Synthesis and characterization of N-alkyl 1,3-diamino-4,6-diamidobenzenes

A new preparation of N-substituted 1,3-diamino-4,6-diamidobenzenes has been achieved. This synthesis affords the first N-alkylamino derivatives for which a fine-tuning of the NR¹R² substituents should modify the reactivity of the amine functions.     

Photoinduced energy transfer and charge transfer on squarylium cyanine dyes

A series of squarylium cyanine dyes (Sqs) were synthesized to explore their applications in functional devices.Preliminary investigation on the mechanism involved in these devices was carried out.Spectroscopic behavior of Sqs with porphyrin (P),8-hydroxyquinolium aluminum (Alq) and ruthenium bipyridyl complex (Ru(bipy)) in solution,in film and on nanocrystalline TiO2 was investigated,respectively.A mechanism including photoinduced energy transfer and charge transfer processes was suggested in the corresponding practical devices.By means of doping,a red organic electroluminescent device (ELD) using Sq-doped Alq as the emission layer (EML) has been developed,and the total light to electricity efficiency of nanocrystalline TiO2 electrode based on using Sq-doped Ru(bipy) as photosensitizer has been improved greatly in the whole visible region,particularly in the red area above 600 nm.     

Protonation of 1,3- and 1,4-dinitrobenzene dianions

The protonation of the electrochemically generated (0.1 M solution of tetrabutylammonium perchlorate in DMF) 1,3-dinitrobenzene (1) dianions with phenol, ethanol, tert-butanol, and 1-butyl-3-methylimidazolium cation was studied by cyclic voltammetry and chronoamperometry at the carbositall working electrode. The rate constants for the protonation (k) of the dianion of compound 1 by phenol, 1-butyl-3-methylimidazolium cation, ethanol, and tert-butanol were estimated by the comparison of the data of cyclic voltammetry and chronoamperometry with the digital simulation results, being 100, 50, 1.5, and 0.01 L mol⁻¹ s⁻¹, respectively. The similarly obtained k value for the protonation of the dianion of 1,4-dinitrobenzene (2) with phenol is 13 L mol⁻¹ s⁻¹. According to the quantum chemical calculation results, the protonation of the dianions of compounds 1 and 2 with phenol and 1-butyl-3-methylimidazolium cation can be classified as orbital-controlled reactions. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1463–1466, July, 2008.     

Optical charge transfer transitions in supramolecular fullerene and porphyrin compounds

By the DFT method with the planar wave basis set and in the PAW approximation the geometric and electronic structures of four supramolecular compounds of porphyrin and fullerene molecules in the crystalline state are performed: H₂TPP·C₆₀·3 toluene, H₂T_pivPP·C₆₀, H₂T_3,5-dimethylPP·C₇₀·4 toluene, and NiT_4-methylPP·2C₇₀·2 toluene. The geometry is optimized using the PBE functional and the Grimme DFT-D2 dispersion interaction correction. The electronic structure and absorbance spectra are calculated using the HSE functional. It is shown that the H₂TPP·C₆₀·3 toluene structure having a sufficiently wide absorbance wavelength range, which results in a photoinduced electron transition from the higher occupied states formed by porphyrin molecules to the lower unoccupied states formed by fullerene molecules, is most promising for the design of photogalvanic elements.     

Solid-state fluorescence of squarylium dyes

An N-butyl indolenine squarylium dye could include toluene and p-xylene and exhibited the solid-state fluorescence in near-infrared region (F_max=761 nm) in crystalline form due to inhibition of π/π-interactions between the fluorophores.     

Solid-state phase transitions of polytetrafluoroethylene crystals studied with an ultra-high-pressure ac calorimeter

The solid-state phase transitions of polytetrafluoroethylene crystals have been studied with an ultra-high-pressure ac calorimeter developed in the authors’ laboratory. The temperature dependence of heat capacity has been measured at various pressures from 0.1 to 580 MPa. It was found that excess heat capacity had long tails around the phase transition temperatures. A phase diagram was drawn and compared with reported one. In the high-temperature phase called phase I, the boundary of different phases was confirmed in this work.     

Synthesis and spectral characteristics of two novel intramolecular charge transfer fluorescent dyes

The synthesis and absorption/fluorescence properties of two novel intramolecular charge transfer (ICT) compounds of (fluorene-2-yl)-(9-ethylcarbazole-3-yl) ketene and 1-phenyl-3-(fluorenone-2-yl)-5-(9-ethylcarbazole-3-yl)-2-pyrazoline were reported. The primary structure of the target compounds was characterized by IR and ¹H NMR. The systems contained a fluorenone or a propenon group as an electron acceptor (A) and an N-ethylcarbazole and a pyrazoline group as electron donors (D). From the emissive properties it was concluded that the electronic coupling between D and A was sufficient to allow charge transfer in these molecules. The ICT maximal emission displayed a large wavelength shift and Stokes shifts increased in response to the increase of the solvent polarity. The highly solvatochromic properties made the two compounds of great interest as new classes of fluorescent probes, electroluminescent and electrofax materials.     

