Sexithiophenes mediated by MM quadruple bonds: MM = Mo2, MoW, and W2

The reactions between MM(TiPB)(4), where TiPB = 2,4,6-triisopropylbenzoate and MM = MoW and W(2), and the (2,2':5',2''-terthiophene)-5-carboxylic acid, TThH (2 equiv) leads to the formation of new compounds trans-MM(TiPB)(2)(TTh)(2), II and III, respectively, as well as to the previously reported compound I, when MM = Mo(2). The compounds have been characterized by elemental analysis, (1)H NMR spectroscopy, electronic absorption, and emission spectroscopies together with cyclic voltammetry and differential pulse voltammetry. Calculations on the model compounds I', II', and III', where formate ligands substitute for TiPB, have been carried out employing density functional theory (DFT) and time-dependent DFT. These complexes display intense (1)MLCT absorptions (MMdelta to thienyl carboxylate) and have oxidations and reductions that are metal (MMdelta) and thienyl ligand based, respectively. All compounds show emission in the near-IR region. At low temperature the NIR emission from I and II shows clear evidence of vibronic features due to upsilon(MM) approximately 350-390 cm(-1), and all compounds show evidence of a vibronic feature due to upsilon(CO(2)) approximately 1200 cm(-1). Transient absorption spectroscopy reveals relatively short-lived S(1) states, tau approximately 10 ps, and longer lived T(1) states: tau approximately 72 micros for I, approximately 160 ns for II, and approximately 90 ns for III. The chemistry described here reveals the remarkable influence of MMdelta to TTh pi electronic coupling on the optoelectronic properties of the thienyl chains.