Formation of conjugated polynaphthalene via Bergman cyclization

A series of enediyne containing chiral phthalimides were synthesized through Sonogashira coupling reactions. These enediynes were then subjected to thermal Bergman cyclization under vacuum. Polynaphthalenes with pendant chiral groups were obtained and characterized using GPC, IR spectroscopy, NMR spectroscopy, UV–Vis spectroscopy, and photoluminescence analysis. Under properly optimized conditions, the chirality of chiral directing group was maintained according to CD spectra of final products. After removal of chiral directing groups, weak CD signals representative of main chain chirality were visible. Further modification of the structure of the enediyne compounds will facilitate the synthesis of chiral polynaphthalene through this rather simple way. Extension of the Bergman cyclization to polymer chemistry is promising in the construction of novel polymers with rigid polyarene backbones. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2187–2193, 2010     

Theoretical studies on the electronic structures and absorption spectra of substituted benzenes with one- and two-dimensional charge transfer character

The electronic structures and absorption spectra of one- and two-dimensional charge transfer (CT) molecules based on para-nitroaniline (pNA) and 1,3-diamino-4,6-dinitro- benzene (DADB) have been studied theoretically via semi-empirical and ab initio methods. It is found that the behaviors of optical absorption are strongly influenced by the dimension of CT. Different from the well-known one-dimensional CT molecule of pNA, which shows one intense absorption related to the π → π^* CT transition, two-dimensional CT molecule of DADB exhibits more absorption peaks associated with various low-lying CT transitions in near ultraviolet range. In addition, the relative orientations of transition dipole moment and ground state dipole moment in one- and two-dimensional charge transfer molecules were also discussed.     

Trends in Conjugated Chalcogenophenes: A Theoretical Study

Heavy atom substitution in chalcogenophenes is a versatile strategy for tailoring and ultimately improving conjugated polymer properties. While thiophene monomers are commonly implemented in polymer designs, relatively little is known regarding the molecular properties of the heavier chalcogenophenes. Herein, we use density functional theory (DFT) calculations to examine how group 16 heteroatoms, including the radioactive polonium, affect polychalcogenophene properties including bond length, chain twisting, aromaticity, and optical properties. Heavier chalcogenophenes are more quinoidal in character and consequently have reduced band gaps and larger degrees of planarity. We consider both the neutral and radical cationic species. Upon p-type doping, bond length rearrangement is indicative of a more delocalized electronic structure, which combined with optical calculations is consistent with the polaron-model of charge storage on conjugated polymer chains. A better understanding of the properties of these materials at their molecular levels will inevitably be useful in material design as the polymer community continues to explore more main group containing polymers to tackle issues in electronic devices.     

Theoretical and experimental studies on the performances of barbital‐imprinted systems

By using density functional theory, we studied the interaction process between barbital and 2‐vinyl‐4,6‐diamino‐1,3,5‐triazine in acetonitrile at 333 K. Barbital and 2‐vinyl‐4,6‐diamino‐1,3,5‐triazine were used as the template and functional monomer, respectively. The molecularly imprinted polymer microspheres containing barbital and 2‐vinyl‐4,6‐diamino‐1,3,5‐triazine were synthesized through precipitation polymerization. After removing the template molecule barbital, the average diameter of the obtained molecularly imprinted polymers was 1.45 μm. By optimizing the molar ratio of barbital and the 2‐vinyl‐4,6‐diamino‐1,3,5‐triazine, the resulting molecularly imprinted polymers showed the highest adsorption for the barbital. The analysis of the Scatchard plot revealed that the dissociation constant (K_d) and apparent maximum adsorption quantity (Q_max) of the molecularly imprinted polymers were 30.69 mg/L and 8.68 mg/g, respectively. The study of selective adsorption showed that molecularly imprinted polymers exhibited higher selectivity for barbtital than that for 1,3‐dimethyl barbituric acid and pentobarbital. Herein, the studies can provide theoretical and experimental references for the barbital‐imprinted system.     

Theoretical study on the structures and electronic spectra of TCNE2-.

