Due to their photoproperties and easy chemical functionalisations, phthalocyanines are amongst the most promising advanced photosensitisers for photodynamic therapy of cancer.

Phthalocyanines and porphyrins are versatile functional pigments with a wide range of applications. These macrocyclic compounds contain four isoindole or pyrrole nitrogen atoms, which can complex with a range of metal ions. Large rare earth metal ions can bring together these tetrapyrrole derivatives to form sandwich-type double- and triple-decker complexes. Depending on the metal centers and the nature of the macrocyclic ligands, these compounds exhibit tunable spectroscopic, electronic, and redox properties, and different extents of intramolecular pi-pi interactions. Some of the properties of the sandwich-type complexes are unique and enable them to be used as advanced materials for various applications. Over the last two decades, a vast number of homoleptic and heteroleptic double- and triple-decker complexes have been synthesized. With improvements in synthetic procedures, researchers have prepared novel sandwich complexes that could not have been prepared by traditional methods. This Account highlights our work over the last decade on this important class of compounds. We have focused both on the development of facile and efficient synthetic methodology and on the various properties and potential applications of these complexes. For both the double- and triple-decker series, we have performed systematic investigations on several series of closely related analogues to reveal the correlations among the structures, electronic properties, spectroscopic characteristics, electrochemistry, and degree of pi-pi interactions. We have also performed detailed studies of the self-assembly of amphiphilic analogues in Langmuir-Blodgett films, metal-induced assembly of crown ether containing sandwich compounds, and the use of these complexes in organic field-effect transistors.

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A series of 7 cerium double-decker complexes with various tetrapyrrole ligands including porphyrinates, phthalocyaninates, and 2,3-naphthalocyaninates have been prepared by previously described methodologies and characterized with elemental analysis and a range of spectroscopic methods. The molecular structures of two heteroleptic [(na)phthalocyaninato](porphyrinato) complexes have also been determined by X-ray diffraction analysis which exhibit a slightly distorted square antiprismatic geometry with two domed ligands. Having a range of tetrapyrrole ligands with very different electronic properties, these compounds have been systematically investigated for the effects of ligands on the valence of the cerium center. On the basis of the spectroscopic (UV-vis, near-IR, IR, and Raman), electrochemical, and structural data of these compounds and compared with those of the other rare earth(III) counterparts reported earlier, it has been found that the cerium center adopts an intermediate valence in these complexes. It assumes a virtually trivalent state in cerium bis(tetra-tert-butylnaphthalocyaninate) as a result of the two electron rich naphthalocyaninato ligands, which facilitate the delocalization of electron from the ligands to the metal center. For the rest of the cerium double-deckers, the cerium center is predominantly tetravalent. The valences (3.59-3.68) have been quantified according to their L(III)-edge X-ray absorption near-edge structure (XANES) profiles.