A series of alkyl-substituted and unsubstituted poly(3,4-alkylenedioxythiophene)s were synthesized electrochemically using 3,4-alkylenedioxythiophene derivative monomers where either the size of the alkylenedioxy ring or the nature of the pendent group was varied. The specific systems studied include 3,4-ethylenedioxythiophene (EDOT), 2-methyl-2,3dihydrothieno [3,4-b][1,4] (BuDOT-Xyl). Optoelectrochemical experiments revealed that the nature of the substitution on the polymers had little effect on the extent of conjugation of the backbone as evidenced by electronic band gaps for all polymers of approximately 1.7 eV (730 nm). These electrochromic polymers switch from a relatively transmissive light green in the oxidized form to an opaque dark blue in the reduced form, with the highest electrochromic contrast ratios accessible for PBuDOT and PEDOT-C 14 H 29 . Multiple switching studies monitoring the electrochromic contrast showed that ca. 300 nm thick polymer films could be fully switched between their reduced and oxidized forms in 0.8-2.2 s with ∆%T of 44-63%. In situ conductivity studies carried out on relatively thick polymer films (2.7-9.5 µm) deposited between large gap (200 µm) lateral growth electrodes demonstrated the lowpotential turn-on for these materials, and maximum conductivities of 0.2-12.1 S/cm were attained.

A series of four platinum acetylide complexes that contain 4-ethynylstilbene (4-ES) ligands have been subjected to a detailed photochemical and photophysical investigation. The objective of the work is to understand the structure and reactivity of the lowest excited states in π-conjugated Pt-acetylides. The 4-ES ligand was chosen for this work because the excited-state properties of the stilbene chromophore are well understood. In particular, stilbene features fluorescence and phosphorescence, and also undergoes trans-cis photoisomerization from the triplet excited state. Two of the complexes investigated contain phosphine ligands and have the structures trans-Pt(PBu 3 ) 2 (4-ES) 2 and cis-Pt(dppe)(4-ES) 2 (2 and 3, respectively, where PBu 3 ) tributylphosphine and dppe ) bis-1,2-diphosphinoethane). The other two complexes contain substituted 2,2′-bipyridine ligands and have the structures Pt(t-Bu-bpy)(4-ES) 2 and Pt(4,4′-CO 2 Et-bpy)(4-ES) 2 (3 and 4, respectively, where t-Bubpy ) 4,4′-di-tert-butyl-2,2′-bipyridine and 4,4′-CO 2 Et-bpy ) 4,4′-bis(carboethoxy)-2,2′-bipyridine). The crystal structure of 2 is reported. The complex features a square planar PtP 2 C 2 geometry and the planes of the phenyl groups in the 4-ES ligands are twisted approximately 60°relative to the plane defined by the PtP 2 C 2 core. The series of complexes was examined by using absorption, variable-temperature photoluminescence, and transient absorption spectroscopy. In addition, the photochemical reactivity of the complexes was explored by UV-visible absorption and NMR spectroscopy. The available experimental data indicate that in all of the complexes excitation leads to high-yield production of a 3 π,π* excited state that is localized on one of the 4-ES ligands. At low temperatures, the 3 π,π* state exhibits strong phosphorescence that is very similar to the phosphorescence of trans-stilbene. At temperatures above the glass-to-fluid temperature of the solvent medium, the 3 π,π* state decays rapidly (τ ≈ 40 ns). The decay pathway is believed to involve rotation around the CdC bond of one of the 4-ES moieties. This model is supported by the photochemical results, which show that steady-state photolysis leads to trans-cis isomerization of one of the 4-ES ligands with a quantum efficiency of 0.4.

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The synthesis, isolation, and metalation of the trianionic PrNCNLi 3 ] 2 (2) is described. The terdentate coordination ability of 2 is demonstrated in the synthesis of the hafnium dichloride anion [2,6-i PrNCNHfCl 2 ]-[Li(DME) 3 ] (3-DME). Complex 3-DME is distorted square pyramidal in the solid state, but NMR eVidence indicates the complex is fluxional and trigonal bypyramidal in solution. Straightforward ligand modification proVides the additional trianionic pincer ligand [3,5-MeNCNLi 2 ] 2 [Li 2 (DME) 6 ] ( 5). This sterically smaller ligand leads to the hafnium pincerate dianion complex [(3, 2 Hf][Li 2 (DME) 2 ] ( 6), which contains two trianionic pincer ligands. The new compounds are characterized by elemental analysis, multinuclear NMR, and X-ray diffraction crystallography.