition of lithium trimethylsilylacetylide to the foregoing 8-aroylnaphthopyrans proceeded smoothly with base-mediated desilyation to afford the target bi-naphthopyrans upon acid-catalysed reaction with 2-naphthol. Preliminary evaluation of the photochromic response of the new bi-naphthopyrans revealed reversible independent naphthopyran ring-opening leading to a complex photochromic signature.

3-Benzoylnaphtho[1,2-b]furan-5-ol forms a photochromic benzochromene upon reaction with a 1,1-diarylprop-2-yn-1-ol affording a red coloured photomerocyanine, with a half-life of 2.3 min, upon UV-irradiation. Retention of the initial 1,4-oxygenation pattern of the naphthalene moiety through replacement of the furan unit with a methoxy group led to a benzochromene, which developed a similar red colour upon UV-irradiation but was more persistent with a half-life of over 42 min. Treatment of the 3-benzoylnaphtho[1,2-b]furan-5-ol with a 1,1,3-triarylprop-2-yn-1-ol similarly afforded a benzochromene, which did not display any photochromism at ambient temperature as a consequence of steric interactions in the photomerocyanines. The synthesis of N-(5-hydroxynaphtho[1,2-d]thiazol-2-yl)acetamide, as a precursor to a photochromic hetero-fused benzochromene, by the mild selective deprotection of the O-acetyl group of 2-acetamidonaphtho[1,2-d]thiazol-5-yl acetate was complicated by a facile, competitive, oxidative dimerisation to afford a novel [2,2′-binaphthothiazole]-1,1′-diol.

1-Aryl-1-(2-bromophenyl)but-2-yn-1-ols, obtained from the addition of prop-1-yn-1-yllithium to 2-bromobenzophenones, readily rearrange to 4-aryl-4-(2-bromophenyl)but-3-en-2-ones upon treatment with TFA. Subsequent intramolecular Pd-mediated α-arylation of these but-3-en-2-ones gave 4-aryl-2-naphthols which were smoothly transformed into photochromic naphthopyrans.

The syntheses of a series of new ketohydrazone dyes and pigment lakes with a unique structural motif derived from 4-morpholino-2-naphthol are described. The morpholine substituent is responsible for the hypsochromically shifted absorption maxima with significantly enhanced molar extinction coefficients of the new dyes; this conclusion is supported by time-dependent DFT (TD-DFT) simulations. The location of the morpholine substituent at a sterically demanding site in the pigment lake obstructs further coordination of the bridging sulfonate groups in the solid state and prevents the formation of a 1-dimensional polymeric system, which is common for other pigment lakes.

A series of mono-, bis- and tris-4-(naphthopyran-3-yl)phenyl substituted methanols were efficiently synthesised using a 4-(naphthopyran-3-yl)phenyllithium intermediate. The resulting substituted methanols displayed good photochromism leading to the reversible generation of red–orange photomerocyanines. Acidic dehydration of the methanols gave intensely coloured cations which, upon subsequent UV irradiation, reversibly generated cationic photomerocyanines with long wavelength absorption maxima at ca. 640 nm.

1-Aryl-1-(2-bromophenyl)but-2-yn-1-ols, obtained from the addition of prop-1-yn-1-yllithium to 2-bromobenzophenones, readily rearrange to 4-aryl-4-(2-bromophenyl)but-3-en-2-ones upon treatment with TFA. Subsequent intramolecular Pd-mediated α-arylation of these but-3-en-2-ones gave 4-aryl-2-naphthols which were smoothly transformed into photochromic naphthopyrans.

Five bis(isocyanuric) acid dimers have been prepared and characterised. The introduction of flexible alkyl chains was necessary to aid solubility. On mixing with N,N-bis(4-tert-butyphenyl)melamine in THF followed by slow evaporation, a viscous gel can form which is interpreted as evidence for the assembly of an infinite 2-D hydrogen bonded network.

A series of ethynyl and aryl substituted porphyrins and the corresponding metallated derivatives have been synthesised and characterised.

The crystal structures of two lead containing porphyrins are described. Structure 1 contains unprecedented stacks of three metalloporphyrins. Each structure shows disorder of the Pb atoms which are situated out of the mean plane of the porphyrin ring.

A linear zinc porphyrin dimer has been used for the first time to stabilise two identical non-covalent aggregates by a combination of N -pyridyl zinc binding and hydrogen bonding. An improved multigram synthesis of 5,15-bis-(3,5-di- tert -butylphenyl)-10,20-bis(trimethylsilylethynyl)porphyrin is described.

Heating 4-methoxy-1-naphthol with a 1,1-diarylprop-2-yn-1-ol gave the 2,2-diaryl-6-methoxy-2H-naphtho[1,2-b]pyran together with the novel merocyanine, (E)-2-[30,30-bis(aryl)allylidene]-4-methoxynaphthalen-\ud 1(2H)-one. Brief UV-irradiation of the pyran favoured the formation of the (Z)-merocyanine with longer irradiation and/or acidic conditions favouring the (E)-isomer.

Some new donor–acceptor porphyrins have been prepared based on a metallated bis(ethynyl) porphyrin core. 4-(Dimethylamino)phenyl was used as the donor group and 4-nitrophenyl, 4-cyanophenyl and 5-nitrothiazoyl as the acceptor groups. Dipyrrylmethane was used for large scale porphyrin ring synthesis because the absence of methylene substituents reduces the difficulty of substituent scrambling that occurs during porphyrin synthesis.

