Craig J. Wilson

Synthesis and linear and nonlinear optical properties of low-melting π-extended porphyrins

A large and diverse library of trans-A2B2 and A2BC-porphyrins possessing two arylethynyl substituents at the meso positions has been efficiently synthesized and tested for their two-photon absorption (2PA) behavior. All compounds fall into three general types A–π–A, D–π–D or D–π–A, where A is an electron-acceptor and D is an electron-donor moiety. These porphyrins contain two polyalkoxyaryl substituents, resulting in very low melting points (typically 110–125 °C) and superb solubility in non-polar solvents. Some of these porphyrins exhibit two different crystal phases in addition to an isotropic liquid state. Their linear and nonlinear optical properties were thoroughly elucidated and analyzed. π-Extended porphyrins emit light in the NIR and have moderate triplet state lifetimes. The increase of 2PA cross-section in the Soret region for porphyrins bearing strong electron-donating groups has been attributed to resonance enhancement (caused by intensification, redshift and broadening of the lowest Q-band) of gerade–gerade transition. The combination of high two-photon absorption cross-sections (>500 GM) and low melting points makes them perfect candidates for nonlinear optical materials in the 600–900 nm range.

Two-photon absorption in butadiyne-linked porphyrin dimers: torsional and substituent effects

Dyes exhibiting efficient two-photon absorption (2PA) are in demand for a wide range of applications, and meso–meso butadiyne-linked porphyrin dimers (bis-porphyrins) are promising chromophores in this area. As part of an investigation of the structure–property relationships controlling the performance of these dyes, we present the synthesis of eight π-extended dimers, with substituents providing diverse push and pull electronic effects, and high solubility. We show that the peak 2PA cross sections can be increased from 3000 GM to 20 000 GM by attaching terminal electron-withdrawing or -donating groups, and by converting the free-base dimers to zinc complexes. The two-photon excited fluorescence spectra of porphyrin dimers in viscous media, under conditions such that excited states do not planarize prior to emission, reveal that dimers in planar conformations dominate the two-photon absorption.

Amplified Two-Photon Absorption in Trans-A2B2-Porphyrins Bearing Nitrophenylethynyl Substituents

We show that peripheral nitro groups enhance the maximum two-photon absorption cross-section of trans-A(2)B(2)-porphyrins bearing two phenylethynyl substituents by more than one order of magnitude. Maximum values as high as 1000 GM result from realization of suitable conditions for effective resonance enhancement along with a lowering of the energy and intensification of the two-photon allowed transitions in the Soret region.

New metathesis routes to layered dichalcogenides: synthesis, crystal growth and structure of NayNbX2 (y=0.5, X = S, Se)

Separated reactant metathesis methods using ternary oxide precursors and yttrium chalcogenides have been used to prepare powders and crystals of alkali metal niobium dichalcogenides, AyNbX2 (X = S, Se). The structure of Na0.5NbSe2 has been solved unambiguously for the first time from single crystal X-ray data (hexagonal space group P63/mmc (no. 194), a = 3.4762(7), c = 15.342(2) A, U = 160.55(5) A3, Z = 2). Similarly, the structure of Na0.5NbS2 has also been determined (hexagonal space group P63/mmc, a = 3.3533(4), c = 14.547(3) A, U = 141.66(4) A3, Z = 2). Products have been characterised further by powder X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis. Magnetic measurements describe temperature-independent paramagnetic behaviour for both dichalcogenides, with no superconducting transitions above 1.8 K.