Two series of Pt(diimine)(dithiolate) complexes have been prepared in order to investigate the effects of molecular design on the excited-state properties of this chromophore. The first series comprises Pt(dbbpy)(dithiolate) complexes where dbbpy ) 4,4′-di-tert-butyl-2,2′-bipyridine and the dithiolates are 1-(tert-butylcarboxy)-1-cyanoethylene-2,2-dithiolate (tbcda), 1-diethylphosphonate-1-cyanoethylene-2,2-dithiolate (cpdt), 6,7-dimethylquinoxaline-2,3-dithiolate (dmqdt), maleonitriledithiolate (mnt), and toluene-3,4-dithiolate (tdt). The second series comprises Pt(diimine)(tdt) complexes where the diimines are 3,4,7,8-tetramethyl-1,10-phenanthroline (tmphen), 4,4′-di-tert-butyl-2,2′-bipyridine (dbbpy), 4,4′-dimethyl-2,2′-bipyridine (dmbpy), 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), 5-chloro-1,10-phenanthroline (Cl-phen), 4,4′-dichloro-2,2′-bipyridine (Cl 2 bpy), and 4,4′-bis(ethoxycarbonyl)-2,2′-bipyridine (EC-bpy). All of the compounds display solvatochromic absorption bands and solution luminescence, which are attributed to a common charge-transfer-to-diimine excited state. The excited-state energies can be tuned by approximately 1 eV through ligand variation. Solution lifetimes range from 1 ns to over 1000 ns and Φ em range from 6.4 × 10 -3 to less than 10 -5 in CH 2 Cl 2 . Based on these data, the nonradiative and radiative decay rate constants have been calculated. For the Pt(diimine)(tdt) series, the nonradiative decay rate constants increase exponentially with decreasing energy, in agreement with the Energy Gap Law, while those for the Pt(dbbpy)(dithiolate) complexes do not exhibit a similar correlation. Excited-state redox potentials have been estimated for all of the complexes from spectroscopic and electrochemical data. The ability to tune the driving force for bimolecular excited-state electron-transfer reactions has been demonstrated for eight of the complexes using reductive and oxidative quenching experiments.

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The synthesis, characterization, and photophysical properties of several Pt(II) complexes of quinoxaline-2,3dithiolate (qdt) and 6,7-dimethylquinoxaline-2,3-dithiolate (dmqdt) are described. Specifically, (TBA)2[Pt(qdt)2],where TBA = tetra-n-butylammonium, Pt(COD)(qdt), where COD = 1,5-cyclooctadiene, and Pt(phen)(qdt), where phen = 1,10-phenanthroline, and their dmqdt analogs have been prepared and examined with respect to their photophysical properties. Highly structured emission from Pt(COD)(qdt) in frozen glass solution at 77 K has been detected, having a major vibrational progression of 1370 cm-1 corresponding to a C=C stretching frequency of the quinoxalinedithiolate backbone. Solution luminescence from (TBA)2[Pt(qdt)2] and Pt(phen)(qdt) has been detected with quantum yields, <5em, of 10-5 and 10~3, respectively, although the latter is highly sensitive to solvent effects. The complex Pt(phen)(qdt) possesses a low-energy (Amax = 497 nm in CHCI3) absorption band assigned to a charge-transfer-to-diimine transition which exhibits a high degree of negative solvatochromism. Through both emission quantum yield and excited state lifetime measurements, the emissive excited state of Pt(phen)(qdt) is shown to undergo increasing degrees of nonradiative deactivation with increasing solvent polarity. Reductive quenching of the excited state of Pt(phen)(qdt) has been examined using the aromatic amines A,//-dimethyl aniline (DMA) and MMA'.iV'-tetramethylphenylenediamine (TMPD). From a Stem-Volmer analysis of the emission quenching data, quenching rate constants of 2.8 x 109 s_l (DMA) and 6.9 x 109 s_1 (TMPD) were calculated. Cyclic voltammetry was conducted on each of the complexes in order to probe further the nature of the HOMO and LUMO. From a simple thermochemical analysis, an excited state reduction potential of 1.14 V (vs NHE) has been estimated for Pt(phen)(qdt).

A series of mixed-ligand transition-metal diimine dithiolate complexes have been prepared, and their nonlinear optical properties have been investigated. Molecular hyperpolarizabilities have been obtained from electric field induced second harmonic generation experiments at 1.9 µm and range in magnitude from 0 to -39 × 10 -30 esu. Variation in molecular design of the complexes, through changes in the metal ion and diimine and dithiolate ligands, can be used to affect changes in the charge-transfer-to-diimine absorption band frequency and oscillator strength. Correlation between the optical charge-transfer transition and the nonlinear optical properties appears to agree with the two-state model.