Photophysical properties and photochemical rearrangement of single crystal salicylideneaniline in solution

Salicylideneaniline originally crystallized from a solution has lemon yellow color. Irradiation with near ultraviolet causes the color change from yellow to red. The red state changes spontaneously back to yellow in 2ms. This change is accelerated by visible light. Kinetic data are reported in the temperature range between 10 and 60 degrees C, for the dark fading reactions of the colored isomers formed by the near ultraviolet irradiation. Observed the decay kinetics was first order reactions. Activation energies and entropies of activation are reported for ethanol. The observation of T-T absorption and emission were complicated due to the colored isomer formation during the optical pumping.     

Spectral and thermal characterization of grown organic single crystal

The growth of semicarbazone of p-hydroxy benzaldehyde (SPHB) single crystal by slow evaporation solution growth technique is reported in this article. The grown crystal was subjected to powder XRD study to identify the crystalline nature. Single crystal XRD study was done to measure unit cell parameters and to confirm the crystal structure. In the presence of various functional groups of SPHB was identified by FTIR spectrum. Its optical behavior was examined by UV?CVis?CNIR spectrum and the crystal was found to have transparency in the region between 245 and 1100?nm. Thermal properties of the crystal were investigated using thermogravimetric and differential thermal analysis (TG-DTA), which indicated that the melting of the material occurred before decomposition. The nonlinear optical (NLO) property was tested by Kurtz?CPerry powder technique for second harmonic generations.     

ESR and cidep studies of the photochemical processes in benzoyl formic acid single crystal

The photolysis of a single crystal of benzoyl formic acid at 77 K yielded the ESR observation of three trapped radical pairs, and a transient CIDEP of the diffused ketyl radical.     

Photoaddressed liquid crystal devices

Photoaddressed liquid crystal spatial light modulator devices are described and discussed. The initial experimental behaviour of a GaAs photoaddressed ferroelectric liquid crystal spatial light modulator is reported and compared with a similar nematic liquid crystal device.     

Effective photochemical synthesis of an air-stable anthracene-based organic semiconductor from its diketone precursor

A diketone precursor of air-stable bis-2-thienyl-2,6-anthracene was prepared and quantitatively converted to the target acene by photoirradiation of the n-π^∗ absorption both in solution and as a film, in air.     

Selective nucleation and discovery of organic polymorphs through epitaxy with single crystal substrates.

Crystallization of 5-methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile (1), previously found to produce six conformational polymorphs from solution, on single-crystal pimelic acid (PA) substrates results in selective and oriented growth of the metastable "YN" (yellow needle) polymorph on the (101)(PA) faces of the substrate. Though the freshly cleaved substrate crystals expose (101)(PA) and (111)(PA) faces, which are both decorated with [101](PA) ledges that could serve as nucleation sites, crystal growth of YN occurs on only (101)(PA). Goniometry measurements performed with an atomic force microscope reveal that the (001)(YN) plane contacts (101)(PA) with a crystal orientation [100](YN)//[010](PA) and [010](YN)//[101](PA). A geometric lattice analysis using a newly developed program dubbed GRACE (geometric real-space analysis of crystal epitaxy) indicates that this interfacial configuration arises from optimal two-dimensional epitaxy and that among the six polymorphs of 1, only the YN polymorph, in the observed orientation, achieves reasonable epitaxial match to (101)(PA). The geometric analysis also reveals that none of the polymorphs, including YN, can achieve comparable epitaxial match with (111)(PA), consistent with the absence of nucleation on this crystal face. In contrast, sublimation of 1 on cleaved succinic acid (SA) substrates, which expose large (010)(SA) faces decorated with steps along [101](SA), affords growth of several polymorphs, each with multiple orientations, as well as oriented crystals of a new metastable polymorph on the (010)(SA) surfaces. The lack of polymorphic selectivity on (010)(SA) can be explained by the geometric lattice analysis, which reveals low-grade epitaxial matches between (010)(SA) and several polymorphs of 1 but no inherent selectivity toward a single polymorph. These observations demonstrate the sensitivity of crystal nucleation to substrate surface structure, the potential of crystalline substrates for selective nucleation and discovery of polymorphs, and the utility of geometric lattice modeling for screening of substrate libraries for controlling polymorphism.     

