Journal of Photochemistry and Photobiology A: Chemistry 150 (2002) 167–175 Syntheses of mixed ligands complexes of Ru(II) with 4,4 ′ -dicarboxy-2,2 ′ -bipyridine and substituted pteridinedione and the use of these complexes in electrochemical photovoltaic cells S. Anandan, S. Latha, P. Maruthamuthu ∗ Department of Energy (Chemistry-Interdisciplinary), University of Madras, Guindy Campus, Chennai 600 025, Tamil Nadu, India Received 6 November 2001; received in revised form 17 January 2002; accepted 6 February 2002 Abstract The synthesis, spectral and photoelectrochemical studies of mixed ligand complexes of [Ru(dcbpy) 2 (LL)]Cl 2 , where LL = 2,4-(1,3-N,N ′ - dimethyl)pteridinedione (DMP), 6,7-dimethyl-2,4-(1,3-N,N ′ -dimethyl)pteridinedione (MDMP), 6,7-diphenyl-2,4-(1,3-N,N ′ -dimethyl) pteridinedione (PhDMP), dibenzo[h,j]-(1,3-N,N ′ -dimethyl)isoalloxazine (BIAlo), 6,7-bis(pyrid-2-yl)-2,4-(1,3-N,N ′ -dimethyl) pteridine- dione (PyDMP) were carried out. These complexes were attached to sol–gel processed TiO 2 electrodes and the photocells fabricated were illuminated with polychromatic radiation in the presence of I 2 /I 3 - as redox electrolyte. The incident photon to current conversion efficiency determined was found to be ∼20–48%. © 2002 Elsevier Science B.V. All rights reserved. Keywords: TiO 2 ; Pterdinedione; Isoalloxazine; Dye sensitization; Solar cells 1. Introduction In recent years, considerable amount of research in the field of photochemistry has been directed towards photo- chemical and photoelectrochemical processes applicable to solar energy conversion processes [1–6]. It is well known that photoelectrochemical cells could be used for solar en- ergy conversion into electricity as well as for production of chemical fuels. The basic principles and mechanisms involved in such systems have been reviewed [7–10] elab- orately. At present, the most promising method for light to electrical conversion is via photosensitized TiO 2 nanocrys- talline electrode with Ruthenium(II) polypyridyl complexes [11–15]. For the past several years, polypyridyl ruthe- nium(II) complexes containing 4,4 ′ -dicarboxy-2,2 ′ -bipyri- dine as a photosensitizer attached to nanocrystalline TiO 2 have been widely studied in solar energy conversion pro- cesses [12,16–29]. For example, cis-bis(thiocyanato)bis(2, 2 ′ -bipyridyl-4,4 ′ -dicarboxylato) Ru(II) is found to be an outstanding solar light absorber and charge transfer sensi- ∗ Corresponding author. Fax: +91-44-2352-494. E-mail addresses: pmaruthu@satyam.net.in, pmaruthu@yahoo.com (P. Maruthamuthu). tizer [16,30–32] unmatched by any other dyestuff known so far. A good understanding of the charge transport in the nanostructured materials is of great importance for the de- velopment of an efficient solar cell. Different mechanisms for the charge transport have been discussed [33–38]. In nature, many biologically important compounds take part in electron transfer processes and act as one electron or two electron transfer agents. For instance, Flavin coen- zymes transfer electrons to and from heme and iron–sulfur and molybdenum centers in proteins. They also serve as a required electron pair splitting or joining interface be- tween metal one-electron donors or acceptors and organic two electron oxidants or reductants [39–41]. Pteridines are fused-ring nitrogen heterocyclic compounds that form the core structure of folates. They are found to function as cofactors for enzymes involved in hydroxylation [42] and methyl transfer [43,44]. They also act as redox mediator [45] and pigments for eyes and wings in certain insects [46] and in synthesis of anticancer drug [47,48]. The majority of the naturally occurring pteridine compounds have the 2-amino-4-oxo substitution pattern on the bicyclic core and have the trivial class name pterin. Fusion of a third benzene ring to a 2,4-dioxo-substituted pteridine group produces the core structure of the isoalloxazines, of which flavins are a subgroup. Certain enzymes for which pterins are cofactors, 1010-6030/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S1010-6030(02)00094-1