Excited State Intramolecular Proton Transfer in Ethynyl‐Extended Regioisomers of 2‐(2′‐Hydroxyphenyl)benzothiazole: Effects of the Position and Electronic Nature of Substituent Groups

Although the organic dyes based on excited state intramolecular proton transfer (ESIPT) mechanism have attracted significant attention, the structure‐property relationship of ESIPT dyes needs to be further exploited. In this paper, three series of ethynyl‐extended regioisomers of 2‐(2′‐hydroxyphenyl)benzothiazole (HBT), at the 3′‐, 4′‐ and 6‐positions, respectively, have been synthesized. Changes in the absorption and emission spectra were correlated with the position and electronic nature of the substituent groups. Although 4′‐ and 6‐substituted HBT derivatives exhibited absorption bands at longer wavelengths, the keto‐emission of 3′‐substituted HBT derivatives was found at a substantially longer wavelength. The gradual red‐shifted fluorescence emission was found for 3′‐substituted HBT derivatives where the electron‐donating nature of substituent group increased, which was opposite to what was observed for 4′‐ and 6‐substituted HBT derivatives. The results derived from the theoretical calculations were in conformity with the experimental observations. Our study could potentially provide experimental and theoretical basis for designing novel ESIPT dyes that possess unique fluorescent properties.     

Description of the Structure and Properties of Atactic Polystyrene Melt Using Integral Equation Theory

The polymer reference interaction site model （PRISM） integral equation theory was used to describe the structure and thermodynamic properties of atactic polystyrene （aPS） melt, in which the monomer of aPS is represented with an eight-site model to characterize its microstructure. The intramolecular structure factors needed in the PRISM calculations were obtained from single chain MD simulations. The calculated results indicate that the results by the integral equation method agrees well with experiments, and can reflect the fine microscopic structure of real aPS melt. This work shows that the PRISM theory is a powerful tool for investigating the structure and properties of complex polymers.     

Synthesis and characteristics of the mass spectra of 2,5-dimercapto-2,5-dimethyltetrahydrothiophene

2,5-Dimercapto-2,5-dimethyltetrahyrothiophene was synthesized by the reaction of 1-iodopropan-2-one with hydrogen sulfide in an ether solution of hydrogen chloride at-70°C. Its structure was established by mass spectrometry, ¹H and ¹³C NMR spectroscopy. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, 216–219, February, 2007.     

New organogermanium cations [RGe(OCH2CH2NME2)2]+ with intramolecular N→Ge coordination bonds

New organohalogermanes RGe(OCH₂CH₂NMe₂)₂X (R = Ph, X = I (5); R = Me, X = Cl (6) or I (7)) with an intramolecular N→Ge coordination bond were synthesized. According to the ¹H and ¹³C NMR spectroscopic data, iodides 5 and 7 exist in solution as ionic compounds with the pentacoordinated germanium atom. In solution of compound 4 (R = Ph, X = Cl), there is an equilibrium between the ionic and covalent forms. The equilibrium shifts toward the ionic form with increasing solvent polarity or temperature. In solution, chloride 6 is a covalent compound. The structures and relative stabilities of different isomers of compounds 4–7 were studied by quantum chemical calculations at the density functional level of theory. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 892–900, May, 2007.     

Synthesis and Structure of a 1,3-alternate-Thiacalix[4]arene diamide Derivative

A novel receptor possessing two complexation sites and bearing 1,3-alternate conformation based on thiacalix[4]arene, confirmed by single crystal X-ray analysis, was prepared. The tetrathiacalix[4]arene diamide shows strong intramolecular hydrogen bonding. The binding behavior towards K⁺ and halides has been examined by ¹H NMR titration experiments.     

On the mechanism of proton transfer in imidazole

The force fields, in-plane vibrations, and relative intensities of Raman spectra have been calculated and analyzed for the N₁H and N₃H tautomers of imidazole, imidazolium cation, and their model structures. The results obtained for the isolated state of imidazole correspond to the intramolecular mechanism of proton transfer.     

Effects of Halogen Substitution on Naphthazarin Tautomerism in the Ground and Excited States

5,8-Hihydroxyl-1,4-naphthazarin was taken as a model compound to explore the effect of halogen substitution on intramolecular proton transfer process. Calculations indicate that the substitution in the R2- and R4-positions far away from the active region has much weaker influence on the IPT process than that in the R1-and R3-positions. IPT barriers for substitution in the R1-position are higher than that of parent molecule. However, it is quite reverse for substitution in the R3-position. The IPT process is a proton transfer process coupled with charge separation and coulombic interaction would be dominant during this process. As for naphthazarin, halogen substitution would decrease the quantum yields of O2 but increase those of 1O2.     

From anisole to 1,2,4,5‐tetramethoxybenzene: Theoretical study of the factors that determine the conformation of methoxy groups on a benzene ring

Unhindered ortho‐dimethoxy‐substituted phenyl rings often display a coplanar conformation. A theoretical study of a series of methoxybenzenes consisting of methoxybenzene (anisole), the three dimethoxybenzenes, and 1,2,4,5‐tetramethoxybenzene, at the DFT/B3LYP/6‐311++G** level of theory, allows us to identify the factors influencing the conformational preference and attribute the coplanarity of such methoxy groups to mesomeric effects. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

An approach to estimate the energy and strength of the intramolecular hydrogen bond in different conformers of 4‐methylamino‐3‐penten‐2‐one

The molecular structure and intramolecular hydrogen bond energy of 32 conformers of 4‐methylamino‐3‐penten‐2‐one were investigated at MP2 and B3LYP levels of theory using the standard 6–31G** basis set and AIM analyses. Furthermore, calculations for all the possible conformations of 4‐methylamino‐3‐penten‐2‐one in water solution were also carried out at B3LYP/6–31G** level of theory. The calculated geometrical parameters and conformational analyses in gas phase and water solution show that the ketoamine conformers of this compound are more stable than the other conformers (i.e., enolimine and ketoimine). This stability is mainly due to the formation of a strong N? H···O intramolecular hydrogen bond, which is assisted by π‐electrons resonance. Hydrogen bond energies for all conformers of 4‐methylamino‐3‐penten‐2‐one were obtained from the related rotamers method. The nature of intramolecular hydrogen bond existing within 4‐methylamino‐3‐penten‐2‐one has been investigated by means of the Bader theory of atoms in molecules, which is based on topological properties of the electron density. The results of these calculations support the results which obtained by related rotamers method. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

A high-pressure mass spectrometric and density functional theory investigation of the thermochemical properties and structure of protonated dimers and trimers of glycine

A new modification of pulsed-ionization high-pressure mass spectrometry (PHPMS) has been used to perform equilibrium thermochemical studies for relatively nonvolatile biomolecules such as amino acids. Binding enthalpy and entropy changes have been measured for proton-bound clusters of glycine, which are in good agreement with both theoretical (DFT) results of this work and a previous blackbody infrared dissociation experiment. Experimental data indicate that a number of conformers of the proton-bound dimer of glycine may coexist in the explored temperature range (360-460 K). Several new, conceptually different isomers (two of them zwitterionic) have been found by DFT calculations, one of which is 7 kJ mol(-1) lower in energy than the structure previously reported to be the energy minimum.