Andrew J. Kay

Optically switchable diffraction grating in a photochromic/polymer thin film.

An optically switchable diffraction grating has been made in a thin film containing a photochromic dye and amorphous polycarbonate. We show that a film containing the dye 5-chloro-1,3-dihydro-1,3,3-trimethylspiro[2H-indole-2,3-(3H)naphth[2,1-b](1,4)oxazine] can be optically processed so that a diffraction grating can be completely switched on by ultraviolet light and turned off by thermal relaxation. The ability to switch or modulate the diffraction efficiency has a number of practical applications that include optical switches and add/drop multiplexers.

Light losses from scattering in luminescent solar concentrator waveguides

The reductions in the transmission of emission originating from a fluorophore dissolved in a polymer matrix due to light scattering were compared in two forms of planar waveguides used as luminescent solar concentrators: a thin film of poly(methylmethacrylate) (PMMA) spin-coated on a glass plate and a solid PMMA plate of the same dimensions. The losses attributable to light scattering encountered in the waveguide consisting of the thin film of polymer coated on a glass plate were not detectable within experimental uncertainty, whereas the losses in the solid polymer plate were significant. The losses in the solid plate are interpreted as arising from light-scattering centers comprising minute bubbles of vapor/gas, incomplete polymerization or water clusters that are introduced during or after the thermally induced polymerization process.

2-{2-[5-(4-Cyano-5-di-cyano-methyl-idene-2,2-dimethyl-2,5-di-hydro-furan-3-yl)penta-2,4-dienyl-idene]-3,3-dimethyl-2,3-di-hydro-1H-indol-1-yl}ethyl 3,5-bis-(benz-yloxy)benzoate.

In the title molecule, C48H42N4O5, a potential non-linear optical compound, the furan ring [r.m.s. deviation = 0.010u2005(1)u2005Å] and the indolylidene ring system [r.m.s. deviation = 0.013u2005(2)u2005Å] are inclined to one another by 18.52u2005(6)°. This is similar to the arrangement [16.51u2005(18)°] found for the N-hydroxyethyl adduct of the title compound [Bhuiyan et al. (2011 ▶). Mol. Cryst. Liq. Cryst. 548, 1–12]. Replacing the hydroxyethyl group with 3,5-dibenzyloxybenzoate has not resulted in a non-centrosymmetric lattice arrangement or significant changes to the basic molecular structure. In the crystal, molecules are linked via pairs of C—H⋯N hydrogen bonds, forming inversion dimers with an R 2 2(20) ring motif. The dimers are linked via C—H⋯O hydrogen bonds, forming C(17) chains along [010]. The chains are linked by further C—H⋯N hydrogen bonds, forming layers parallel to (001) and enclosing R 2 2(44) ring motifs. There are also C—H⋯π interactions present, stabilizing the interlayer orientation of the pendant bis(benzyloxy)benzoyloxy group.

Photoinitiators for two-photon polymerisation: effect of branching and viscosity on polymerisation thresholds

A series of multi-branched two-photon photoinitiators (PIs) based around the well-known triphenylamine donor core were synthesised for use in two-photon polymerisation (TPP) and are designated as compounds 6, 7 and 8. The use of a phenylene-vinylene π-system was used with an ethyl ester acceptor moiety which gives dipolar (6), quadrupolar (7) and octupolar (8) branching. Two-photon absorption cross-sections (δ2PA) of 126 GM, 358 GM and 590 GM were measured at 780 nm for 6, 7 and 8, respectively. The fluorescence quantum yields (ϕF) were determined in both MeOH and the acrylate system employed for TPP, and demonstrate the impact of viscosity upon photophysical properties of multi-branched molecules. Excellent polymerisation thresholds were demonstrated in the μW region: namely 45 μW (6), 61 μW (7) and 27 μW (8) at a writing speed of 50 μm s−1. Finally, an explanation for the disparity of polymerisation thresholds is proposed for these PIs and provides insight into the future development of low threshold PIs for TPP.

Design, synthesis, and characterization of photoinitiators for two-photon polymerization

A series of dipolar and quadrupolar two-photon absorption (2PA) photoinitiators (PIs) based around the well-known triphenylamine (TPA) core and tricyanofuran (TCF) acceptors have been prepared for use in two-photon polymerisation (TPP). The synthesised dipolar species are designated as 5 and 7, and the remaining quadrupolar species are 6, 8, 9 and 10. Large two-photon absorption cross-sections (δ2PA) ranging between 333 - 507 GM were measured at 780 nm using the z-scan technique. Fluorescence quantum yields (ΦF) were below 3% across the series when compared to Rhodamine 6G as a reference standard. Finally, TPP tests were conducted on PIs 7 and 8 to assess their ability to initiate the polymerisation of acrylate monomers using an 800 nm femtosecond Ti:Sapphire laser system.

