Photoredox vs. energy transfer in a Ru(ii)–Fe(ii) supramolecular complex built with an heteroditopic bipyridine-terpyridine ligand

Abstract

A trinuclear [[Ru(II)(bpy)(2)(bpy-terpy)](2)Fe(II)](6+) complex (I) in which a Fe(II)-bis-terpyridine-like centre is covalently linked to two Ru(II)-tris-bipyridine-like moieties by a bridging bipyridine-terpyridine ligand has been synthesised and characterised. Its electrochemical, photophysical and photochemical properties have been investigated in CH(3)CN and compared with those of mononuclear model complexes. The cyclic voltammetry of (I) exhibits, in the positive region, two successive reversible oxidation processes, corresponding to the Fe(III)/Fe(II) and Ru(III)/Ru(II) redox couples. These systems are clearly separated (DeltaE(1/2) = 160 mV), demonstrating the lack of an electronic connection between the two subunits. The two oxidized forms of the complex, [[Ru(II)(bpy)(2)(bpy-terpy)](2)Fe(III)](7+) and [[Ru(III)(bpy)(2)(terpy-bpy)](2)Fe(III)](9+), obtained after two successive exhaustive electrolyses, are stable. (I) is poorly luminescent, indicating that the covalent linkage of the Ru(II)-tris-bipyridine to the Fe(II)-bis-terpyridine subunit leads to a strong quenching of the Ru(II)* excited state by energy transfer to the Fe(II) centre. Luminescence lifetime experiments show that the process occurs within 6 ns. The nature of the energy transfer process is discussed and an intramolecular energy exchange is proposed as a preferable deactivation pathway. Nevertheless this energy transfer can be efficiently quenched by an electron transfer process in the presence of a large excess of the 4-bromophenyl diazonium cation, playing the role of a sacrificial oxidant. Finally complete photoinduced oxidation of (I) has been performed by continuous photolysis experiments in the presence of a large excess of this sacrificial oxidant. The comparison with a mixture of the corresponding mononuclear model complexes has been made.

Alternated bimetallic [Ru–M] (M = Fe2+, Zn2+) coordination polymers based on [Ru(bpy)3]2+ units connected to bis-terpyridine ligands: synthesis, electrochemistry and photophysics in solution or in thin film on electrodes

“…1 and SI4 †). 27 The rst one, located at E 1/2 ¼ À1.52 V, corresponds to the reduction of one terpyridine ligand of the Fe(II) unit (eqn (3)). 1C).…”

“…6 30 The bi-exponential decay of [{Ru II -Zn II } n ] 4n+ can thus be the result of the polymer structure and may be due to some self quenching process between the excited state of the Ru(II) centers located in a close environment as a consequence of the folding of the polymer chain. The quenching rate constant (k q ) occurring in [{Ru II -M II } n ] 4n+ can be calculated according to eqn (8): 27 [{Ru II -M II } n ] 4n+ has been electrodeposited on the ITO electrode following the procedure described in the previous section. Such decay has been also observed when coordination complexes are part of the polymer backbone as with the [Re(CO) 2 (bpy)PP] n polymer where PP is a bidentate phosphorus ligand.…”

Catalytic Light‐Triggered Reduction Promoted by a Dithienylethene Derivative

“…In order to illustrate this phenomenon, the light-triggered reduction of iron(III) bisterpyridine( [Fe(tpy) 2 ] 3 + )i nt he presence of the photochromic core 1 2 + + is followed using absorption spectroscopy.I ndeed, [Fe(tpy) 2 ] 2 + has interesting optical and electrochemical properties: [31] a) av ery intense MLCT band (extinction coefficient % 12000 Lmol À1 cm À1 )l ocated at 550 nm ( Figure S1 b), b) the Fe III /Fe II redox potential is located at + 0.75 Vv s. Ag/Ag + ( Figure S4), well in the range for testing the photoreducing character of the considered DTE derivative.…”

A new polymorph of 4′-tolyl-2,2′:6′,2′′-terpyridine (ttpy) and the single crystal structures of [Fe(ttpy)2][PF6]2 and [Ru(ttpy)2][PF6]2

“…The complex [Fe(ttpy) 2 ][PF 6 ] 2 has previously been prepared in 42% yield from FeSO 4 Á 7H 2 O and ttpy in EtOHÀH 2 O with a 2 h period of reflux [18]. The complex can also be conveniently prepared in over 80% yield from FeCl 2 Á 4H 2 O and ttpy in ethanol at room temperature [34].…”

“…The facile bromination of ttpy to give 4 0 -(4-bromomethylphenyl)-2,2 0 :6 0 ,2 00 -terpyridine, (Brttpy), provides a starting point for the synthesis of functionalized tpy ligands [see, for example, [4][5][6][7][8][9][10][11][12] and dendrimers [13]. Many of the metal complexes developed through the use of the ligands ttpy and Brttpy are of importance because of their redox or photophysical properties [4,5,7,9,[14][15][16][17][18]. Despite the interest in the ttpy ligand, its solidstate structure was only reported in 2007 [19], and structural details of homoleptic [M(ttpy) 2 [21], and a report of [Cu 6 (CN) 8 Á Fe(ttpy) 2 ] n in which the [Fe(ttpy) 2 ] 2+ ions are encapsulated within a 3-dimensional anionic network [22].…”