Investigations into the charge-separated states and electron-transfer transitions in tetracyanoethylene (TCNE) complexes have recently generated much interest. In this work we present theoretical calculations showing that the most stable structure of the dianion TCNE2- has D2d symmetry in vacuum as well as in the solvents dichloromethane and acetonitrile. By means of the coupled cluster linear response, we compute the vertical electronic spectrum in both the gas phase and solution. The theoretical results are compared to the experimental data and good agreement is achieved.     

Oxidation potential of thiophene oligomers: Theoretical and experimental approach

Intrinsic properties of conducting polymers, such as oxidation potential and band gap, are very important for designing new materials with improved properties. Computational chemistry offers suitable tools capable of predicting these quantities. This work presents electrochemical information about accurate oxidation potentials of oligothiophenes and polymer band gap. These are compared to theoretical predictions based on electronic structure calculations at Density Functional Theory levels, coupled with self‐consistent reaction field. All computational protocols gave a qualitative prediction of the experimental trend. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Theoretical studies on the structures and electronic spectra of C75B−

Intermediate neglect of differential overlap (INDO) calculations were used to study the structure of C₇₅B^?—the isoelectronic molecule of C₇₆. It was found that the boron atom mainly substitutes the second carbon atom (there are 19 types of carbon atoms in C₇₆). The electronic spectra of all the possible isomers of C₇₅B^? were calculated based on the optimized geometries. It was shown that the UV‐Vis spectra of C₇₅B^? and C₇₆ resemble each other in many ways with the exception of the absorptions beyond 700 nm. The red shift of the absorptions was rationalized and nature of transition of the peaks discussed. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003     

Raman Spectra of Poly(p‐phenylenevinylene)s with Fluorinated Vinylene Units: Evidence of Inter‐ring Distortion

Ring the changes : Experimental Raman spectra of fluorinated and non‐fluorinated polyphenylenevinylenes are assigned according to quantum chemical calculations for oligomer model systems (see picture). Characteristic differences in the spectra can be traced back to strong inter‐ring distortion of the fluorinated compounds.

     

Theoretical studies on absorption, emission, and resonance Raman spectra of Coumarin 343 isomers

The vibrationally resolved spectral method and quantum chemical calculations are employed to reveal the structural and spectral properties of Coumarin 343 (C343), an ideal candidate for organic dye photosensitizers, in vacuum and solution. The results manifest that the ground-state energies are dominantly determined by different placements of hydrogen atom in carboxylic group of C343 conformations. Compared to those in vacuum, the electronic absorption spectra in methanol solvent show a hyperchromic property together with the redshift and blueshift for the neutral C343 isomers and their deprotonated anions, respectively. From the absorption, emission, and resonance Raman spectra, it is found that the maximal absorption and emission come from low-frequency modes whereas the high-frequency modes have high Raman activities. The detailed spectra are further analyzed for the identification of the conformers and understanding the potential charge transfer mechanism in their photovoltaic applications.     

Theoretical and experimental studies of cationized uracil complexes in the gas phase

Cationized uracil clusters were generated in the gas phase by electrospray ionization (ESI). Mass spectrometry experiments showed that with particular experimental conditions, decameric uracil clusters are magic number clusters. MS/MS experiments demonstrated that the structure of these decameric uracil clusters depends substantially on the size and the charge of the cation. On the basis of the ab initio and density functional theory (DFT) quantum chemistry calculations, structures for these decameric clusters were proposed. These structures are in agreement with the experimental mass spectra of modified nucleobases. Theoretical calculations showed that complexes experimentally observed using ESI-MS techniques, are not naturally the most stable in the gas phase.     

Comparison of ground and excited state polarizabilities of thiophene,cyclopentadiene, and fulvene oligomers and their cyano substituted derivatives—Ab initio study

Ab Initio study of the ground and excited state polarizabilities of thiophene, fulvene, and cyclopentadiene based conducting oligomers and their cyano derivatives have been performed using the restricted Hartree–Fock (RHF) and the configuration interaction singles (CIS) approaches, respectively, with 3‐21G* basis set. For comparison purposes, for some small oligomers (monomers and dimers), higher basis sets (6‐31G*, 6‐31+G*, aug‐cc‐pVTZ) were also employed in the computations of polarizabilities. The trends in polarizability as a function of oligomer length were investigated. For all systems, the RHF polarizability increases as n^1.2–1.3 as n gets larger and the CIS polarizability increases as n^1.4–1.6 for n less than seven or eight rings and then increases approximately linearly with n for larger n. For the thiophene based systems the dependence of the polarizability on bond length alternation (BLA) along the backbone of the oligomers was also investigated using the RHF, density functional (DFT), and CIS theories (with 3‐21G* basis set). For thiophene dimer, we also performed RHF/aug‐cc‐pVTZ calculations of polarizabilities versus BLA. We found that the polarizability is largest when BLA is near zero (for both ground and excited states), which correlates with the lowest excitation energy. Comparison with experimental results has been made where possible. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1983–1995, 2007     

