Anthony D. Woolhouse

Solid state dye lasers based on 2-hydroxyethyl methacrylate and methyl methacrylate co-polymers

Abstract The laser performance of a range of solid state dye lasers based on rhodamine 590-doped co-polymers of 2-hydroxyethyl methacrylate (HEMA) and methyl methacrylate (MMA) has been investigated. The optimisation of preparation conditions, including polymerisation initiator and solvent for dye delivery is discussed in detail. Laser efficiency is compared for different polymeric hosts and dye concentrations with a range of output couplers, cavity lengths and repetition rates. Passive and dynamic loss have been determined for each host medium. Laser efficiencies of optimised polymers are among the highest reported for rhodamine 590-doped solid state dye lasers under these operating conditions. Highest slope efficiency of 35% and lowest threshold fluence of 0.06 J cm −2 were obtained with dimethyl sulphoxide (DMSO) additive in MPMMA at 10 Hz repetition rate.

A simple, novel method for the preparation of polymer-tetherable, zwitterionic merocyanine NLO-chromophores

A suite of polymer-ready nonlinear optical merocyanines has been synthesised and characterised. The tethering functionality—a vicinal dihydroxypropyl residue—is introduced onto the donor nitrogen of the chromophore precursor without the need for protection/deprotection steps, thereby giving ready access to potentially high Tg condensation polymer systems. An X-ray crystal structure determination on a representative chromophore 5 confirms the largely zwitterionic nature of these systems and experimental measurements of second-order nonlinear response [β(0)], by hyper-Raleigh scattering, indicate that a pyridylidene donor–quinomethide acceptor combination gives rise to the largest nonlinearity.

Simple zwitterionic merocyanines as potential NLO chromophores

A suite of zwitterionic pyridylidene-based merocyanines that contain no interconnecting π-bridge between the donor and acceptor rings has been synthesised and their second-order NLO properties evaluated largely by semi-empirical computational methods (MOPAC 97/AM1). Contrary to expectation, increasing the degree of inter-ring twist (θ), at least up to 55°, in these new pyridylideneazolone chromophores is found to have little or no effect on the figure of merit [μβ(0)]. An X-ray crystallographic appraisal of one of these chromophores, 14, reveals however that the twist angle (albeit in the solid state) is greater than that predicted by computation and that all other features are consistent with the highly zwitterionic nature of these systems. In spite of this, a combination of factors—insufficient acceptor strength, insufficient extent of conjugation and perhaps insufficient twist angle, in particular—clearly leads to the low values of the quadratic hyperpolarisabilities. The trade-off between targeting a more modest β from a minimum of π-conjugating framework between D and A (and therefore synthetic expediency) and seeking a moderate-to-high dipole moment has therefore resulted in only low figures of merit for these systems.Calculations performed on a suite of readily accessible, isoelectronic cyanines, in which the acceptor is a stabilised cyclopentadienide carbocycle rather than a heterocycle, have revealed the potential that these systems, exemplified by 27, have as NLO chromophores. Representative polymer-tetherable derivatives of this system have been prepared as have the corresponding TDI-based polyurethanes.

Thermal and optical properties of polymer hosts for solid-state dye lasers

We present measurements of thermal and optical properties of poly(methyl methacrylate) (PMMA), PMMA modified by the addition of ethanol (MPMMA), and copolymers of methyl methacrylate with 2-hydroxyethyl methacrylate [P(HEMA:MMA)]. Spectral transmission of the polymers is excellent (alpha = 0.5 cm(-1) at 400 nm, decreasing to 0.04 cm(-1) at 633 nm). Measured laser damage thresholds of MPMMA and P(HEMA:MMA) show at least a twofold increase over PMMA. Thermal lensing measured in these hosts doped with Rhodamine 6G is shown to be similar (f = -450 mm for pump power of 200 mW in a 2-mm-diameter spot, scaling with pump intensity). Compared with MPMMA, P(HEMA:MMA) offers an improved surface quality and a more uniform dye distribution.

Synthesis and linear/nonlinear optical properties of a new class of ?RHS? NLO chromophoreElectronic supplementary information (ESI) available: synthesis and characterisation data. See http://www.rsc.org/suppdata/jm/b3/b315274j/

Examples of a new class of zwitterionic, “right-hand side” merocyanines containing a cyanodicyanomethylidenedihydrofuran electron acceptor have been prepared. As well as allowing for the facile synthesis of these chromophores, our synthetic methodology enables considerable variation in both the donor moiety as well as the extent of conjugation between the donor and acceptor systems. As expected, all of these “right-hand side” systems are negatively solvatochromic, with the difference between λmax (polar vs. nonpolar solvents) increasing with the extent of conjugation. In accord with expectations, hyper-Raleigh scattering (HRS) measurements confirm that molecules with the greatest conjugation pathway (for e.g.21c, 23c) have the largest first hyperpolarisabilites, βo. In addition, our HRS evaluation indicates that the 4-quinolinylidene donor nucleus is superior to both the 4-pyridinylidene and benzothiazolylidene systems. The figures of merit, μ(calc).βo(measured), that we obtain for some of these compounds, are of a similar magnitude to the best “left hand side” examples reported in the literature. In order to demonstrate the versatility of our synthetic technique, representative polymer-tetherable derivatives of these compounds have been prepared, as have the corresponding TDI-based polyurethanes.

