Synthesis,X-Ray Crystallography,Theoretical Investigation and Optical Properties of 2-Chloro-N-(2,4-dinitrophenyl) Acetamide

Journal of Chemical Crystallography - 2-Chloro-N-(2,4-dinitrophenyl) acetamide, 1, was synthesized and characterized by 1H and 13C NMR spectroscopy, ESI–MS, X-ray crystallography, and...     

Effects of the CN and NH2 substitutions on the geometrical and optical properties of model vinylfluorenes,based on DFT calculations

A systematic study on the structural and photo-physical properties of model bifluorenevinylene compounds based on the density functional theory (DFT) and its time-dependent (TD-DFT) version is presented. The main aim of this work is to investigate the influence of substitution on bifluorenevinylene using strong electron acceptor CN or electron donor NH₂ groups on: (a) the optimal geometry, (b) torsional potentials and (c) photo-physical properties. Our results indicate that the substitution on the vinylene bridge, leads to the twisting of molecular fragment on the side of added group and are in good overall agreement with experiment. In the case of the amino mono-substituted bifluorenevinylene, the amino group leads to non-planarity at the non-substituted portion of the molecule. The chemical modification also have a pronounced impact on the electronic properties. The shape of the potential energy curves evaluated for the lowest vertically excited states is heavily dependent on the molecular conformation. Finally, we discuss how the structural and electronic information presented here can be useful in designing of novel optical materials as well as understanding of excitation–relaxation phenomena which may occur in various time-dependent optical experiments.     

Understanding on absorption and fluorescence electronic transitions of carbazole-based conducting polymers: TD-DFT approaches

The electronic excitation transitions of carbazole-based oligomers, (Cz-co-Cz) _N , (Cz-co-Fl) _N and (Cz-co-Th) _N (N = 2–4) were investigated using density functional theory (DFT) and time-dependent (TD) DFT methods. Our results show that the calculated ground state geometries favor a more aromatic, planer structure, while the electronically excited geometries favor a quinoidic type structure. Absorption and fluorescence energies have been obtained from TD-B3LYP/SVP calculations performed on the S₁ optimized geometries and are in excellent agreement with experimental data. The experimental fluorescence excitation energies for (Cz-co-Cz)₄, (Cz-co-Fl)₄ and (Cz-co-Th)₄ (2.76, 2.63, and 2.25 eV, respectively) correspond closely with the predicted S₁ transitions (2.84, 3.91 and 2.43 eV, respectively). We also report the predicted radiative lifetimes 0.52, 0.47, and 0.99 ns for (Cz-co-Cz) _N , (Cz-co-Fl) _N and (Cz-co-Th) _N , discuss the origin of the small stoke shift of the carbazole based oligomers and the magnitude of bathochromic shifts. We conclude by discussing the benefits of theoretical calculations, which can provide critical structural and electronic understanding of excitation–relaxation phenomena that can be exploited in design of novel optical materials.     

The effect of alkali and Ce(III) ions on the response properties of benzoxazine supramolecules prepared via molecular assembly

A series of benzoxazine monomer supramolecules with different substituted groups on their benzene ring was prepared with a Mannich reaction and characterized by FTIR, 1H-NMR and MS. The obtained products were 3,4-dihydro-3-(2'-hydroxyethylene)-6-methyl-2H-benzoxazine (BM1), 3,4-dihydro-3-(2'-hydroxyethylene)-6-ethyl-2H-benz-oxazine (BM2), and 3,4-dihydro-3-(2'-hydroxyethylene)-6-methoxy-2H-benzoxazine (BM3). The efficiency of alkali metal ion extraction from the products was determined with Pedersen's technique, while the complexation of the Ce(III) ion was confirmed by the Job's and the mole ratio methods. The evidence of complex formation between benzoxazine monomers and Ce(III) ions was obtained with FTIR and a computational simulation. Single phase ceria (CeO?) as observed with XRD was successfully prepared by calcinating the Ce(III)-benzoxazine monomer complexes at 600 °C for 2 h. In addition, the geometry of the ceria nanoparticles confirmed by TEM is spherical, with an average diameter of 10-20 nm.     

Photophysical properties and photochemistry of EE-, EZ-, and ZZ-1,4-dimethoxy-2,5-bis[2-(thien-2-yl)ethenyl] benzene in solution: theory and experiment

Photophysical properties and photoisomerization of 1,4-dimethoxy-2,5-bis[2-(thien-2-yl)ethenyl] benzene (DMTB) have been investigated for the EE-, EZ-, and ZZ- stereoisomers. The EE-DMTB was prepared, and the absorption/fluorescence spectra of EE- isomer as well as transient spectra in photoisomerization among three isomers were observed. Absorption and fluorescence spectra of three isomers were analyzed by the symmetry-adapted cluster-configuration interaction (SAC-CI) and time-dependent density functional theory (TDDFT) methods. The characteristics of the absorption spectra of three isomers were satisfactorily reproduced by the direct SAC-CI and TDDFT methods in both peak position and intensity. The relative stability of three isomers and the photoisomerization among these isomers were also examined theoretically. The ground (S(0)) and first excited state (S(1)) geometries were calculated by the DFT/TDDFT method with the M06HF functional, and the calculated S(0) structures of EE- and ZZ- isomers agreed well with those of the X-ray structures. The geometry relaxation in the S(1) state was interpreted with regard to the excitation character. The solvent effect in the absorption and fluorescence spectra was examined by the polarizable continuum model (PCM) and was found to be 0.05-0.20 eV, reflecting the charge polarization. The results show that the photophysical properties of DMTB can be controlled with the conformation constraint and also indicate the possibility of a photofunctional molecular device such as a switching function.