Linear oligoarylamines: electrochemical, EPR, and computational studies of their oxidative states.

A series of straight-chain oligoarylamines were synthesized and examined by electrochemical, spectroelectrochemical, electron paramagnetic resonance techniques, and density functional theory (DFT) calculation. Depending on their electrochemical characteristics, these oligoarylamines were classified into two groups: one containing an odd number and the other an even number of redox centers. In the systems with odd redox centers (N1, N3, and N5), each oxidation was associated with the loss of one electron. As for the systems with even redox centers (N2, N4, and N6), oxidation occurred by taking N2 as a unit. Absorption spectra of linear oligoarylamines at various oxidative states were obtained to investigate their charge transfer behaviors. Moreover, DFT-computed isotropic hyperfine coupling constants and spin density were in accordance with the EPR experiment, and gave a close examination of oligoarylamines at charged states.

Studies on the structure of N-phenyl-substituted hexaaza[1(6)]paracyclophane: synthesis, electrochemical properties, and theoretical calculation.

The N-phenyl-substituted hexaaza[1(6)]paracyclophane (3, hexamer) has been synthesized successfully in two steps and the noncoplanar conformation was calculated by gaussian program. The electrochemical properties exhibited lots of interesting results and each overlapping oxidative wave contained two-electron transfer.

Intriguing electrochemical behavior of free base porphyrins: effect of porphyrin-meso-phenyl interaction controlled by position of substituents on meso-phenyls.

Electrochemical properties of substituted free base meso-tetraphenylporphyrins (H(2)T(o,o'-X)PP, H(2)T(o-X)PP, and H(2)T(p-X)PP, where X = OCH(3), CH(3), H, F, or Cl on the phenyl rings) are examined by cyclic voltammetry. When a substituent is located only at the para position of the meso-phenyl group, the difference between the first and second oxidation potentials (ΔE(ox), i.e., E(2)(ox) - E(1)(ox)), is generally significantly smaller than those of the H(2)TPPs with bulky o,o'-substituents on the phenyl group. This trend is elucidated with density functional theory calculations and attributed mainly to the sterically controlled π-conjugation of the meso-phenyl groups to the central porphyrin ring, rather than the often discussed deformation of porphyrin.

Electron transfer and binding affinities in an electrochemically controlled ligand transfer system containing zinc porphyrin and a meso-phenylenediamine substituent.

Investigations on the transfer of the ligand, imidazole (HIm), between two covalently linked redox centres--zinc porphyrin and phenylenediamine (PD)--and the influence of the length of the linker are reported. Since the binding affinity of the ligand with zinc porphyrin is different from that of the ligand with the phenylenediamine moiety, the transfer of the ligand could be electrochemically controlled by adjusting the oxidation potentials. Changes in cyclic voltammograms and absorption spectra of the complexes revealed the site of ligand binding in the various oxidation states of the modified zinc porphyrins. Binding constants of the modified zinc porphyrins in various oxidation states were also determined by photometric titration with the ligand and digital simulations. Evidence for the delocalization of the electron from the zinc porphyrin to the phenylenediamine moiety and the influence of the delocalization on them were obtained from EPR studies.

Electrochemically controlled multiple hydrogen bonding between triarylamines and imidazoles.

By increasing the number of amino substituents on triarylamine, the extent of hydrogen bonding between the oxidized form of triarylamine and imidazole could be electrochemically controlled. Three behaviors, depending on the interaction between oxidized amine and imidazole, were obtained in CV patterns. DFT calculation was used to confirm that the electron density of protons of the amino group decreased as the amino moiety increased.

Excited state luminescence of multi-(5-phenyl-1,3,4-oxadiazo-2-yl)benzenes in an electron-donating matrix: exciplex or electroplex?

Multi-(5-phenyl-1,3,4-oxadiazo-2-yl)benzenes show emission in organic solvents from ultraviolet to blue (339-447 nm). The reduction potentials E(1/2)(red) cover a large range of -2.11 V for 2,5-diphenyl-1,3,4-oxadiazole to -0.76 V for 1,2,3,4,5,6-hexa(5-phenyl-1,3,4-oxadiazo-2-yl)benzene. An unexpectedly wide spectral range of the oxadiazole (OXD) exciplex emissions in PVK is observed, ranging from 406 to 603 nm. The OXDs also exhibit similar electroluminescence (EL) when blended into polyvinylcarbazole (PVK). A linear correlation between the lambda(max) of the electroluminescence and photoluminescence is observed, implying that the emission mechanisms in both processes are similar. In addition, the linear correlation between the E(1/2)(red) versus lambda(max) of EL (eV) reflected that the term of the charge-transfer configuration of the contact electron-hole pair plays a major role in the exciplex emission. The exciplex EL of 1,2,5-tri(5-phenyl-1,3,4-oxadiazo-2-yl)benzene (5) could be as high as 1.0 cd/A. Since the exciplex emission usually has a large Stokes shift, this provides a window for us to generate duo emissions for near white light EL with high efficiency. Among the devices we tried, the device of PVK/2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole/5/2,5,8,11-tetra-tert-butylperylene (100:40:40:4) gave EL with good current efficiency of 1.63 cd/A.