ORIENTATION AND SOLVATOCHROMISM OF DYES IN LIQUID CRYSTALS

The orientation and solvatochromism of some dye molecules in a liquid crystal have been investigated. Interactions with the host and the structure of the dye molecule affect the macroscopic alignment of dichroic dye molecules in a liquid crystal. It was observed that some dye molecules show a large bathochromic shift of their absorption maxima in the liquid crystal host relative to the situation in isotropic solvents. It is suggested that this is due to the occurrence of a much weaker reaction field in the anisotropic, rigid host. These dye molecules show little or no apparent order in the anisotropic host despite the observation of a reduction in the electro optic switching time when the dye is present. The highest degree of macroscopic alignment was observed for a merocyanine compound, which showed the smallest solvatochromic shift in the liquid crystal host. These results are discussed in terms of the steric, dipolar and hydrogen bond interactions between the guest and the host.

Characterization of dye-doped media for real-time holography

Abstract Studies of saturable dyes used as holographic media where saturation gives rise to both amplitude and phase holograms are presented. Using a simple absorption model together with the Kramers-Kronig relation, a theory for the prediction of holographic diffraction efficiencies over a range of read-wavelengths was developed. Results of experimental tests are presented as support for the model.

Transition state analogue inhibitors of human methylthioadenosine phosphorylase and bacterial methylthioadenosine/S-adenosylhomocysteine nucleosidase incorporating acyclic ribooxacarbenium ion mimics.

Several acyclic hydroxy-methylthio-amines with 3-5 carbon atoms were prepared and coupled via a methylene link to 9-deazaadenine. The products were tested for inhibition against human MTAP and Escherichia coli and Neisseria meningitidis MTANs and gave K(i) values as low as 0.23 nM. These results were compared to those obtained with 1st and 2nd generation inhibitors (1S)-1-(9-deazaadenin-9-yl)-1,4-dideoxy-1,4-imino-5-methylthio-D-ribitol (MT-Immucillin-A, 3) and (3R,4S)-1-[9-deazaadenin-9-yl)methyl]3-hydroxy-4-methylthiomethylpyrrolidine (MT-DADMe-Immucillin-A, 4). The best inhibitors were found to exhibit binding affinities of approximately 2- to 4-fold those of 3 but were significantly weaker than 4. Cleavage of the 2,3 carbon-carbon bond in MT-Immucillin-A (3) gave an acyclic product (79) with a 21,500 fold loss of activity against E. coli MTAN. In another case, N-methylation of a side chain secondary amine resulted in a 250-fold loss of activity against the same enzyme [(±)-65 vs (±)-68]. The inhibition results were also contrasted with those acyclic derivatives previously prepared as inhibitors for a related enzyme, purine nucleoside phosphorylase (PNP), where some inhibitors in the latter case were found to be more potent than their cyclic counterparts.

Efficient, high photostability, high brightness, co-polymer solid state dye lasers

Abstract We report an investigation of the laser beam quality, efficiency and photostability of rhodamine 590 solid state dye lasers with hosts based upon 2-hydroxyethylmethacrylate and methylmethacrylate P(HEMA:MMA) co-polymers and modified methylmethacrylate (MPMMA) polymers with ethanol and dimethylsulphoxide additives. Highest efficiencies were obtained with MPMMA, with slope efficiencies of up to 44% (corresponding to 61% optical-optical conversion) measured for ethanolic MPMMA. P(HEMA:MMA) hosts gave superior photostability, with the highest normalized photostability of 240 GJ mol−1 obtained for a P(HEMA:MMA) 1:1 rod. A simple resonator has been used to compensate the effects of thermal lensing and pump mode-mismatch, resulting in optimized beam quality for MPMMA lasers.

The first-order hyperpolarizabilities of some charge transfer conjugated molecules with high transmission in the far red

Abstract The first-order hyperpolarizabilities, β, of a number of novel merocyanine compounds bearing electron donor and acceptor groups at opposite ends of the molecules have been determined using hyper-Rayleigh scattering. The values of β increased with increasing strength of the electron acceptors and extent of conjugation including the molecular moiety linking the donor and acceptor groups. Furthermore, the non-aromatic 1,4 dihydropyridyl donor gives a greater β value than the benzothiazole donor.