Linear Multinuclear Ru^II Photosensitizers

Abstract

Keywords: Ruthenium / Tridentate ligands / Bridging ligands / Electron transfer / PhotochemistryFour ditopic bridging ligands, containing 2,2Ј:6Ј,2ЈЈ-terpyridine and 2,6-dipyrazinylpyridine (dpp) metal-binding units attached through p-or m-phenylene linkages, have been incorporated into eight mono-, di-and trinuclear linear Ru II complexes. These were characterized by UV/Vis spectroscopy and cyclic voltammetry, and by their ability to undergo light-induced electron transfers to methylviologen. The dpp-

(Polypyridyl)ruthenium(II) Complexes Based on a Back‐to‐Back Bis(pyrazolylpyridine) Bridging Ligand

“…This electronic situation strongly reminds of the complex [(ttpy)-Ru(tpy-ph-tpy)Ru(ttpy)][PF 6 ] 4 [where ttpy is 4Ј-p-tolyl-2,2Ј:6,2ЈЈ-terpyridine and tpy-ph-tpy is 1,4-bis(2,2Ј:6,2ЈЈ-terpyridin-4Ј-yl)benzene] involving the analogous tpy bridging ligand. [19,24] The reduction of complex 1 reveals four well-separated and equally intense waves, which are fully reversible up to the second reduction. After the third reduction, the electrochemical reversibility is partially lost.…”

Ruthenium(II) Complexes of Carboxylated Terpyridines and Dipyrazinylpyridines

“…[2,14] In this work, we used a one-pot synthesis of H1 at room temperature from 2-acetylpyridine and 4-carboxybenzaldehyde (the ethyl ester of which can be used just as well) in the presence of KOH and NH 4 OH in aqueous MeOH (Scheme 1), a process that we have previously used to prepare several 4Ј-substituted terpyridines and dipyrazinylpyri-dines. [9,10,16,17] This precipitates a salt form which, after redissolving, was acidified to precipitate analytically pure H1 in 80 % yield. The free ligand lacking the spacer, terpyridine-4Ј-carboxylic acid H2, was first isolated as an unintended byproduct of a convergent preparation of its ethyl ester by Stille coupling, in 4 steps and 28 % overall yield from commercial citrazinic acid.…”

Catechol‐Bearing Dipyrazinylpyridine Complexes of Ruthenium(II)

“…This enabled the operation of an electrostatically advantaged reductive quenching mechanism in photosensitization experiments using other dpp complexes. [9] Scheme 1.…”

“…The first member of the dipyrazinylpyridine (dpp) family of ligands, the 4-p-tolyl derivative 1 (Scheme 1), was prepared in a remarkable onestep reaction of commercial materials, in excellent yield and without purification. [6] We have since used this procedure to prepare other dpp examples, [7][8][9] and extended it to terpyridine synthesis, although those reactions were slower. [9,10] Besides their easier syntheses, the homoleptic Ru II complex [Ru (1) 2 ] 2+ revealed an additional advantage of dpp ligands over other tridentates: a longer excited-state lifetime, τ (18 ns at room temperature), [6] compared to that of the analogous terpyridine complex [Ru(ttpy) 2 ] 2+ [0.95 ns, [11] ttpy is 4Ј-(4-tolyl)-2,2Ј:6Ј,2ЈЈ-terpyridine], a result which can be attributed to the electron-withdrawing effect of the additional nitrogen atoms in stabilizing the ligand π* orbital relative to metal-centred orbitals.…”

“…Samples of all four new complexes were submitted to the assessment protocol [23] that we have used several times to gauge photosensitizer ability [9,12,14,24,25] 2+ and TEOA, were all required to produce the precipitation. We also found that no precipitation occurred in the dark; light -even sunlight through a window -was required.…”