Excited-state intramolecular proton transfer molecules bearing o-hydroxy analogues of green fluorescent protein chromophore

o-Hydroxy analogues, 1a-g, of the green fluorescent protein chromophore have been synthesized. Their structures and electronic properties were investigated by X-ray single-crystal analyses, electrochemistry, and luminescence properties. In solid and nonpolar solvents 1a-g exist mainly as Z conformers that possess a seven-membered-ring hydrogen bond and undergo excited-state intramolecular proton transfer (ESIPT) reactions, resulting in a proton-transfer tautomer emission. Fluorescence upconversion dynamics have revealed a coherent type of ESIPT, followed by a fast vibrational/solvent relaxation (<1 ps) to a twisted (regarding exo-C(5)-C(4)-C(3) bonds) conformation, from which a fast population decay of a few to several tens of picoseconds was resolved in cyclohexane. Accordingly, the proton-transfer tautomer emission intensity is moderate (0.08 in 1e) to weak (～10(-4) in 1a) in cyclohexane. The stronger intramolecular hydrogen bonding in 1g suppresses the rotation of the aryl-alkene bond, resulting in a high yield of tautomer emission (Φ(f) ≈ 0.2). In the solid state, due to the inhibition of exo-C(5)-C(4)-C(3) rotation, intense tautomer emission with a quantum yield of 0.1-0.9 was obtained for 1a-g. Depending on the electronic donor or acceptor strength of the substituent in either the HOMO or LUMO site, a broad tuning range of the emission from 560 (1g) to 670 nm (1a) has been achieved.     

Mesogenic and optical properties of α,α′‐bis(4‐alkoxyphenylethynyl)oligothiophenes

Liquid crystalline α,α′‐bis(4‐alkoxyphenylethynyl)oligothiophenes (bi‐ and ter‐thiophene) have been synthesized and their mesogenic behaviour and optical properties investigated. They all exhibited a nematic mesophase, and compounds with long alkoxy chains also showed lamellar phases. Increasing the number of thiophene units increased both the transition temperatures and the mesophase ranges. As for their optical properties, incorporating more thiophene units results in red‐shifted absorption and emission spectra, slightly enhanced quantum efficiency, and a larger Stoke's shift. Most importantly, in terms of the absorption and emission maxima, the incorporation of one 4‐alkoxyphenylethynyl moiety was found to be equivalent to adding one thiophene ring.     

THEN FILM CELLS BASED ON CuInSe2

Abstract

Using thin film devices of the form CdS(n)/CuInSe₂(p) fabricated on electrodeposited CuInSe₂, electrical and optical measurements have been made. From temperature-dependent I-V measurements, it was observed that the recombination current became progressively more important as the temperature was decreased. Results of dark C-V measurements indicated that CuInSe₂ films with carrier concentrations in the range from 10¹⁵ to 10¹⁷ cm^?3 can be easily prepared using the electrodeposition method. Photoresponse of the devices was also measured, giving an essentially flat region in the range from 0.6 to 1.0 micron. At wavelengths beyond 1 micron, the quantum efficiency decreased continuously with the increase in the wavelength. This continuous decrease in the quantum efficiency could be due to the presence of interface states as suggested by the photo capacitance measurements.     

Spiro‐Configured Bipolar Host Materials for Highly Efficient Electrophosphorescent Devices

In this study, we synthesized and characterized a series of spirobifluorene‐based bipolar compounds (D2 ACN, DNPACN, DNTACN, and DCzACN) in which a dicyano‐substituted biphenyl branch, linked orthogonally to a donor biphenyl branch bearing various diarylamines, acted as an acceptor unit allowing fine‐tuning of the morphological stability, triplet energy, bipolar transport behavior, and the HOMO and LUMO energy levels. The promising physical properties of these new compounds, together with their ability to transport electrons and holes with balanced mobilities, made them suitable for use as host materials in highly efficient phosphorescent organic light‐emitting diodes (PhOLEDs) with green iridium‐based‐ or red osmium‐based phosphors as the emitting layer (EML). We adopted a multilayer structure to efficiently confine holes and electrons within the EML, thus preventing exciton diffusion and improving device efficiency. The device incorporating D2 ACN doped with the red emitter [Os(bpftz)₂(PPhMe₂)₂] (bpftz=3‐(trifluoromethyl)‐5‐(4‐tert‐butylpyridyl)‐1,2,4‐triazolate) gave a saturated red electrophosphorescence with CIE coordinates of (0.65, 0.35) and remarkably high efficiencies of 20.3 % (21 cd A^?1) and 13.5 Lm W^?1 at a practical brightness of 1000 cd m^?2.     

