A series of monodisperse Et3-Si-end-capped poly(triacetylene) (PTA) oligomers ranging from monomer to hexadecamer was prepared by a fast and efficient statistical deprotection-oxidative Hay oligomerization protocol. The PTA oligomers exhibit an increasingly deep-yellow color with lengthening of the pi-conjugated backbone, feature excellent solubility in aprotic solvents, and exhibit melting points up to > 22 degrees C for the hexadecameric rod. This new dramatically extended oligo(enediyne) series now enables to investigate the evolution of the physico-chemical effects in PTAs beyond the linear 1/n versus property regime into the higher oligomer region where saturation becomes apparent. We report the results of joint experimental and theoretical studies, including analysis of the 13C NMR spectra, evaluation of the linear (UV/ Vis) and nonlinear [third-harmonic generation (THG) and degenerate four-wave mixing (DFWM)] optical properties, and characterization of the redox properties with cyclic and steady-state voltammetry. Up to the hexadecameric rod, an increasingly facile one-electron reduction step is observed, showing at the stage of the dodecamer, a leveling off tendency from the linear correlation between the inverse number of monomer units and the first reduction potential. The effective conjugation length (ECL) determined by means of UV/Vis spectroscopy revealed a pi-electron-delocalization length of about n = 10 monomeric units, which corroborates well with the oligomeric length for which in the 13C NMR spectrum C(sp2) and C(sp) resonances start to overlap. Third-harmonic generation (THG) and degenerate four-wave mixing (DFWM) measurements revealed for the second-order hyperpolarizability gamma a power law increase gammma-alpha-n(a) for oligomers up to the octamer with exponential factors a= 2.46+/-0.10 and a=2.64+/-0.20, respectively, followed by a smooth saturation around n = 10 repeating units. The power law coefficient a calculated with the help of the valence effective Hamiltonian (VEH) method combined to a sum-over-states (SOS) formalism corroborates well with the values found by both THG and DFWM experiments. Up to the PTA heptamer, INDO (intermediate neglect of differential overlap)-calculated gas-phase ionization potentials and electron affinities obey a linear relationship as a function of the inverse number of monomer units displaying a strong electron-hole symmetry. The onset of saturation for the electron affinity is calculated to occur around the octamer, in accordance with experimentally obtained results from electrochemical measurements.

A series of diverse binuclear and mononuclear cyclometalated palladium(ii) complexes of different structure was investigated by electrochemical techniques combined with density functional theory (DFT) calculations. The studies including cyclic and differential pulse voltammetry, X-ray structure analysis and quantum chemical calculations revealed a regularity of the complexes oxidation potential on the metal-metal distance in the complexes: the larger Pd-Pd distance, the higher oxidation potentials. The reduction potentials feature unusually high negative values while no correlation depending on the structure could be observed. These results are in a good agreement with the electron density distribution in the complexes. Additionally, ESR data obtained for the complexes upon oxidation is reported.

Poly(triacetylenes) are rodlike molecules with electrons delocalized over a one-dimensional path. We show that they exhibit a power-law dependence of the second-order hyperpolarizability gamma on the monomer unit n for short molecules and a smooth saturation toward a linear increase in longer molecules. The power law of gamma?n(a) with a approximately 2.5 from dengenerate four-wave mixing and third-harmonic generation measurements is in good agreement with quantum-chemical calculations. The critical conjugation length for saturation in the three cases is shown to be approximately 60 carbon-carbon bonds, which indicates the upper boundary for the electron delocalization in such a one-dimensional molecular wire.

Quantum chemical modeling in combination with vibrational and electronic absorption spectroscopy has delivered detailed information about supramolecular organization of azochromophore 4-amino-4′-nitroazobenzene (DO3), its solutions, and blends with poly(methyl methacrylate) (PMMA) polymer of various concentrations. It is shown that the neat chromophore contains both antistacked forms and hydrogen bonded associations of the "head-to-tail" type, while separate DO3 molecules dominate in diluted solutions of DO3 in chloroform. In PMMA/DO3 films with low concentrations of the chromophore, DO3 is mainly Hbonded to CO moieties of PMMA matrix, while in the blends with high concentrations of DO3 molecules, the latter form hydrogen bonds both with PMMA and with each other. Infrared, Raman, and UV−vis spectroscopic markers of isolated DO3 molecules and various modes of their supramolecular associations are revealed.

ABSTRACT:In this paper the effect of solvents of different polarity (chloroform and acetone) on the geometry and static electric properties (dipole moment, polarizability, and first hyperpolarizability) of four nonlinear optical (NLO) chromophores is studied within the framework of the Polarizable Continuum Model (PCM) at the Self-consistent Field (SCF) level. The standard 6-31G** basis set is used for the chromophore geometry optimization both in the gas phase and in the solvents, and a moderate-size aug-cc-pVDZ* basis set is used for the calculation of electric properties of the chromophores under study. The effect of the solvent on the geometrical parameters of the chromophores is shown to be insignificant. However, to avoid inaccuracies in estimation of first hyperpolarizability, the use of chromophore geometries, optimized in a solvent, is recommended for chromophores with a rather long conjugation bridge between electron-donating and electron-withdrawing groups. The solvent effect on the calculated values of first hyperpolarizability results in its strong enhancement by a factor of 2.9 -2.3 in the case of chloroform and by a factor of 3.9 -2.8 in the case of acetone, the effect being somewhat attenuated with the lengthening of the conjugation bridge in the series of chromophores.

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Here, the synthesis, characterization, and photovoltaic properties of four new donor-acceptor copolymers are reported. These copolymers are based on 4,4-difl uoro-cyclopenta[2,1-b:3,4-b′] dithiophene as an acceptor unit and various donor moieties: 4,4-dialkyl derivatives of 4H-cyclopenta[2,1-b:3,4-b′]dithiophene and its silicon analog, dithieno[3,2-b:2′,3′-d]-silol. These copolymers have an almost identical bandgap of 1.7 eV and have a HOMO energy level that varies from −5.34 to −5.73 eV. DSC and X-ray diffraction (XRD) investigations reveal that linear octyl substituents promote the formation of ordered layered structures, while branched 2-ethylhexyl substituents lead to amorphous materials. Polymer solar cells based on these copolymers as donor and PC 61 BM as acceptor components yield a power conversion effi ciency of 2.4%.

Structure and nonlinear optical properties of small clusters formed of organic chromophores through H-bonding are studied by the example of dimer and trimer of p-nitroaniline (PNA). The analysis of the electron charge density pattern in the bonding region in terms of "Atoms in Molecules" approach is performed, and the values of electron charge density, Laplacian of electron density at critical points, etc. are determined. Topological analysis has given evidence of the existence of three-center interaction of one amino group hydrogen with oxygens of nitro group of the neighboring PNA, resulting in two H-bond formation. Solvent effect on the static (hyper)polarizability of the clusters is studied by the example of PNA dimer in acetone in the framework of conventional Polarizable Continuum Model as well as supermolecule and semicontinuum approaches. The essential increase of the cluster hyperpolarizability in comparison with that of a single chromophore is obtained. The account of specific interaction with the solvent molecule is shown to result in moderate or significant enhancement of ␤ ʈ depending on the structure of the formed cluster.