Subphthalocyanine Fused Dimer and Subphthalocyanines Conjugates

An approach for employing SubPcs and SubPc fused dimers [1] as active units in molecular recognition of fullerenes and artificial photosynthetic systems has been developed. Thus, the preparation of multi-SubPc systems constituted by SubPc and SubPc fused dimer units connected by their mutual axial positions has been explored. For this purpose, a series of SubPcs and SubPc dimers bearing different conjugated spacers linked by alkyne bonds to the SubPc or SubPc dimer boron atoms have been synthesized. Two multi-SubPc hybrids comprised of a perfluorinated SubPc fused dimer (syn or anti topoisomer) axially functionalized with unsymmetrical octylthio-substituted SubPcs linked through their periphery by ethynyl linkers to the boron atoms of the dimer have been prepared. Electrochemical and steady state photophysical studies of the syn- hybrid suggest the existence of an electron transfer process from SubPc units to photoexcited SubPc dimer to generate a (SubPc•+-SubPc Dimer•-) radical pair. Furthermore, the position that the two axial SubPc units acquire in this assembly gives rise to unique supramolecular recognition sites suitable for the complexation of fullerenes. Thus, the binding ability of this hybrid towards different fullerene derivatives, namely C60 , C70 , C60-PCBM and C70-PCBM, has been analyzed through UV-vis absorption, fluorescence and NMR titrations. It has been demonstrated that syn-compounds display a unique fullerene complexation mode. Initially, the formation of a 1:1 supramolecular complex, where the axial octylthio-substituted SubPcs embraces a guest molecule with remarkable association constants of around 106 - 104 M-1, is observed. The spatially-defined cavity generated by the rigid and short alkynyl linkers shows a higher affinity for the bigger fullerene derivatives. Then, a secondary supramolecular interaction between the perfluorinated SubPc syn dimer unit and another fullerene molecule has been detected and quantified, with significant binding constants of 104-103 M-1 that depend on the size and the host-guest electrostatic interactions, leading to the formation of the final 1:2 supramolecular ensemble [2]. [1] C. G. Claessens, D. González-Rodríguez, M. S. Rodríguez-Morgade, A. Medina, T. Torres, Chem. Rev. 2014, 114, 2192–2277. [2] G. Zango, V. Mariñas, M. V. Martínez-Díaz, D. Guldi, T. Torres, in preparation