Tetracyanoethylene Acceptor Research Articles

Utilization of tannic acid into spherical structured carbons based on charge-transfer complexation with tetracyanoethylene acceptor: Liquid-liquid and solid-solid interactions

In this study, liquid-liquid and solid-solid interactions between tannic acid (TA) as a donor with tetracyanoethylene (TCNE) acceptor were investigated toward understanding the effect of starting material phase on the end product of a charge transfer (CT) reaction. The liquid-liquid interaction generated a reddish-brown, soluble CT complex, while the solid-solid interaction produced a deep-violet, solid CT complex. The stoichiometry of the interaction was obtained using an elemental analysis of the solid product and spectrophotometric titration and Job's method for the soluble product and these data both indicated a 1:5 (TA:TCNE) molar ratio. The UV–visible and IR measurements support the presence of π-π interactions between the TA donor and TCNE acceptor. The two CT complexes obtained from the two interactions were directly carbonized into particles. These resultant carbon particles were fully characterized using IR, XRD, SEM, and TEM. These analyses revealed that carbon particles with spherical morphology were obtained after the carbonization of the CT complex generated through the solid-solid interaction, while the liquid-liquid interaction led to carbon particles with semi-porous, irregular morphology.

Charge-transfer excitations in molecular donor-acceptor complexes within the many-body Bethe-Salpeter approach

We study within the perturbative many-body GW (Green’s function G and the screened Coulomb interaction W) and Bethe-Salpeter approach the low lying singlet charge-transfer excitations in molecular donor-acceptor complexes associating benzene, naphthalene, and anthracene derivatives with the tetracyanoethylene acceptor. Our calculations demonstrate that such techniques can reproduce the experimental data with a mean average error of 0.1-0.15 eV for the present set of dimers, in excellent agreement with the best time-dependent density functional studies with optimized range-separated functionals. The present results pave the way to the study of photoinduced charge transfer processes in photovoltaic devices with a parameter-free ab initio approach showing equivalent accuracy for finite and extended systems.

Reliable Prediction of Charge Transfer Excitations in Molecular Complexes Using Time-Dependent Density Functional Theory

We show how charge transfer excitations at molecular complexes can be calculated quantitatively using time-dependent density functional theory. Predictive power is obtained from range-separated hybrid functionals using nonempirical tuning of the range-splitting parameter. Excellent performance of this approach is obtained for a series of complexes composed of various aromatic donors and the tetracyanoethylene acceptor, paving the way to systematic nonempirical quantitative studies of charge-transfer excitations in real systems.

Mulliken–Hush elucidation of the encounter (precursor) complex in intermolecular electron transfer via self-exchange of tetracyanoethylene anion-radical

The paramagnetic [1:1] encounter complex ( TCNE ) 2 - is established as the important precursor in the kinetics and mechanism of electron-transfer for the self-exchange between tetracyanoethylene acceptor ( TCNE) and its radical-anion as the donor. Spectroscopic observation of the dimeric complex ( TCNE ) 2 - by its intervalence absorption band at the solvent-dependent wavelength of λ IV ∼ 1500 nm facilitates the application of Mulliken–Hush theory which reveals the significant electronic interaction extant between the pair of cofacial TCNE moieties with the sizable coupling of H DA = 1000 cm −1. The transient existence of such an encounter complex provides the critical link in the electron-transfer kinetics by lowering the classical Marcus reorganization barrier by the amount of H DA in this strongly adiabatic system. Ab initio quantum-mechanical methods as applied to independent theoretical computations of both the reorganization energy ( λ) and the electronic coupling element ( H DA) confirm the essential correctness of the Mulliken–Hush formalism for fast electron transfer via strongly coupled donor/acceptor encounter complexes.

