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Abstract: The one-electron oxidation potential of 10 triarylamines 1–10 with all permutations of chloro-, methoxy- and methyl-substituents in the three para-positions were determined by cyclic voltammetry. The half wave potential E 1/2(I) of the first oxidation wave correlates linearly with the number of chloro- and methoxy-substituents. A high long-term stability of the first oxidation wave for all triarylamines was observed by multi-cycle thin-layer measurements. AM1-CISD derived values of the absorption energies are in good agreement with the experiments but differ strongly for the oscillator strengths as well as for neutral compounds 1–10 and their corresponding mono radical cations. The small solvent dependence of the experimental UV/Vis spectra in CH2Cl2 and MeCN reflects a minor charge transfer (CT) character of the electronic transitions of neutral and cationic compounds. [Copyright &y& Elsevier]

The excited state absorption spectra of biphenyl and 2,5-dimethyl biphenyl have been investigated by femtosecond broad band pump–probe spectroscopy in organic solvents. The results show vastly different intensities that were analyzed by calculating transition density surfaces for characteristic S1→Sn absorptions. The analysis revealed strong symmetry-lowering substituent effects in 2,5-dimethyl biphenyl which directly affect the transition dipole moments for excited state absorption. By measuring the temporal evolution of the transient spectra of the biphenyl derivatives we observed a biphasic relaxation mechanism in the excited state characterized by two distinct time scales of 400 fs and 12 ps. [Copyright &y& Elsevier]

We have investigated three organic mixed-valence systems that possess nearly identical inter-redox site distances and differ by the nature of the bridging units benzene, naphthalene, and anthracene: the N,N,N',N'-tetra(4-methoxyphenyl)-1,4-phenylenene-diamine radical cation (1+), the 1,4-bis(N,N-di(4-methoxyphenyl)-amino)naphthalene radical cation (2+), and the 9,10-bis(N,N-di(4-methoxyphenyl)amino)-anthracene radical cation (3+). The electronic interactions in these systems have been studied by means of gas-phase ultraviolet photoelectron spectroscopy, vis/NIR spectroscopy, and electronic-structure calculations. The experimental and theoretical results concur to indicate that the strength of electronic interaction decreases in the following order of bridging units: benzene > naphthalene > anthracene. This finding contradicts the usual expectation that anthracene is superior to benzene as a driving force for electronic communication. We explain these results in terms of a super-exchange mechanism and its strong dependence on steric interactions. [ABSTRACT FROM AUTHOR]

The electronic and molecular structure of N,N,N',N'-tetraphenylphenylenediamine radical cation 1+ is in focus of this study. Resonance Raman experiments showed that at least eight vibrational modes are strongly coupled to the optical charge resonance band which is seen in the NIR. With the help of a DFT-based vibrational analysis, these eight modes were assigned to symmetric vibrations. The contribution of these symmetric modes to the total vibrational reorganization energy is dominant. These findings are in agreement with the conclusions from a simple two-state two-mode Marcus-Hush analysis which yields a tiny electron-transfer barrier. The excellent agreement of the X-ray crystal structure analysis and the DFT computed molecular structure of 1+ on one hand as well as the solvent and solid-state IR spectra and the DFT-calculated IR active vibrations on the other hand prove 1+ adopts a symmetrical delocalized Robin-Day class III structure both in the solid state and in solution. [ABSTRACT FROM AUTHOR]