2-(3-Cyano-4-{3-[1-(2-hy­droxy­eth­yl)-3,3-dimethyl-1,3-di­hydro­indol-2-yl­idene]prop-2-en­yl}-5,5-dimethyl-5H-furan-2-yl­idene)malono­nitrile

The title compound, C25H24N4O2, adopts a cisoid configuration and has twofold orientational disorder of the 2-hydroxyethyl group. The molecule is twisted from planarity so that the dihedral angle between the terminating indol-2-ylidene and the furan-2-ylidene moiety mean planes is 12.75u2005(7)°. Conformational disorder occurs at the indol-2-ylidene N atom, which results in two orientations for the hydroxyethyl group [occupancy ratio = 0.896u2005(2):0.104u2005(2)], and the hydroxy O atom of the 2-hydroxyethyl group is located over three sites [occupancy ratio = 0.548u2005(2):0.348u2005(2):0.104u2005(2)]. An intramolecular C—H⋯O hydrogen bond involving the lowest occupancy hydroxy O atom is observed. In the crystal, the molecules pack in parallel dimeric sheets about centres of symmetry, utilizing O—H⋯N(cyano), C—H⋯N(cyano) and O—H⋯O hydrogen bonds, in two sets parallel to (02-1) and (021) planes.

1-(2,3-Di­hydroxy­prop­yl)-4-{2-[4-(di­methyl­amino)­phen­yl]vin­yl}pyridinium chloride

The title compound, C18H23N2O2 +·Cl−, crystallizes with two independent cations and anions per cell. Each cation has twofold rotational disorder about the linking vinyl groups but with unequal occupancies [0.963u2005(5):0.037u2005(5) and 0.860u2005(8):0.140u2005(8)]. The two independent cations are close to being related by an inversion centre but the data does not support the expected centrosymmetric space-group assignment. The conclusion is that the differing rotational disorder has lead to an overall non-centrosymmetric lattice. In the crystal, the molecules pack in layers parallel to (133) and (-13-3), chain-linked with motif C 1 2(7) by the dihydroxypropyl O–H⋯Cl⋯H–O hydrogen bonds. Other lattice binding is provided by O—H⋯Cl, C—H⋯Cl and C—H⋯N interactions.

Investigation of third order nonlinear optical properties in s-indacene-1,3,5,7(2H,6H)-tetraone based D-π-A-π-D chromophores by z-scan

Here we describe the synthesis and characterization of a series of centro-symmetric D-π-A-π-D chromophores based on an s-indacene-1,3,5,7(2H,6H)-tetraone acceptor with conjugated linkers containing thiophene and pyrrole moieties. These materials were studied by UV visible absorption spectroscopy and their third order nonlinear optical properties investigated by z-scan at 1064 nm. The introduction of conjugated pyrrole linkers was found to give an effective third order hyperpolarizability of -1.54 x10-30 esu, and an effective two photon absorption cross section of 6100 GM at 1064 nm. As these chromophores showed comparatively high effective nonlinear absorption they have potential in photonic applications such as optical limiting, optical communication, and for two photon initiated polymerization.

2-(3-Cyano-4-methyl-5,5-diphenyl-5H-furan-2-yl-idene)malono-nitrile.

The title compound, C21H13N3O, crystallizes with two independent molecules with similar conformations per asymmetric unit. The dihydrofuran rings are essentially planar with maximum deviations of 0.017u2005(1) and 0.006u2005(1)u2005Å for the O atoms. The dihedral angles between the dihydrofuran ring and the attached phenyl rings are 79.90u2005(6) and 82.07u2005(6)° in one molecule and 79.36u2005(6) and 72.26u2005(6)° in the other. In the crystal, the molecules are linked by weak C—H⋯π and C—H⋯N interactions similar to those in other closely related crystals. The replacement of appended methyl by phenyl groups has not significantly affected the dihydrofuran ring structure or the crystal packing interactions.

1-(4-{[(1,3,3-Tri­methyl­indolin-2-yl­idene)meth­yl]diazen­yl}phen­yl)ethanone

The title compound, C20H21N3O, has crystallographic mirror symmetry with all non-H atoms apart from the methyl C atom of the CMe2 group lying on the mirror plane. Molecules are linked into planar sheets parallel to (010) by phenyl–azo C—H⋯N and phenyl–ethanone C—H⋯O interactions. Methyl C—H⋯π interactions provide crosslinking between the planes.