MM quadruple bonds supported by cyanoacrylate ligands. Extending photon harvesting into the near infrared and studies of the MLCT states

Abstract

The compounds trans-M 2 (T i PB) 2 (L) 2 and trans-M 2 (T i PB) 2 (L 0 ) 2 have been prepared from the reactions between M 2 (T i PB) 4 (T i PB ¼ 2,4,6-triisopropylbenzoate, M ¼ Mo or W) and LH or L 0 H ($2 equiv.), respectively, whereThese cyanoacrylate ligands promote intense M 2 d to L or L 0 p*-transitions that span the range 550-1100 nm. The two molybdenum complexes have been characterized by single crystal X-ray studies that reveal the extensive L-M 2 -L or L 0 -M 2 -L 0 M 2 d-ligand p-conjugation. The new compounds have been characterized by electronic structure calculations employing density functional theory (DFT) and time-dependent-DFT, cyclic voltammetry, electronic absorption and steady state emission spectroscopy and femtosecond (fs) and nanosecond (ns) time resolved transient absorption (TA) and fs time-resolved infrared spectroscopy (TRIR). The latter allows the determination of the S 1 states as 1 MLCT that are delocalized over both L and L 0 . For molybdenum the T 1 states are 3 MoModd* whereas for tungsten they are 3 MLCT.

Molybdenum–molybdenum quadruple bonds supported by 9,10-anthraquinone carboxylate ligands. Molecular, electronic, ground state and unusual photoexcited state properties

“…compounds, where R is a p-acceptor such as thienyl, 19 p-C 6 H 4 CN 10 or cyanoacrylate, 6 the energy splitting of the LUMO and LUMO + 1, the in and out-of-phase p* combinations, is very small which indicates little involvement with the M 2 d orbital.…”

“…This does not preclude emission from the 1 MLCT state, but at 77 K uorescence is expected to be less intense than phosphorescence. 6 A plot showcasing the similarities in the emission spectra of 4. Depending upon the magnitude of ligand-Mo 2 d-ligand coupling this electronic excitation might be expected to have a signicant dipole moment change.…”

“…By using suitable pconjugated organic groups, R, and by the selection of the metal these intense electronic transitions can be tuned to span the visible region of the absorption spectrum and enter well into the near-IR, 400-1100 nm. 6,7 These 1 MLCT states have relatively long lifetimes, typically, 1-20 ps, that convert to even longerlived triplet T 1 states. We are evaluating the potential of these dimetal carboxylates for photon-harvesting applications and for studies of charge distribution in S 1 and T 1 states.…”

Modulating the M2δ-to-ligand charge transfer transition by the use of diarylboron substituents

“…The solvent of crystallization, THF, is coordinated axially along the Mo 2 bond, and the remainder of the structure is similar to M 2 tetracarboxylates previously reported. [4][5][6][7] The structure was, however, significantly disordered and was modeled accordingly. Further refinement details can be found in the ESI † and in the Crystallographic Information File (CIF).…”

“…Work in this lab has recently focused on the photophysical properties of carboxylate ligands attached to MM quadruply bonded centers and in particular to the metal-to-ligand charge transfer states of compounds of the form trans-M 2 (T i PB) 2 L 2 where L = a π-acceptor ligand such as cyanobenzoate, 4 cyanoacrylate, 5 α,α′-thienylcarboxylates 6 or a 2,6-azulenecarboxylate ester. 7 In these compounds the trans-L-M 2 -L geometry as seen in Fig.…”