Synthesis and Electrochemistry of Novel Dumbbell-Shaped Bis-pyrazolino[60]fullerene Derivatives Formed Using Microwave Radiation

The design of covalently linked [60]fullerene dimers has gained increased attention, as the linked electron donors or acceptors are in close proximity to the surface of the C60, providing a valuable approach to novel molecular electronic devices. Herein, new compounds involving C60 dumbbells covalently connected by the π-conjugated system from azobenzene and diaryl ether linkers were synthesized following the bifunctional cycloaddition reactions to C60 using microwave radiation. The structural identity of the fullerene dimers has been determined using spectroscopic techniques including Fourier transform infrared (FT-IR), matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF), and NMR spectroscopy, and the photophysical and the electrochemical properties for the new dumbbells have been examined using UV-vis spectroscopy, fluorescence spectroscopy, cyclic voltammetry, and square wave voltammetry. Both new dimers show electronic interaction with the fullerene cage and higher electron affinity than the pristine C60.

Synthesis and Electrochemistry of New Furylpyrazolino[60]fullerene Derivatives by Efficient Microwave Radiation

Efficient one-pot synthesis of new series of furylpyrazolino[60]fullerene derivatives was prepared by [3 + 2] cycloaddition reaction mediated with (diacetoxyiodo)benzene (PhI(OAc)₂) as an oxidant in o-dichlorobenzene (ODCB) under microwave irradiation. Different techniques have been used to confirm the structural identity including FT-IR, fast atom bombardment (FAB)-mass, NMR, and single-crystal X-ray diffraction, in addition to investigating the photophysical properties and the electrochemical properties for the new compounds using UV-Vis spectra, fluorescence spectra, cyclic voltammetry, and square wave voltammetry. Three of these pyrazolino[60]fullerene compounds showed better electron affinity than the parent C₆₀ in the ground state.

Donor-Donor'-Acceptor Triads Based on [3.3]Paracyclophane with a 1,4-Dithiafulvene Donor and a Cyanomethylene Acceptor: Synthesis, Structure, and Electrochemical and Photophysical Properties

Donor-donor'-acceptor triads (1, 2), based on [3.3]paracyclophane ([3.3]PCP) as a bridge, with electron-donating properties (D') using 1,4-dithiafulvene (DTF; TTF half unit) as a donor and dicyanomethylene (DCM; TCNE half unit) or an ethoxycarbonyl-cyanomethylene (ECM) as an acceptor were designed and synthesized. The pulse radiolysis study of 1 a in 1,2-dichloroethane allowed the clear assignment of the absorption bands of the DTF radical cation (1 a^.+ ), whereas the absorption bands due to the DCM radical anion could not be observed by γ-ray radiolysis in 2-methyltetrahydrofuran rigid glass at 77 K. Electrochemical oxidation of 1 a first generates the DTF radical cation (1 a^.+ ), the absorption bands of which are in agreement with those observed by a pulse radiolysis study, followed by dication (1 a²⁺ ). The ESR spectrum of 1 a^.+ showed a symmetrical signal with fine structure and an ESR simulation predicted that the spin of 1 a^.+ is delocalized over S and C atoms of the DTF moiety and the central C atom of the trimethylene bridge bearing the DTF moiety. Pulse radiolysis, ESR, and electrochemical studies indicate that the DTF radical cation of 1 a^.+ is more stable than that of 6^.+ , and the latter shows a strong tendency to dimerize. This result indicates that the [3.3]PCP moiety as a bridge can stabilize the DTF radical cation more than the 1,3-diphenylpropane moiety because of kinetic stability due to its rigid structure and the weak electronic interaction of DTF and DCM moieties through [3.3]PCP.

CHAMELEON GROUND STATE AND EXCITED STATES OF EDT-TTF-IM-F4TCNQ RADICAL DYAD IN DIFFERENT ENVIRONMENTS

We have performed a systematic density functional study on the ground-state electronic structure and excited states of a representative D-σ-A dyad, i.e. EDT-TTF-Im-F4TCNQ π-radical, in vacuo and in different conventional solvents (toluene, THF, DMF and DMSO) by using some popular hybrid density functionals (B3LYP, M05, M05-2X, PBE0 and BMK). It has been shown that the M05 and B3LYP functionals perform the best in predicting the intramolecular charge-transfer (ICT) pertaining to both the ground state and excited states of the dyad. The amphoteric dyad is liable to solvent-promoted ICT from its EDT-TTF-Im donor (D) to F4TCNQ acceptor (A), adopting a charge-unseparated ground state D-A• in vacuo, a partially zwitterionic ground state [D-A]• in nonpolar toluene solvent, and a fully zwitterionic ground state D•+-A- in such polar solvents as THF, DMF and DMSO. Owing to its solvent-dependent chameleon ground state, excited states of the dyad in solvents also exhibit remarkable dependence on solvent polarity, as revealed by TDDFT calculations. Furthermore, cluster model calculations revealed that intermolecular charge-transfer readily occurs between the dyads, accounting for the observed zwitterionic charge state in solid state and solid-state semiconductivity.

Tetrathiafulvalene vinylogues as versatile building blocks for new organic materials

Although tetrathiafulvalene (TTF) and its derivatives have been extensively studied as important organic electronic materials over the past half century, tetrathiafulvalene vinyl-ogues (TTFVs) still remain a relatively underdeveloped branch in the family of TTF derivatives. Our recent work has investigated the synthesis and characterization of a class of diphenyl-substituted TTFVs carrying alkynyl functionality. The unique conformational and redox properties of such TTFV derivatives along with the versatile chemistry enabled by acetylenic groups (e.g., metal-catalyzed coupling and click reactions) have led us to a variety of functional molecular architectures ranging from oligoynes, polymers, and molecular tweezers, to macrocycles. Property studies of these new TTFV-based molecular materials point to appealing applications in molecular electronics and optoelectronics.