Unsymmetric Ru(II) Complexes with N-Heterocyclic Carbene and/or Terpyridine Ligands: Synthesis, Characterization, Ground- and Excited-State Electronic Structures and Their Application for DSSC Sensitizers

Abstract

Three ruthenium(II) complexes with N-heterocyclic carbene (NHC) or NHC/2,2':6',2''-terpyridine (tpy) hybrid ligands, bis[2,6-bis(3-methylimidazol-3-ium-1-yl)pyridine-4-carboxylic acid]ruthenium(II) (BCN), [2,6-bis(3-methylimidazolium-1-yl)pyridine-4-carboxylic acid](2,2';6'2''-terpyridine)ruthenium(II) (TCN), and [2,6-bis(3-methylimidazol-3-ium-1-yl)pyridine](2,2';6'2''-terpyridine-4'-carboxylic acid)ruthenium(II) (CTN), have been synthesized and characterized by (1)H and (13)C NMR, high-resolution mass spectrometry, and elemental analysis. The molecular geometry of the TCN complex was determined by X-ray crystallography. Electronic absorption spectra of these complexes exhibit typical pi-pi* and metal-to-ligand charge transfer bands in the UV and visible regions, respectively. The lowest energy absorption maxima were 430, 448, and 463 nm with molar extinction coefficients of 28,100, 15,400, and 7400 M(-1)cm(-1) for BCN, TCN, and CTN, respectively. Voltammetric data suggest that energy levels of the highest occupied molecular orbitals (HOMOs) of the three complexes reside within a 10 meV window despite the varying degrees of electronic effect of the constituent ligands. The electronic structures of these complexes calculated via density functional theory (DFT) indicate that the three HOMOs and the three lowest unoccupied MOs (LUMOs) are metal and ligand centered in character, for the former and the latter, respectively. Time-dependent DFT (TD-DFT) calculation predicts that the lowest energy absorption bands of each complex are comprised of multiple one-electron excitations. TD-DFT calculation also suggests that the background of spectral red shift stems most likely from the stabilization of unoccupied MOs rather than the destabilization of occupied MOs. The overall efficiencies of the dye-sensitized solar cell systems of these complexes were found to be 0.48, 0.14, and 0.10% for BCN, TCN, and CTN, respectively, while that of a commercial bis(4,4'-dicarboxylato-2,2'-bipyridine)-bis(isothiocyanoto)ruthenium(II) (N719) system was 6.34%.

Tris(thiocyanate) Ruthenium(II) Sensitizers with Functionalized Dicarboxyterpyridine for Dye‐Sensitized Solar Cells

“…Synthetic route to the functionalized Ru II terpyridine sensitizers PRT-11-14; reagents and conditions: (i) Pd(PPh 3 ) 4 , K 2 CO 3 , THF, (ii) Bu n Li, SnBu n 3 Cl, À78 8C, (iii) PdCl 2 , PBu t 3 , CuI, CsF, DMF, 80 8C, (iv) RuCl 3 , ethanol, 90 8C, (v) complexes were then obtained from the reaction with RuCl 3 ·3H 2 O in ethanol, followed by treatment with tetrabutylammonium thiocyanate for the anion metathesis. [11] The crude ethoxycarbonyl ruthenium(II) products were then purified by flash chromatography on silica gel. Finally, ethoxycarbonyl groups were hydrolyzed in a mixture of acetone and a 1m solution of tetrabutylammonium hydroxide in methanol.…”

Ruthenium nitrosyl grafted carbon dots as a fluorescence-trackable nanoplatform for visible light-controlled nitric oxide release and targeted intracellular delivery

“…The compounds TPY COOH ((2,2′:6′,2″-terpyridine)-4′-carboxylic acid) and Ru(tpy COOH )Cl 3 were prepared according to the literature [28,29]. CDs were obtained according to previous reports [30,31].…”

Terpyridine and Quaterpyridine Complexes as Sensitizers for Photovoltaic Applications

“…C^N^C’ ligands have been tested by Park et al [142] in a series of bis-tridentate ruthenium complexes, exploiting N-heterocyclic carbenes such as 2,6-bis-(3-methylimidazolium-1-yl)pyridine ( 43a-c , Figure 33). …”

“…ORTEP drawing of complex 43b [142] (Reprinted with permission from Park, H.-J. ; Kim, K. H.; Choi, S. Y.; Kim, H.-M.; Lee, W. I.; Kang, Y. K.; Chung, Y. K. Unsymmetric Ru(II) Complexes with N-Heterocyclic Carbene and/or Terpyridine Ligands: Synthesis, Characterization, Ground- and Excited-State Electronic Structures and Their Application for DSSC Sensitizers.…”