Page - 32 - in Photovoltaic Materials and Electronic Devices

Materials 2016, 9, 137 15 of 37 Figure 19. Tpy extended with substituted stiryl moieties by Giribabu [102]. 3.2.2. Bis-Terpyridine Stergiopoulos et al., in 2005 [106], replaced all the thiocyanates with another terpyridine. In the resulting heteroleptic complex, one tpy was substituted in 4’- with a p-iodophenyl moiety and the other one with a p-phenylphosphonic acid, in order to allow the grafting to TiO2 semiconductor in a solid state device (26, Figure 20). Figure 20. Bis-tpy complex proposed by Stergiopoulos et al. [106]. In the same year Houarner et al. [107] proposed another bis-tpy complex with a phosphonic acid as the anchoring group on one terpyridine and oligothiophene moieties on the other one, in order to increase the interaction between dye and hole transporting material (27, Figure 21). Low performances of this class were attributed to an undesired localisation of the LUMO orbital on thiophenes and, as a consequence, to a difficult charge injection into the TiO2. In order to improve the performances, the same group in 2007 introduced an unconjugated bridge between the tpy and the polythiophene moiety [108]. Figure 21. A first series of bis-tpy complexes proposed by Houarner et al. [107]. Further improvements to the Houarner series were reported in 2007 [109] by introducing a thiophene π-conjugated bridge between the terpyridine and the phosphonate anchoring group, Figure19. TpyextendedwithsubstitutedstirylmoietiesbyGiribabu[102]. 3.2.2. Bis-Terpyridine Stergio oulos et al. i 2005 [106], replaced all the thiocyanates with another terpyridine. Intheresultingheterolepticcomplex,onetpywassubstitutedin4’-with ap-iodophenylmoietyandtheotheronewithap-phenylphosphonicacid, inorder toallowthegrafting toTiO2 semiconductor inasolidstatedevice (26, Figure20). Materials 2016, 9, 137 15 of 37 Figure 19. Tpy extended with substituted stiryl moieties by Giribabu [102]. 3.2.2. Bis-Terpyridine S ergi poulos et al., i 2005 [106], replaced all the thiocyanates with anoth r terpyridine. In the resulting heteroleptic co plex, one tpy was substituted in 4’- with a p-iodophenyl moiety and the other one with a p-phenylphosphonic acid, in order to allow the grafting to TiO2 semiconductor in a solid state device (26, Figure 20). Figure 20. Bis-tpy complex proposed by Stergiopoulos et al. [106]. In the same year Houarner et al. [107] proposed another bis-tpy complex with a phosphonic acid as the anchoring group on one terpyridine and oligothiophene moieties on the other one, in order to increase the interaction between dye and hole transporting material (27, Figure 21). Low performances of this class were attributed to an undesired localisation of the LUMO orbital on thiophenes and, as a consequence, to a difficult charge injection into the TiO2. In order to improve the performances, the same group in 2007 introduced an unconjugated bridge between the tpy and the polythiophene moiety [108]. Figure20. Bis-tpycomplexproposedbySte giopoulos et al. [106]. In thesameyearHouarner et al. [107]proposedanotherbis-tpycomplexwith a phosphonic acid as the anchoring group on one terpyridine and oligothiophene moieties on the other one, in order to increase the interaction between dye and hole transporting material (27, Figure 21). Low performances of this class were attributedtoanundesired localisationof theLUMOorbitalonthiophenesand,as aconsequence, toadifficult charge injection into theTiO2. Inorder to improvethe performances, thesamegroupin2007 introducedanunconjugatedbridgebetween the tpyandthepolythiophenemoiety [108]. 32