Covalent and Noncovalent Phthalocyanine-Carbon Nanostructure Systems: Synthesis, Photoinduced Electron Transfer, and Application to Molecular Photovoltaics Giovanni Bottari, † Gema de la Torre, † Dirk M. Guldi,* ,‡ and Toma ´s Torres* ,†,§ Departamento de Quı ´mica Orga ´nica, Universidad Auto ´noma de Madrid, 28049 Madrid, Spain, IMDEA-Nanociencia, Facultad de Ciencias, Ciudad Universitaria de Cantoblanco, 28049 Madrid, Spain, and Department of Chemistry and Pharmacy and Interdisciplinary Center for Molecular Materials (ICMM), Friedrich-Alexander-Universita ¨t Erlangen-Nu ¨rnberg, Egerlandstrasse 3, 91058 Erlangen, Germany Received July 17, 2009 Contents 1. Introduction 6768 2. Phthalocyanine-Fullerene Donor-Acceptor Systems 6771 2.1. Covalently Linked Phthalocyanine-Fullerene Systems 6771 2.2. Phthalocyanine-Fullerene Supramolecular Systems 6783 3. Subphthalocyanine-Fullerene Donor-Acceptor Systems 6786 3.1. Covalently-Linked Subphthalocyanine-Fullerene Systems 6786 3.2. Subphthalocyanine-Fullerene Supramolecular Systems 6788 4. Phthalocyanines and Subphthalocyanines Connected to Related Acceptor Systems 6788 5. Decoration of Carbon Nanotubes with Phthalocyanines 6791 5.1. Covalent Attachment of Phthalocyanines to Carbon Nanotubes 6792 5.2. Noncovalent Interactions between Phthalocyanines and Carbon Nanotubes 6794 6. Photophysics of Phthalocyanine- and Subphthalocyanine-Carbon Nanostructure Systems 6797 6.1. Nonspecific, Intermolecular Interactions between Phthalocyanines and Fullerenes in Solution 6797 6.2. Photophysics of Phthalocyanine-Fullerene Systems 6797 6.3. Photophysics of Subphthalocyanine-Fullerene Systems 6802 6.4. Photophysics of Phthalocyanine-Carbon Nanotube Assemblies 6803 7. Phthalocyanines and Fullerene as Active Components in Organic Solar Cells 6804 7.1. Phthalocyanine/Fullerene Blends as Active Layers 6804 7.2. Two-Layer Phthalocyanine/Fullerene Heterojunction Devices 6808 7.3. Covalent Phthalocyanine-Fullerene Systems as Components of Photoactive Layers 6810 8. Conclusions and Outlook 6811 9. Abbreviations 6811 10. Acknowledgments 6812 11. Note Added after ASAP Publication 6812 12. References 6812 1. Introduction Photosynthesis is used by nature to convert light energy into chemical energy in some living systems. In such a process, a cascade of very efficient, short-range energy and electron transfer events between well-arranged, light-harvest- ing organic donor and acceptor pigments takes place within the photosynthetic reaction center, leading to the overall generation of chemical energy from sunlight with near quantum efficiency. 1-8 During the past decade, a significant effort has been made by the scientific community toward the preparation of synthetic model compounds of natural photosynthetic sys- tems able to convert light into other energy sources, 9 probably fostered by the increasing concerns related to the utilization of fossils fuels for the production of electricity in terms of both availability and environmental issues. However, considering the structural complexity presented by the natural photosynthetic systems, much of the scientific effort has been devoted toward the preparation and study of structurally simpler systems, with the aim of reproducing some of the fundamental steps occurring in natural photo- synthesis, one of the most important being the photoinduced charge separation (CS). 10-12 Among the chromophores that have been used as molec- ular components in artificial photosynthetic systems, por- phyrinoids, the ubiquitous molecular building blocks em- ployed by nature in natural photosynthesis, have been the preferred and obvious choice, due to their intense optical absorption and rich redox chemistry. 13-20 Within the large family of porphyrinoid systems, phtha- locyanines (Pcs) enjoy a privileged position (Figure 1a). These chromophores, which have a two-dimensional 18-π- electron aromatic system isoelectronic with that of porphyrins (Pors), possess in fact unique physicochemical properties which render these macrocycles valuable building blocks in materials science. 21-32 Pcs are thermally and chemically stable compounds which present an intense absorption in the red/near-infrared (IR) region of the solar spectrum with extinction coefficients (as high as 200 000 M -1 cm -1 ) and fluorescence quantum yields * To whom correspondence should be addressed. E-mail: tomas.torres@uam.es (T.T.); dirk.guldi@chemie.uni-erlangen.de (D.M.G.). † Universidad Auto ´noma de Madrid. ‡ Friedrich-Alexander-Universita ¨t Erlangen-Nu ¨rnberg. § IMDEA-Nanociencia. Chem. Rev. 2010, 110, 6768–6816 6768 10.1021/cr900254z  2010 American Chemical Society Published on Web 04/05/2010