A Generalized Unpaired Electron Spin Density Equation and Organic Hyperconjugation Mechanism

A large class of stereochemcial and related interactions in organic chemistry are repulsive and others are attractive, but the relative orientation of two methyl groups and the amount of energy required to twist one relative to the other (the hindered rotation energy barriers), or the alignment of such a group with respect to a conjugated ring to which it is attached (widely attributed to a mechanism called “hyperconjugation”) are estimated to be small in compared with the total energy of the molecule. We used theories of both isotropic and anisotropic proton hyperfine interactions in the π‐electron systems developed in the early sixties. They are approximated by the magnetic dipole nteractions between each proton and an electron spin magnetization that is distributed in 2s and 2p Slater atomic orbitals center on carbon atoms. We have extended these theories to the non‐planar olefinic cation radicals, which are very important in biochemistry as well as in petroleum catalysis. A three dimensional electron spin density equation has been developed in this paper to handle some Jahn‐Teller vibronic molecules. The new electron spin density equation related the observed proton hyperfine splittings to the non‐planar structures of the open‐chain alkene cation radicals generated by radiolysis and various chemical oxidation methods. The spin densities and the conformational calculations based on valence bond theory and symmetry principles are compared with some more elaborated molecular orbital calculations in the literature. The localized valence bond approaches are better in accord with our experimental results. The anomalous line‐width effect of the four methyl groups observed in the 2,3‐dimethyl‐2‐butene cation radicals also confirmed the positive sign of the electron‐proton hyperfine constant of hyper‐conjugation mechanism. A methyl substituent attached to a conjugated molecule often behaves as if it formed part of the region of conjugation; the charge appears to flow from the methyl group into the π electron system and it may also give rise to an appreciable dipole moment. Methylation also gives rise to an appreciable dipole moment, and the resultant red shift of electronic absorption bands is of some importance in the design of dye molecules.     

Sorption interactions of volatile organic compounds with organoclays under different humidities by using linear solvation energy relationships

Organoclays are usually used as sorbents to reduce the spread of organic compounds and to remove them at contaminated sites. The sorption equilibrium and the mechanisms of volatile organic compounds (VOCs) on organoclays under different humidities are helpful for developing efficient organoclays and for predicting the fate of VOCs in the environment. In this study, the organoclay was synthesized through exchanging inorganic cations by hexadecyltrimethyl ammonium (HDTMA) into montmorillonite, resulting in 12?% of organic content. The surface area of organoclay was smaller than the unmodified clay due to the incorporation of organic cations into the interlayer. Both adsorption on organoclay surface and partition into the incorporated HDTMA in organoclay played roles on the sorption process. Compared the sorption coefficients in montmorillonite and different modified clays, the incorporated organic cations overcame the inhibition effect of hydrophilic surface of clay on the sorption process of hydrophobic organic compounds from water. The sorption coefficients of VOC vapors on organoclay were further characterized using a linear solvation energy relationship (LSER). The fitted LSER equations were obtained by a multiple regression of the sorption coefficients of 22 probe chemicals against their solvation parameters. The coefficients of the five-parameter LSER equations showed that high HDTMA-content montmorillonite interacts with VOC molecules mainly through dispersion, partly through dipolarity/polarizability and hydrogen-bonds as well as with negative π-/n-electron pair interaction. The interaction analysis by LSERs suggests that the potential predominant factors governing the sorption of VOCs are dispersion interactions under all tested humidity conditions, similar with the lower level modified clay. The derived LSER equations successfully fit the sorption coefficients of VOCs on organoclay under different humidity conditions. It is helpful to design better toxic vapor removal strategy and evaluate the fate of organic contaminants in the environment.     

Preparation and application of cryptand-coated piezoelectric crystal gas-chromatographic detector

A re-usable and sensitive cryptand-22-coated quartz-crystal membrane piezoelectric sensor with a homemade computer interface for signal acquisition and data processing was prepared and applied as a gas-chromatographic (GC) detector for various organic molecules. The oscillating frequency of the quartz crystal decreased due to the adsorption of organic molecules on cryptand-22. Effects of functional group, molar mass, steric hindrance and polarity of organic molecules on frequency responses of the cryptand-coated piezoelectric crystal detector were investigated. The cryptand-coated piezoelectric crystal GC detector had demonstrated high sensitivity for various polar organic molecules and good reproducibility when re-used. The frequency responses of the cryptand-coated crystal for various molecules were in the following order: carboxylic acids (RCOOH)primary amines (R-NH₂)>alcohols (ROH)>secondary amines (R₂NH)>tertiary amines (R₃N)>ketones. More polar molecules exhibited better frequency responses. The effect of temperature and amount of coating on the frequency responses of cryptand-coated crystal GC detector were also investigated. The cryptand-coated piezoelectric crystal GC detector compared well with the commercial thermal conductivity detector (TCD).