The complexes [Pd(bcope)(OTf)2] (1a), where bcope is (C8H14)PCH2-CH2P(C8H14), and [Pd(tbucope)(OTf)2] (1b), where tbucope is (C8H14)PC6H4CH2P(tBu)2, catalyze the conversion of diphenylacetylene to cis- and trans-stilbene and 1,2-diphenylethane. When this reaction was studied with para-hydrogen, the characterization of [Pd(bcope)(CHPhCH2Ph)](OTf) (2a) and [Pd(tbucope)(CHPhCH2Ph)](OTf) (2b) was achieved. Magnetization transfer from the alpha-H of the CHPhCH2Ph ligands in these species proceeds into trans-stilbene. This process has a rate constant of 0.53 s-1 at 300 K in methanol-d4 for 2a, where DeltaH = 42 +/- 9 kJ mol-1 and DeltaS = -107 +/- 31 J mol-1 K-1, but in CD2Cl2 the corresponding rate constant is 0.18 s-1, with DeltaH = 79 +/- 7 kJ mol-1 and DeltaS = 5 +/- 24 J mol-1 K-1. The analogous process for 2b was too fast to monitor in methanol, but in CD2Cl2 the rate constant for trans-stilbene formation is 1.04 s-1 at 300 K, with DeltaH = 94 +/- 6 kJ mol-1 and DeltaS = 69 +/- 22 J mol-1 K-1. Magnetization transfer from one of the two inequivalent beta-H sites of the CHPhCH2Ph moiety proceeds into trans-stilbene, while the other site shows transfer into H2 or, to a lesser extent, cis-stilbene in CD2Cl2, but in methanol it proceeds into the vinyl cations [Pd(bcope)(CPh=CHPh)(MeOD)](OTf) (3a) and [Pd(tbucope)(CPh=CHPh)(MeOD)](OTf) (3b). When the same magnetization transfer processes are monitored for 1a in methanol-d4 containing 5 microL of pyridine, transfer into trans-stilbene is observed for two sites of the alkyl, but the third proton now becomes a hydride ligand in [Pd(bcope)(H)(pyridine)](OTf) (5a) or a vinyl proton in [Pd(bcope)(CPh=CHPh)(pyridine)](OTf) (4a). For 1b, under the same conditions, two isomers of [Pd(tbucope)(H)(pyridine)](OTf) (5b and 5b') and the neutral dihydride [Pd(tbucope)(H)2] (7) are detected. The single vinylic CH proton in 3 and the hydride ligands in 4 and 5 appear as strong emission signals in the corresponding 1H NMR spectra.

The synthesis, characterisation and thermal and photochemical reactivity of Ru(CO)2(PPh3)(dppe) 1 towards hydrogen are described. Compound proved to exist in both fac (major) and mer forms in solution. Under thermal conditions, PPh3 is lost from 1 in the major reaction pathway and the known complex Ru(CO)2(dppe)(H)2 2 is formed. Photochemically, CO loss is the dominant process, leading to the alternative dihydride Ru(CO)(PPh3)(dppe)(H)2 3. The major isomer of 3, viz. 3a, contains hydride ligands that are trans to CO and trans to one of the phosphorus atoms of the dppe ligand but a second isomer, 3b, where both hydride ligands are trans to distinct phosphines, is also formed. On the NMR timescale, no interconversion of 3a and 3b was observed, although hydride site interchange is evident with activation parameters of DeltaH(double dagger) = 95 +/- 6 kJ mol(-1) and DeltaS(double dagger) = 26 +/- 17 J K(-1) mol(-1). Density functional theory confirms that the observed species are the most stable isomeric forms, and suggests that hydride exchange occurs via a transition state featuring an eta2-coordinated H2 unit.

Pd(bcope)(OTf)2 (where bcope is (C8H14)PCH2CH2P(C8H14)) is shown to react with an alkyne in the presence of parahydrogen to form alkyl hydrides, such as Pd(bcope)(CHPhCH2Ph)(H), that are detectable by NMR spectroscopy because the proton resonances of the alkyl arm appear with strongly enhanced signal strengths.

The photochemical reaction of Ru(CO)(3)(L)(2), where L = PPh(3), PMe(3), PCy(3) and P(p-tolyl)(3) with parahydrogen (p-H(2)) has been studied by in-situ NMR spectroscopy and shown to result in two competing processes. The first of these involves loss of CO and results in the formation of the cis-cis-trans-L isomer of Ru(CO)(2)(L)(2)(H)(2), while in the second, a single photon induces loss of both CO and L and leads to the formation of cis-cis-cis Ru(CO)(2)(L)(2)(H)(2) and Ru(CO)(2)(L)(solvent)(H)(2) where solvent = toluene, THF and pyridine (py). In the case of L = PPh(3), cis-cis-trans-L Ru(CO)(2)(L)(2)(H)(2) is shown to be an effective hydrogenation catalyst with rate limiting phosphine dissociation proceeding at a rate of 2.2 s(-1) in pyridine at 355 K. Theoretical calculations and experimental observations show that H(2) addition to the Ru(CO)(2)(L)(2) proceeds to form cis-cis-trans-L Ru(CO)(2)(L)(2)(H)(2) as the major product via addition over the pi-accepting OC-Ru-CO axis.