Theoretical Designs of Molecular Photonics Materials

Different theoretical models for the computation of multiphoton absorption response are described and reviewed. The influences of intrinsic molecular structure parameters on the multiphoton absorption properties for organic conjugated molecules are discussed in terms of: i) the donor/acceptor substitutions; ii) the π conjugation length; iii) the ground‐state polarization mimicking structural character such as bond‐length alternation; iv) the molecular dimensionality; and, v) some other possible factors, such as vibronic coupling and the solvent, as well as aggregation effects. Some theoretical designing strategies for organic materials with large multiphoton cross‐sections are then proposed.

     

DFT and experimental studies of the structure and vibrational spectra of curcumin

The potential energy surface of curcumin [1,7‐bis(4‐hydroxy‐3‐methoxyphenyl)‐1,6‐heptadiene‐3,5‐dione] was explored with the DFT correlation functional B3LYP method using 6‐311G* basis. The single‐point calculations were performed at levels up to B3LYP/6‐311++G**//B3LYP/6‐311G*. All isomers were located and relative energies determined. According to the calculation the planar enol form is more stable than the nonplanar diketo form. The results of the optimized molecular structure are presented and compared with the experimental X‐ray diffraction. In addition, harmonic vibrational frequencies of the molecule were evaluated theoretically using B3LYP density functional methods. The computed vibrational frequencies were used to determine the types of molecular motions associated with each of the experimental bands observed. Our vibrational data show that in both the solid state and in all studied solutions curcumin exists in the enol form. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Theoretical DFT and experimental Raman and NMR studies on thiophene, 3-methylthiophene and selenophene

The results of extended MO calculations using density functional theory (DFT) approximation supported by experimental Raman, ¹H and ¹³C NMR studies on thiophene are reported. Raman spectra of liquid thiophene were re-examined and the performance of a hybrid B3PW91 density functional was compared with the ab initio restricted Hartree–Fock (RHF) method. With the basis sets of the 6-311++G^** quality, the DFT calculated bond lengths, dipole moments and harmonic vibrations were predicted in a very good agreement with available experimental data.

Additionally, the results on thiophene were extended by calculations on 3-methylthiophene and selenophene. In this case, a significant change in geometry and charge distribution in thiophene ring due to a methyl group substituent or replacement of sulphur by selene atom was observed.

A linear correlation between the predicted harmonic vibrational frequencies (scaled using SQM method) and experimental ones for thiophene, selenophene and 3-methylthiophene was shown. The theoretically calculated spectra have satisfactorily reproduced the available experimental spectra for thiophene and selenophene.     

Raman and photoacoustic infrared spectra of fluorene derivatives: Experiment and calculations

Raman and photoacoustic (PA) infrared spectra of fluorene and four derivatives (2,3-benzofluorene, 2-methylfluorene, 2-ethylfluorene and 1,8-dimethylfluorene) were recorded and analyzed in this investigation. Mid- and far-infrared PA spectra were examined from about 2000 to 100 cm⁻¹. The Raman spectra spanned the same wavenumber range. Observed bands in both PA and Raman spectra were compared with DFT (harmonic) and variational (anharmonic) calculations, and with published spectra. The DFT calculations provided single-molecule frequencies, whereas the variational method yielded results for both monomeric and dimeric species. Many previously unknown bands, including numerous features due to combination and overtone transitions, were identified and assigned in this work.     