Molecular adducts between a few phenolic donors and π-acceptors in solid-state

Electron donor–acceptor molecular complexes of a few phenolic donors with some quinonoid and tetracyanoethylene acceptors have been prepared by two different methods, i.e., by simple grinding of the respective component pair in the solid-state and in solution. Both the methods yielded identical dark colored 1:1 stoichiometric complexes. Spectral studies revealed that the complexes are ionic in nature. The g values obtained in ESR spectral studies for all these molecular adducts vary between 2.000 and 2.022, confirming the free radical nature of the adducts. The electronic absorption spectral studies proved that the donor–acceptor complexes formed initially, exhibit new electronic transitions at longer wavelengths, are less stable and disassociate readily into ionic type of adducts. The absorption maximum at longer wavelengths, i.e. ≥550 nm, are assigned to the charge transfer complexes, while the new transition at around 410 ± 5 nm is attributed to the anion radical of the adducts. The ease of complexation not only depends on the ionization potential and electron affinities of the phenolic donors and the acceptors but is also structure sensitive. Complexation is confirmed by the shift in IR absorption of the phenolic hydroxyl group and the carbonyl group of quinone acceptors and the cyano group of tetracyanoethylene. Proton magnetic resonance studies indicate an interaction between the phenolic donors and acceptors on basis of the altered chemical shifts. Further, IR and NMR studies show that the stability of the adducts is governed not only by the charge transfer interaction but also by hydrogen bonding.

Donor−Acceptor Complexes of Alkylcarbazole and Dicarbazolylalkane Donors with the Acceptors Tetracyanoethylene and Tetranitromethane

Electron donor−acceptor complexes of conformationally flexible 1,n-dicarbazolylalkanes (C12H8N−(CH2)n−NC12H8), where n = 1−5, were examined. Carbazole, methylcarbazole, ethylcarbazole, and cyanoethylcarbazole also were studied as monochromophoric analogues for comparison. In dichloromethane solution, the dicarbazolylalkanes form 1:1 complexes with the terminal carbazolyl chromophores acting as independent donors when n ≥ 2. With the acceptor tetranitromethane (TNM), the carbazoles form contact complexes displaying small positive enthalpies of formation. In contrast, stable complexes form with the acceptor tetracyanoethylene (TCNE). Crystalline TCNE complexes were isolated for the bichromophoric donors with n = 2−4. The solid complexes and their uncomplexed donor components were analyzed by single-crystal X-ray diffraction. The solid-state stoichiometries of (carbazolyl donor):(TCNE acceptor) were found to depend on the donor conformation. Dicarbazolylalkane donors separated by two or four methylene units ...

Resonance Raman Intensity Analysis of the Carbazole/Tetracyanoethylene Charge-Transfer Complex: Mode-Specific Reorganization Energies for a Hole-Transport Molecule

A resonance Raman intensity analysis is presented for the carbazole/tetracyanoethylene donor−acceptor charge-transfer complex in dichloromethane solution. The intent is to determine the nuclear reorganization contributions to the rates of charge hopping in carbazole polymers used as hole-transport agents in the xerographic (electrophotographic) process. Resonance Raman cross sections have been measured at seven excitation wavelengths spanning the broad visible charge-transfer absorption known to consist of two strongly overlapping charge-transfer electronic transitions. Interference between the Raman amplitudes from these two transitions manifests itself in the Raman excitation profiles for a number of resonantly enhanced modes. Simultaneous modeling of the absorption spectrum and the Raman cross sections shows that explicit consideration of the signs as well as the magnitudes of the normal mode displacements is required to reproduce the experimental data. The signs of the mode displacements obtained from the modeling are shown to be consistent with qualitative predictions based on the nodal patterns of the donor molecular orbitals and the forms of the resonantly enhanced normal modes. Mode-specific reorganization energies for the carbazole donor and tetracyanoethylene acceptor are obtained from the analysis along with parameters describing the magnitude and time scale of the solvent contributions to the reorganization energy. Approximately 60% of the total reorganization energy of 5100 cm-1 in each charge-transfer state is attributed to solvent and any other classically behaved low-frequency modes, with the remainder about equally divided between donor and acceptor modes. The partitioning of the reorganization energy among the carbazole modes is significantly different for the two electronic transitions.

Noncovalent synthesis of donor/acceptor stacks

Supramolecular arrays composed of alternating tetracyanoethylene acceptors (A) and 1,4-dioxybenzene-based donors (D) self-assemble spontaneously in the solid state. Infinite one-dimensional […A…D…A…D…] stacks are formed by co-crystallizing tetracyanoethylene and 1,4-dimethoxybenzene. When bis- p-phenylene-34-crown-10, possessing two 1,4-dioxybenzene donors (D-D) bridged by polyether chains, is employed, infinite one-dimensional […A…D-D…A…D-D…] arrays are formed with the cavities of macrocyclic polyethers of adjacent stacks perfectly in register to afford channels — occupied by MeCN molecules — along one crystallographic direction.