Synthesis and photophysical characterization of a titanium(IV) phthalocyanine–C 60 supramolecular dyad Beatriz Ballesteros, a Gema de la Torre, a Toma ´s Torres, a, * Gordon L. Hug, b G. M. Aminur Rahman c and Dirk M. Guldi c, * a Universidad Auto ´noma de Madrid, Departamento de Quı ´mica Orga ´nica, Campus de Cantoblanco, 28049 Madrid, Spain b University of Notre Dame, Radiation Laboratory, Notre Dame, IN 46566, USA c Universita ¨t Erlangen, Institute for Physical and Theoretical Chemistry, Egerlandstr. 3, 91058 Erlangen, Germany Received 2 July 2005; revised 4 August 2005; accepted 8 August 2005 Available online 28 November 2005 Abstract—An axially substituted titanium(IV) phthalocyanine–fullerene donor–acceptor supramolecular dyad has been prepared by two different approaches, one of them representing a convenient convergent strategy. The dyad system exhibits photoinduced electron transfer upon irradiation with visible light to produce a microsecond lived charge separated state. q 2005 Elsevier Ltd. All rights reserved. 1. Introduction The unique electronic features of phthalocyanines (Pcs) 1 together with their unique stability and broad versatility has elicited a lot of interest in several fields of materials science, for example, as nonlinear optical media. 2 On the other hand, the combination of the light-harvesting and electron donor (or acceptor) characteristics of phthalocyanines 3 together with the electron accepting properties of fullerenes 4,5,6 is expected to give rise—ultimately—to efficient solar energy conversion. 7 Metal-directed self-assembly has recently become a major tool by which coordination chemists can prepare large and elaborate complexes from relatively simple components, as it provides the opportunity to control the properties of a material at the molecular level. In these cases the resulting metallo-supramolecular species are characterized by the large energies associated with metal–ligand bond formation. 8 Among the different metals that are coordinated by the centre of the Pc macrocycle, some of them, like titanium, bear axial ligands. The ability of axial coordination has been exploited by us to introduce an element of asymmetry to the Pc-molecule, thus preparing compounds with second order nonlinear optical (NLO) 9 and photoinduced electron transfer properties. 5b Catechol ligands are known building-blocks for metallo- supramolecular chemistry using Ti(IV). 8m,n Particularly, in the field of second harmonic generation, 2 we have recently studied a series of axially substituted titanium(IV) tetra-tert- butylphthalocyanines. 9 The introduction of a substituent in the axial position does affect dramatically the NLO response of phthalocyanines, since it breaks the centrosymmetry of the macrocycle, with the concomitant appearance of a dipole moment, and adds to the molecule a non-negligible octupolar character. Combination of dipole and octupolar features 10 within the same molecule has already yielded some other fairly interesting nonlinear optical properties in, for example, the field of axially-substituted subphthalo- cyanines. 11 In addition, axial substitution with bulky groups such as substituted catecholates helps to prevent aggre- gation of macrocycles. 12 In fact, phthalocyanines emerged as promising sensitiser materials for dye sensitised solar cells (DSSC) 13 as well as other photovoltaic systems, 7 but their applications in this field have been limited, in large, by problems associated with aggregation of the dye on the metal oxide surface. In this context, we have recently shown that anchoring a novel titanium phthalocyanine to nanocrytalline TiO 2 films occurs with inappreciable aggregation. 12 The observation of state selective electron injection from the titanium phthalo- cyanine to the TiO 2 with efficient charge separation prompted us to prepare titanium phthalocyanine-based 0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.tet.2005.08.126 Tetrahedron 62 (2006) 2097–2101 Keywords: Phthalocyanine; Fullerene; Titanium(IV); Electron transfer. * Corresponding authors. Tel.: C34 91 397 5097; fax: C34 91 397 3966 (T.T.); tel: C49 9131 8527340; fax: C49 9131 8528307 (D.M.G.); e-mail addresses: tomas.torres@uam.es; dirk.guldi@chemie.uni-erlangen.de