Applications of Tamm plasmon-liquid crystal devices

ABSTRACT

The Tamm-plasmon-polariton (TPP) occurs at the interface between a metallic film and the photonic-crystal (PC) substrate. Unlike conventional surface-plasmon-polariton (SPP), TPP can be directly excited by both the transverse electric (TE) and transverse magnetic (TM) electromagnetic waves without using additional coupling optics. The fact that the optical functionality of most plasmonics devices is determined after fabrication limits their applications. Tunable SPP devices by applying liquid crystals (LCs) have been widely demonstrated due to their large birefringence and easy controllability via external stimuli. However, actively tuning TPP is difficult because the localised electric field is between the metallic film and PC substrate, the change of refractive index above the metallic film has only small influences on TPP. This article is intended to briefly review recent progress towards using LCs for actively tuning TPP devices. Not only TPP devices can gain benefits from LCs, we will also discuss the applications of TPP for measuring the anisotropy of the alignment films of LC devices. The sensitivity of the proposed scheme will be discussed.     

Photonic crystal fibre as an optofluidic reactor for the measurement of photochemical kinetics with sub-picomole sensitivity

Photonic crystal fibre constitutes an optofluidic system in which light can be efficiently coupled into a solution-phase sample, contained within the hollow core of the fibre, over long path-lengths. This provides an ideal arrangement for the highly sensitive monitoring of photochemical reactions by absorption spectroscopy. We report here the use of UV/vis spectroscopy to measure the kinetics of the photochemical and thermal cis-trans isomerisation of sub-picomole samples of two azo dyes within the 19-μm diameter core of a photonic crystal fibre, over a path length of 30 cm. Photoisomerisation quantum yields are the first reported for "push-pull" azobenzenes in solution at room temperature; such measurements are challenging because of the fast thermal isomerisation process. Rate constants obtained for thermal isomerisation are in excellent agreement with those established previously in conventional cuvette-based measurements. The high sensitivity afforded by this intra-fibre method enables measurements in solvents in which the dyes are too insoluble to permit conventional cuvette-based measurements. The results presented demonstrate the potential of photonic crystal fibres as optofluidic elements in lab-on-a-chip devices for photochemical applications.     

Alignment modulation of azobenzene-containing liquid crystal systems by photochemical reactions

Recent progress in alignment modulation of azobenzene-containing liquid crystal systems by photochemical reactions has been reviewed by dividing the modulation methods into two types: phase transitions (order–disorder change) and change of liquid crystal directors (order–order change). First, photochemical phase transitions and alignment changes of liquid crystals in guest/host mixtures and polymers are summarized. Then, alignment control of liquid crystals by linearly polarized light and photoactive surface layers is discussed. Finally, recent applications of alignment change and photochemical phase transitions of liquid crystals in holographic technology and photomechanical effects are introduced. In addition, future possible applications for a variety of practical devices, such as display devices, optical switching and reversible optical image storage, are mentioned.     

Efficient photochemical electron transfer sensitization of homogeneous organic reactions

Photochemical electron transfer induced reactions have become an interesting tool in organic synthesis since transformations can be easily performed which are difficult or impossible with more conventional organic reactions. In this context, electron transfer sensitized reactions are frequently used since the sensitizer can be considered as a catalyst. Various intermediates such as radical ions with a variety of reaction possibilities are involved. Nevertheless, the reactions have been performed with high yields and high selectivities. Particular attention is paid to the stability of the sensitizer. Reaction steps regenerating the sensitizer from different intermediates are discussed. In photochemical electron donor and acceptor sensitized transformations, these steps are often part of the main reaction course. In other cases, co-sensitizers or mediators significantly enhance the efficiency of the transformations although the number of reactive intermediates is increased.     

Expeditious photochemical reaction toward the preparation of substituted chroman-4-ones

A facile photochemical preparation of 5-, 6-, and 7-substituted chroman-4-ones from aryl 3-methyl-2-butenoate esters is described. The two-phase base-catalyzed method relies upon two consecutive processes in one-pot reaction through a photo-Fries rearrangement and a based-catalyzed intramolecular oxa-Michael addition to afford the desired products.     

