Supramolecular structures and photoelectronic properties of the inclusion complex of a cyclic free-base porphyrin dimer and C60

Abstract

A cyclic free-base porphyrin dimer H4-CPDPy (CPD = cyclic porphyrin dimer) linked by butadiyne moieties bearing 4-pyridyl groups self-assembles to form a novel porphyrin nanotube in the crystalline state. The cyclic molecules link together through nonclassical C-H···N hydrogen bonds and π-π interactions of the pyridyl groups along the crystallographic a axis. H4-CPDPy includes a C 60 molecule in its cavity in solution. In the crystal structure of the inclusion complex (C60⊂H4-CPDPy), the dimer "bites" a C60 molecule by tilting the porphyrin rings with respect to each other, and there are strong π-π interactions between the porphyrin rings and C60. The included C60 molecules form a zigzag chain along the crystallographic b axis through van der Waals contacts with each other. Femtosecond laser flash photolysis of C 60⊂H4-CPDPy in the solid state with photoexcitation at 420 nm shows the formation of a completely charge-separated state {H4-CPDPy •+ + C60 •-}, which decays with a lifetime of 470 ps to the ground state. The charge-carrier mobility of the single crystal of C60⊂H 4-CPDPy was determined by flash photolysis time-resolved microwave conductivity (FP-TRMC) measurements. C60cH 4-CPDPy has an anisotropic charge mobility (σμ = 0.16 and 0.13cm 2V-1s-1) along the zigzag chain of C60 (which runs at 45° and parallel to the crystallographic b axis). To construct a photoelectrochemical cell, C60⊂H 4-CPDPy was deposited onto nanostructured SnO2 films on a transparent electrode. The solar cell exhibited photovoltaic activity with an incident photon to current conversion efficiency of 17 %. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.