Double proton transfer and charge transfer transitions in hydrogen-bonded systems: formic acid dimer

The barriers for double proton transfer in the ground and lowest Π-Π^* and Π-Π^* excited states of the formic acid dimer have been calculated within a modified INDO scheme. Analysis of the nature of the excited electronic states, with emphasis on charge-transfer transitions, has been performed. The results indicate a lower barrier in the excited Π-Π^* states than in the ground state.     

Aqueous polymeric sensors based on temperature-induced polymer phase transitions and solvatochromic dyes

This feature article provides, for the first time, an overview of the research that guided the way from fundamental studies of the thermo-responsive phase separation of aqueous polymer solutions to polymeric sensor systems. The incorporation of solvatochromic dyes into thermoresponsive polymers as well as the concepts of polymeric sensors are presented and discussed in detail.     

Synthesis and properties of 4,6-diamino-3-cyano-2(1H)-pyridineselenone: Molecular and crystal structure of 2-allylseleno-4,6-diamino-3-cyanopyridine

Self-condensation of cyanoselenoacetamide gives 4,6-diamino-3-cyano-2(1H)pyridineselenone, which is regioselectively alkylated at the exocyclic heteroatom. The cisoid position of the Se-C bonds of the selenoallyl substituent relative to the N-C bond of the pyridine ring in the N¹C²SeC⁸ fragment favors cyclization into selenazolo[3,2-a]pyridinium salts.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2585–2590, November, 1989.     

Ligand-metal overlap as source of intensity for ligand field and charge transfer transitions

Experimental evidence for a strong decrease of intensities in both ligand field and charge transfer spectra with increased metal-ligand distance is presented. It suggests that overlap of charge clouds for metal ion and ligands is a major source of their intensities. The polarization ratios in noncubic crystals also appear to be largely determined by differences in bond lengths. Data from the literature are consistent with this interpretation. Potential applications of this still tentative principle for the gathering of structural information on pure and doped crystals as well as on amorphous systems are discussed.     

Pseudo-stark splitting of charge transfer transitions of KCrO3Cl

A linear pseudo Stark splitting has been observed for the 5476 and 5379A?sharp line origins found in the spectrum of KCrO₃Cl. The effect is large (2.5 and 3.2 cm^?1 for 10⁵ V/cm) and promises to be an important new probe in the study of charge transfer transitions.     

Furo- and thieno-fused 1,3-diazepine-4,6-diones

We report the first preparation of furo- and thieno-fused 1,3-diazepine-4,6-dione derivatives starting from ethyl 2-(2-methoxy-2-oxoethyl)-3-furancarboxylate and -thiophencarboxylate. The ester functionalities connected to the hetero-ring were converted regiospecifically into the desired amides. The ester groups attached to the methylene unit were converted into isocyanates via Curtius rearrangement. The ring-closure reaction was performed in the presence of lithium bis(trimethylsilyl)amide at room temperature to give furo- and thieno-fused diazepinone derivatives.     

Combining high electron affinity and intramolecular charge transfer in 1,3-dithiole-nitrofluorene push-pull diads

Attaching electron-rich 1,3-dithiol-2-ylidene moieties to polynitrofluorene electron acceptors leads to the formation of highly conjugated compounds 6 to 11, which combine high electron affinity with a pronounced intramolecular charge transfer (ICT) that is manifested as an intense absorption band in their visible spectra. Such a rare combination of optical and electronic properties is beneficial for several applications in optoelectronics. Thus, incorporation of fluorene-dithiole derivative 6a into photoconductive films affords photothermoplastic storage media with dramatically increased photosensitivity in the ICT region. A wide structural variation of the dithiole and fluorene parts of the molecules reveals excellent correlation between the ICT energy and the reduction potential with the Hammett's parameters for the substituents. Although only a small solvatochromism of the ICT band was observed, heating the solution led to a pronounced blueshift, which was probably as a result of increased twisting around the C9=C14 bond that links the fluorene and dithiole moieties. X-ray crystallographic analysis of 7a, 8a, 10a, 11a and 13a confirms an ICT interaction in the ground state of the molecules. The C9=C14 double bond between the donor and acceptor is substantially elongated and its length increases as the donor character of the dithiole moiety is enhanced.     

Structure of the 1,3-dinitrobenzene dianion studied by multiconfigurational methods

The structure of the 1,3-dinitrobenzene dianion in the ground and lowest excited electron states was studied by quantum chemical methods. The dianion, unlike the radical anion, is characterized by the symmetrical structure in both the ground triplet (³B₁) and lowest excited singlet (¹A₁) states. The wave function of the singlet state has the biradical character to a great extent. The singlet-triplet splitting calculated by the CASSCF and MRMP2 methods is 6 and 2 kcal mol⁻¹, respectively. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1408–1410, July, 2007.