Adsorption of organic molecules on rutile TiO2 and anatase TiO2 single crystal surfaces

The interaction of organic molecules with titanium dioxide surfaces has been the subject of many studies over the last few decades. Numerous surface science techniques have been utilised to understand the often complex nature of these systems. The reasons for studying these systems are hugely diverse given that titanium dioxide has many technological and medical applications. Although surface science experiments investigating the adsorption of organic molecules on titanium dioxide surfaces is not a new area of research, the field continues to change and evolve as new potential applications are discovered and new techniques to study the systems are developed. This tutorial review aims to update previous reviews on the subject. It describes experimental and theoretical work on the adsorption of carboxylic acids, dye molecules, amino acids, alcohols, catechols and nitrogen containing compounds on single crystal TiO(2) surfaces.     

Computational characterization of organic photovoltaic devices

We present recent progresses on applying the theoretical models and computational tools in assessing the performance of organic solar cells, especially the bulk heterojunction solar cells. Both the continuum device model and the dynamic Monte Carlo model are developed to investigate the photocurrent-voltage characteristics based on the exciton and charge carrier dynamics. Insights into key factors influencing the organic photovoltaic performances have been gained from these studies.     

Single crystal EPR studies of an organic NLO material: methyl-p-hydroxy benzoate

Single crystals of an organic nonlinear optical (NLO) material methyl-p-hydroxy benzoate (MHB) were grown by solvent evaporation technique. EPR spectra were recorded for Er3+: MHB and gamma-irradiated MHB at room temperature at X-band frequencies. The angular variation studies of the spectra were observed and the principal values of g were determined. The grown crystals were characterized by single crystal X-ray diffraction studies.     

Vibrational spectroscopic studies of an organic non-linear optical crystal 8-hydroxyquinolinium picrate

8-hydroxyquinolinium picrate (8-HQP) was synthesized by the addition of equimolar quantities of 8-hydroxyquinoline (8-HQ) and picric acid (PA). Single crystals were grown from N,N dimethyl formamide (DMF) by restricted evaporation method at room temperature. The solubility of 8-HQP was determined in different solvents at various temperatures. The structural characterization of the grown crystals was carried out by X-ray diffraction. Vibrational modes were classified on the basis of group theoretical analysis and the spectral bands were compared with those of parent compounds in order to propose a tentative assignment by recording FT-IR, FT-Raman and polarized Raman spectra in different crystal orientations. The crystal possess lower cut-off at 230 nm and good transparency as confirmed by optical transmittance studies.     

Scanning-induced growth on single crystal calcite with an atomic force microscope

We report observations of localized growth on the (1014) surface of single-crystal CaCO3 in supersaturated solutions while scanning with the tip of an atomic force microscope (AFM). At low contact forces, AFM scanning strongly enhances deposition along preexisting steps. This enhancement increases rapidly with increasing solution supersaturation, and is capable of filling in multilayer etch pits to produce defect-free surfaces at the resolution of the AFM. Attempts to achieve similar deposition rates in the absence of scanning require high supersaturations that produce three-dimensional crystal nuclei, which are important defects. Localized deposition produced by drawing the AFM tip back and forth across step edges can produce monolayer deposits extending well over a micron from the scanned area. These tip-induced deposits provide convincing evidence for the importance of ledge diffusion in calcite crystal growth.     

Kinetic determination of organic vapor mixtures with single piezoelectric quartz crystal sensor using artificial neural networks

A single piezoelectric quartz crystal coated with one kind of crown ether was applied to the simultaneous determination of binary acid and amine vapor mixtures. From the adsorption and desorption curves of analytes, which were somewhat different in shape, frequency shifts from ten time windows were taken as inputs for artificial neural networks (ANN). Prediction results were satisfactory for ANN in both sample sets. The average relative errors, for formic acid and acrylic acid were 5%, for n-butylamine and aniline, they were 3% with ANN respectively. The effects of number of neurons in the hidden layer of ANN on the performance of the network are also discussed.     

Formation of organic monolayers on silicon via gas-phase photochemical reactions

A new method for the formation of molecular monolayers on silicon surfaces utilizing gas-phase photochemical reactions is reported. Hydrogen-terminated Si(111) surfaces were exposed to various gas-phase molecules (hexene, benzaldehyde, and allylamine) and irradiated with ultraviolet light from a mercury lamp. The surfaces were studied with in situ Fourier transform infrared spectroscopy, high-resolution electron energy loss spectroscopy, and scanning tunneling microscopy. The generation of gas-phase radicals was found to be the initiator for organic monolayer formation via the abstraction of hydrogen from the H/Si(111) surface. Monolayer growth can occur through either a radical chain reaction mechanism or through direct radical attachment to the silicon dangling bonds.