Synthesis and Characterization of Ruthenium(II) Molecular Assemblies for Photosensitization of Nanocrystalline TiO₂:  Utilization of Hydroxyl Grafting Mode

Abstract

New Ru polypyridine complexes [(bpy)2Ru(L)]2+, where bpy = 2,2'-bipyridine and L = dipyrido[3,2-a:2',3'-c]-phenazine-2-carboxylic acid (dppzc), dipyrido[3,2-f:2',3'-h]quinoxaline-2,3-dicarboxylic acid (dpq(COOH)2), 3-hydroxydipyrido[3,2-f:2',3'-h]quinoxaline-2-carboxylic acid (dpq(OHCOOH)), 2,3-dihydroxydipyrido[3,2-f:2',3'-h]quinoxaline (dpq(OH)2), and [(L')Ru(dppzc)2]2+, where L' = bpy and 1,10-phenanthroline (phen), have been synthesized, characterized, and anchored to nanocrystalline TiO2 electrodes for light to electrical energy conversion in regenerative photoelectrochemical cells with I-/I2 acetonitrile electrolyte. These sensitizers have intense metal-to-ligand charge-transfer (MLCT) bands centered at approximately 450 nm. The effect of pH on the absorption and emission spectra of these complexes consisting of protonatable ligands has been investigated in water by spectrophotometric titration. The excited-state pKa values are more basic than the ground-state ones, except the pKa2 and pKa2* in [(bpy)2Ru(dpq(OH)2)]2+, which are equal, suggesting the localization of the lowest-energy MLCT on heteroaromatic bridging ligands, dppzc and dpq. Incident photon-to-current conversion efficiency (IPCE) is sensitive to the structural changes that resulted from introducing different functional groups, used for grafting.

pH- and DNA-induced dual molecular light switches based on a novel ruthenium(II) complex

“…This family of complexes were thus termed as ''DNA molecular light switches'' [60]. Usually, the DNA light switching behaviors observed are due to the following three possibilities resulting from a noncovalent intercalative binding mode: (i) the protection of the intercalative moieties from interacting with water which was facilitated by formation of intermolecular hydrogen bonds, or excited protontransfer reaction [22,35]; (ii) more hydrophobic environment [61]; (iii) a higher rigidity of the local environments of the complexes, decreasing nonradiative vibrational modes of relaxation [62]; and (iv) binding of the complexes to DNA bases results in an increase in energy of the dark (nonluminescent) state, a MLCT transition from Ru(II) to the phenazine portion, that is diminishing the energy separation between the dark state and the bright (luminescent) state, a result of charge transfer from the metal center to the bpy portion, thus making the emissive state thermally accessible and turning on the emission [4,61,63]. As shown in Fig.…”

Template-directed formation of luminescent lanthanide complexes: Versatile tools for colorimetric identification of single nucleotide polymorphism

“…The NHS (N-hydroxysuccinimide) ester of iminodiacetic acid diethyl ester (1) [44], 5-carboxy-1,10-phenanthroline (3) [45], dipyrido[3,2-a:2 0 , 3 0 -c]phenazinecarboxylic acid (5) [46], and 2,2 0 :6 0 ,2 00 -terpyridine-4 0 -carbonitrile (7) [47] were prepared as previously reported.…”

Cyclometalated iridium(III) complex of 6‐hydroxydipyrido[3,2‐a:2′,3′‐c]phenazine: synthesis, and acid–base and avid DNA binding properties

“…The pK a2 is comparable with the pK a = 7.20-7.40 reported for [Ru(bpy) 2 (hdppz)] 2+ , [30] and more acidic than pK a = 8.6 reported for [Ru(bpy) 2 [51] mainly owing to the fact that hdppz is more conjugated than hpbpy. However, the pK a2 value of 6.96 is more basic than hydroxy-deprotonated pK a of 6.0 (the first hydroxy) for [Ru(bpy) 2 dpq(OH) 2 ] 2+ {dpq(OH) 2 = 2,3-dihydroxydipyrido[3,2-f :2 ,3 -h]quinoxaline}, and 6.4 for [Ru(bpy) 2 (dpqOHCOOH)] 2+ (dpqOHCOOH = 3-hydroxydipyrido[3,2-f :2 ,3 -h]quinoxaline-2-carboxylic acid), [52] owing to intra-molecular H-bonding effects.…”