Synthesis, spectroscopic properties, and photoconductivity of black absorbers consisting of pt(bipyridine)(dithiolate) charge transfer complexes in the presence and absence of nitrofluorenone acceptors.

The diimine-dithiolato ambipolar complexes Pt(dbbpy)(tdt) and Pt(dmecb)(bdt) (dbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine; tdt(2-) = 3,4-toluenedithiolate; dmecb = 4,4'-dimethoxyester-2,2'-bipyridine; bdt(2-) = benzene-1,2-dithiolate) are prepared herein. Pt(dmecb)(bdt) exhibits photoconductivity that remains constant (photocurrent density of 1.6 mA/cm(2) from a 20 nm thin film) across the entire visible region of the solar spectrum in a Schottky diode device structure. Pt(dbbpy)(tdt) acts as donor when combined with the strong nitrofluorenone acceptors 2,7-dinitro-9-fluorenone (DNF), 2,4,7-trinitro-9-fluorenone (TRNF), or 2,4,5,7-tetranitro-9-fluorenone (TENF). Supramolecular charge transfer stacks form and exhibit various donor-acceptor stacking patterns. The crystalline solids are "black absorbers" that exhibit continuous absorptions spanning the entire visible region and significant ultraviolet and near-infrared wavelengths, the latter including long wavelengths that the donor or acceptor molecules alone do not absorb. Absorption spectra reveal the persistence of donor-acceptor interactions in solution, as characterized by low-energy donor/acceptor charge transfer (DACT) bands. Crystal structures show closely packed stacks with distances that underscore intermolecular DACT. (1)H NMR provides further evidence of DACT, as manifested by upfield shifts of aromatic protons in the binary adducts versus their free components, whereas 2D nuclear Overhauser effect spectroscopy (NOESY) spectra suggest coupling between dithiolate donor protons with nitrofluorenone acceptor protons, in correlation with the solid-state stacking. The NMR spectra also show significant peak broadening, indicating some paramagnetism verified by magnetic susceptibility data. Solid-state absorption spectra reveal further red shifts and increased relative intensities of DACT bands for the solid adducts vs solution, suggesting cooperativity of the DACT phenomenon in the solid state, as further substantiated by νC-O and νN-O IR bands and solid-state tight-binding computational analysis.

Brightly phosphorescent tetranuclear copper(i) pyrazolates.

Described herein is the synthesis and photophysics of two tetranuclear copper complexes, {[3,5-(Pri)2,4-(Br)Pz]Cu}4 and {[3-(CF3),5-(But)Pz]Cu}4 tailor-designed by manipulating the pyrazolyl ring substituents. Unlike their trinuclear analogues, the luminescence of the tetranuclear species is molecular (not supramolecular) in nature with extremely high solid-state quantum yields of ∼80% at room temperature.

Structural, magnetic, and optoelectronic properties of (diimine)(dithiolato)platinum(II) and -palladium(II) complexes and their charge-transfer adducts with nitrile acceptors.

Two new diimine dithiolato complexes, (dbbpy)Pt(dmid), 1, and (dbbpy)Pd(dmid), 2, were prepared and characterized (dbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine; dmid = 2-oxo-1,3-dithiole-4,5-dithiolate). Both complexes interact with the nitrile acceptor TCNQ, and 1 also interacts with TCNQF(4) and TCNE (TCNQ = 7,7,8,8-tetracyanoquinodimethane; TCNQF(4) = 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane; TCNE = tetracyanoethylene) to form supramolecular 2:1 charge-transfer solids that stack in the manner -DDADDADDA- (D = electron donor; A = electron acceptor). All compounds have been fully characterized by magnetic, spectroscopic, electrochemical, and single-crystal X-ray crystallographic analyses. Magnetic susceptibility studies of the charge-transfer compounds revealed that the platinum-based complexes exhibit temperature-independent paramagnetism of approximately 10(-3) emu/mol. The donor complexes exhibit continuous absorption bands across the UV/visible and into the NIR region. Upon interaction with the nitrile acceptors, the extinction coefficients of the absorption bands increase and the energies of some d-d transitions in the NIR region change. The donor-acceptor compounds possess desired spectral features for solar cell dyes, but low conversion efficiencies resulted when a representative compound was tested in a TiO(2) solar cell. The results, however, serve to illustrate that the donor-acceptor interactions persist in solution and the adsorption of the dye molecules to the semiconductor surface occurs in the absence of typical anchoring groups. Evaluation of the spectral and electrochemical data for the title compounds and the results of the preliminary solar cell study serve as guides for future research in choosing promising candidates for efficient solar cell dyes.