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The synthesis and characterization of neutral heteroleptic molecular iridium(III) complexes with (2,4-difluoro)phenylpyridine and different pyridine-1,2,4-triazole ligands are described. The studies have shown high external quantum efficiencies and color points better than the standard for blue iridium(III) bis[(4,6-difluorophenyl)pyridinato-N,[C.sup.2]]picolinate.

A comparison of rate constants measured for an intervalence (IV) compounds with electron-transfer parameters obtained from its optical absorption spectrum is done using resonance Raman analysis. It is suggested that the Zhu-Nakamura preexponential factor provides good consistency for the ESR rate constants using a value, averaged single-mode which closer to those predicted from the resonance Raman spectroscopic data but need slightly higher electronic coupling than [V.sub.Hush].

Photochemical charge separation within aromatic hydrazines and the effect of exited-state intervalence in dihydrazines are studied. The results suggest that the most noticeable consequence of the exited-state intervalence is, under 60% as large for Hy2(super 14)NA compared to Hy(super 1)NA and for a significantly smaller Strokes shift for the distributed compared to the monosubstituted compounds Hy2(super 26)NA compared to Hy(super 2)NA.

Analysis of optical spectra of a pseudo-para-dinitro[2.2]paracyclophane radical anion using Marcus-Hush theory reveals that its off diagonal coupling element, Hab, is large enough, relative to its reorganization energy, to change from a localized class II compound to a delocalized class II compound by changing solvents.

A model for the quantitative treatment of dihydrazine diradical dication, which possesses mixed valence excited states is introduced and utilized for explaining the observed spectroscopic consequences. Results indicate that the excited-state mixed valence could play an important role in the electronic spectra of many organic and inorganic compounds.

The electron transfer (ET) in four symmetrically substituted naphthalene-bridged bis-hydrazine radical cations is compared within the Marcus-Hush framework. The results show that ET rates estimated for four naphthalene bridged bis-hydrazine radical cations vary significantly and show no correlation with the distance between the charge-bearing units.

The optical spectrum of 2,7-dinitronaphthalene radical anion generated by Na(Hg) reduction in acetonitrile containing a large excess of cryptand[2.2.2] exhibits a Hush-type intervalence charge-transfer band at 1070nm, estimated to correspond to an off-diagonal matrix coupling element. Intramolecular electron transfer rate constants are predicted within an order of magnitude by a Marcus-Hush-type two-state classical model analysis of the optical spectrum.

Research has been conducted on intervalence radical anions which demonstrate charge-transfer bands in their near-IR spectra. The authors discuss the absorption bands of delocalized dinitroaromatic anions with aromatic bridges, and compare their optically derived electron transfer parameters with those of radical anions.

The optical spectrum of 2,7-dinitronaphthalene radical anion generated by Na(Hg) reduction in acetonitrile containing a large excess of cryptand[2.2.2] exhibits a Hush-type intervalence charge-transfer band at 1070 nm, estimated to correspond to an off-diagonal matrix coupling element of 310 cm-1. The interpolated rate constant for intramolecular electron transfer at 293 K measured by ESR between 225 and 320 K for this solution is 3.1(±.2) x 109 s-1. Rate constants estimated in two ways from the optical parameters using the Marcus-Hush assumption that the diabatic surfaces should be parabolae are 1.0 and 0.11 x 109 s-1, and those using diabatic surfaces that fit the observed charge-transfer band are 9.6 and 3.4 x 109 s-1, when used with an electron-transfer distance on the adiabatic surfaces of 6.42 Å. Similar measurements and comparisons were also carried out using dimethylformamide and butyronitrile as solvents. The success of simple, classical two-state Marcus-Hush theory precludes an electron-hopping mechanism. UHF calculations predict a planar unsymmetrical gas-phase structure for 1 ,3-dinitrobenzene radical anion but give serious spin contamination. Semiempirical AM1 calculations using singles excitation configuration interaction with an active space of 70 orbitals and the COSMO solvent model also give a planar unsymmetrical structure. These calculations make the internal vibrational component of the reorganization energy nearly constant, and much smaller than the solvent reorganizational component, and predict the transition energy to lie between that observed in acetonitrile (9360 cm-1) and those observed in dimethylformamide (8100 cm-1) and butyronitrile (8040 cm-1). [ABSTRACT FROM AUTHOR]

Tetraazaperopyrene and a range of derivatives have been synthesised and their photophysical and redox-chemical properties studied. The parent compound, 1,3,8,10-tetraazaperopyrene (1), was prepared by treating 4,9-diamino-3,10-perylenequinone diimine with triethyl orthoformate, whereas the 2,9-disubstituted derivatives of 1 were obtained after treatment with the corresponding carboxylic acid chloride or anhydride (2 mol equiv). The 1,3,8,10-tetraazaperopyrene core structure was established by X-ray diffraction of 2,9-bis(2-bromophenyl)-1,3,8,10-tetraazaperopyrene (6). The UV-visible absorption spectra of the compounds have a characteristic visible pi(*)<--pi absorption band at 440 nm (log epsilon(max)=4.80) with a strong vibrational progression (Delta nu approximately 1450 cm(-1)). Diprotonation of the nitrogen atoms induces a bathochromic shift of this band from 430-440 to 470-480 nm and all four nitrogen atoms are protonated when pure H(2)SO(4) is used as the solvent. The first and second as well as the third and fourth protonations occur concomitantly, which implies that they have very similar pK(a) values and, consequently, similar proton affinities. A theoretical study of the proton affinities in the gas phase and in solution attributes this behaviour to the effects of polar solvents, which dampen the charge of a protonated site at the other end of the molecule and thus effectively decouple the two opposite pyrimidine units in the polycondensed aromatic compound. The photophysical data were modelled in a time-dependent DFT study of 1, 1H(2)(2+) and 1H(4)(4+) in both the gas phase and in a polar solvent. All the dyes show weak fluorescence in organic solvents, however, their protonated conjugate acids show dramatically increased fluorescence intensity. All of the dyes undergo two electrochemically reversible one-electron reductions with cyclovoltammetric half-wave potentials at E(red1) approximately -0.9 V and E(red2) approximately -1.3 V (vs. SCE), which are associated with characteristic spectral changes.

Analysis of optical spectra of a pseudo-para-dinitro[2.2]paracyclophane radical anion using Marcus-Hush theory reveals that its off diagonal coupling element, H(ab), is large enough, relative to its reorganization energy, to change it from a localized class II compound to a delocalized class III compound by changing solvents. The optical spectra, along with frontier orbital analysis, show that the assumption that E(op) = 2H(ab) for class III compounds is not true in this case.

[structure: see text] The optical diffuse reflectance and solution spectra of two bis-hydrazine radical cationic intervalence compounds have been compared. The results are consistent with an ion-pairing increase and an "effective polarity" in these crystals that is not far from that of acetonitrile or other polar solvents.