Heterobimetallic complexes of transition metals and rare earths as promising candidates in dye sensitized solar cells and OLEDs

The intrinsic characteristics of good fluorophore to develop new materials to be used as Dye-Sensitized Solar Cells (DSSC) and Organic Light Emitting Diodes (OLED) are the photophysical and photoelectronic properties related to the optical and/or electric excitation. This work presents the investigation of the complexation reaction of nine nitrogen-chelating ligands (2,2'-bipyridine and the corresponding dimethyl-, dicarboxy-, dicarbethoxy- and diaminonaphtyl- 4,4´-functionalized derivatives, 1,10-phenanthroline and the analogous 5,6-dione, 2,3,7,8-tetra-aminodibenzo[1,4]dioxin and its 4,5,9,12,21,24-hexaaza-10,23-dioxabenzo-heptacene derivative with extended π system) with transition metals such as Ru(II) and Ir(III). In total, thirty-six metallic complexes were synthesized and characterized: 31 monometallic, 3 homobimetallic (1 Ir-Ir and 2 Ru-Ru) and 2 heterobimetallic. Additionally, one monometallic complex with Eu and another one with La were prepared, as well two heterobimetallic complexes between Ru-La and Ru-Eu. Promising results were obtained, such as solubility in several solvents, which facilitates the process of deposition or formation of fluorophore film in the construction of DSSC and OLED devices. Besides, the intensification of photophysical properties was also observed, due to the structural modification of the ligands, through the alternation between donor groups and acceptors of electronic density, -NH₂, -CO₂H and -CO₂R (R= CH₂CH₃, CH₂CH₂OH). There was an increase in the quantum fluorescence yield (ϕ) when comparing the Ru carboxylic complex [Ru(dcbpy)2(fend)](PF₆)₂ 15 (𝝓 = 0.19) (4,4'-dicarboxi-2,2'-bipyridine and fend = 1,10- phenanthroline-5,6-dione) with the carbethoxylic analogue [Ru(deeb)₂(fend)](PF₆)₂, 16 (ϕ = 0.02) (deeb = 4,4'-dietoxicarbonyl-2,2'-bipyridine). An increase in the molar absorptivity coefficient (ε, 104 Lmol^-1 cm^-1 ) was obtained comparing the carboxylic complexes 15 (ε = 1.80) and complex [Ru(dcbpy)2(fenox)](PF₆)₂, 18 (ε = 3.84) (fenox = benzo[5,6][1,4]dioxino[2,3-i]dipyrido[3,2-a:2',3'-c]phenazine-13,14-diamine), due to the increase in the extended π system in the latter. Furthermore, an increase in the value of the same parameters, ϕ and ε, was also observed when comparing monometallic Ru complex 16 (ε = 1.80 and ϕ = 0.02) with [Ru(deeb)2(µ-fenazin)(deeb)2Ru](PF₆)₄, 33 (ε = 4.91 and ϕ = 0.08) (fenazin = 4,5,9,12,21,24-Hexaaza-10,23-dioxabenzo[a,c,p,r] heptacene), The increase in ϕ value was also noticed when the obtained photochemical results from the bis-naphtylamide complex [Ru(dcbpy)2(CONH-2-Nft)](PF6)2 8 (ϕ = 0.05) (CONH-2-Nft = N4,N4'-di(naphthalene-2-yl)-4,4'-dicarboxamide-2,2'-bipyridine were compared to those obtained from [Ru(CONH-2-Nft)₃](PF₆)₂, 14 (ϕ = 0.16). It is important to mention that the molecular structure of 8 was determined by X-ray crystallography. Finally, the obtained results showed that these complexes may be promising fluorophores on photoelectronic devices, such as DSSC and OLED. (author)