Long-wave Raman spectra of some normal alcohols

Long-wave Raman spectra of some normal alcohols (from n-pentanol to n-decanol) in the liquid phase were registered. The regularities in the dependencies of Raman bands frequencies on the number of carbon atoms in the hydrocarbon chain were deduced. The calculations of Raman spectra of the studied molecules, their equilibrium structures and possible conformers were carried out in the approximation B3LYP/cc-pVDZ. These results in combination with the analysis of literature data allowed to explain the observed regularities in Raman band positions in the spectral range of 200–600 сm⁻¹ and their shifts upon increasing length of the chains. It was found that the plane configurations dominate in the liquid phase for molecules with short- and moderate-chain lengths. The elongation of the chain leads to the decrease of the fraction of plane conformers and in n-decanol the plane structure is completely absent.     

Synthesis and optoelectronic properties of conjugated polymers based on a dithienobenzimidazole unit in the main chain

Three conjugated polymers with the dithienobenzimidazole (DTBIm) unit ( P1 , P3 , and P4 ) and one conjugated polymer with the dithienobenzoxazole unit ( P2 ) were synthesized by the cross‐coupling polymerization. The absorption maxima showed a red‐shift in the order of P3 (406 nm), P2 (426 nm), P1 (438 nm), and P4 (450 nm), which was studied in detail using the frontier molecular orbital calculation of the model compounds. The energy levels of the highest occupied molecular orbital and the lowest unoccupied molecular orbital of the DTBIm unit‐containing conjugated polymers were estimated by the cyclic voltammetry. The transformation from DTBIm ( P4 ) to dithienobenzimidazolium ( P4' ) was also carried out to shift the absorption maxima of P4' (454 nm) by promoting the intramolecular charge transfer between the DTBIm and thiophene units. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 401–409     

Synthesis and electroluminescent studies of blue‐emitting copolymers containing phenylene vinylene and oxadiazole moieties in the main chain

Two statistical copolymers III and IV combining features of the two reference polymers I and II were synthesized by a Wittig reaction with the objective of raising the electron‐transport properties and fluorescence quantum yields relative to the alternating block copolymers I and II . The electroluminescent properties of single‐layer LEDs using these copolymers were studied. External quantum efficiencies of 0.035 and 0.11% were obtained from single‐layer devices on the basis of III and IV , respectively, which are higher than those of similar devices using I and II . Two single‐layer LEDs using a blend of I and II (4:1 and 1:1 wt/wt) corresponding to the compositions of copolymers III and IV , respectively, were also fabricated for comparison. Results indicated that the covalent incorporation of oxadiazole is effective in improving the efficiency of LEDs and that the molar content of oxadiazole plays an important role in the performance of the devices. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 235–241, 2002     

Theoretical studies on the S-N interactions in sulfoximine

The potential energy surface of sulfoximines has been searched using ab initio MO and Density Functional Calculations. The electronic structures of the isomers of sulfoximine have been studied using HF/6-31+G*, MP2(full)/6-31+G* and B3LYP/6-31+G* levels. Final energies of these molecules have been calculated at the high accuracy G2 and CBS-Q levels. Though a formal SN double bond is generally considered between sulfur and nitrogen in these systems, theoretical studies do not show any π interaction between them. S-N rotational barriers, bond dissociation energies, atomic charge analysis, and NBO analysis all indicate only a single bond across S-N with a very strong ionic interaction.     

Theoretical studies on the structures and vibrational spectra of Ni, Pd, and Pt phthalocyanines

Electronic structure calculations and spectroscopic assignments for metallophthalocyanines NiPc, PdPc and PtPc are performed on optimized geometries at B3LYP/LANL2DZ level. The order of the sizes of the central hole is computed to be PdPc > PtPc > NiPc, with the hole size of PdPc close to that of PtPc. The Mulliken charges of the central M vary in the order of PtPc > NiPc > PdPc, and the HOMO-LUMO gaps are in the order of NiPc < PdPc < PtPc, in agreement with the experimental result. The simulated IR spectra for the three derivatives are compared with the experimental absorption spectra, and very good consistency has been obtained. The simulated medium intensity bands associated with the metal-ligand vibrations which appear as singlet bands at 880, 877 and 883 cm⁻¹, respectively, exhibit the order of PtPc > NiPc > PdPc, which is the same order as experiment. Furthermore, the metal-ligand vibrational bands for Raman spectra shift in the order NiPc > PtPc > PdPc. The strongest Raman lines predicted at 1562, 1532 and 1534 cm⁻¹ for NiPc, PdPc and PtPc are very sensitive to the metal ion.