Supramolecular Structures and Photoelectronic Properties of the Inclusion Complex of a Cyclic Free-Base Porphyrin Dimer and C-60

A cyclic free-base porphyrin dimer H-4-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 non-classical C-H center dot center dot center dot N hydrogen bonds and pi-pi interactions of the pyridyl groups along the crystallographic a axis. H-4-CPDPy includes a C-60 molecule in its cavity in solution. In the crystal structure of the inclusion complex (C-60 subset of H-4-CPDPy), the dimer bites a C-60 molecule by tilting the porphyrin rings with respect to each other, and there are strong pi-pi interactions between the porphyrin rings and C-60. The included C-60 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 subset of H-4-CPDPy in the solid state with photoexcitation at 420 nm shows the formation of a completely charge-separated state {H-4-CPDPy center dot+ + C-60(center dot-)}, which decays with a lifetime of 470 Ps to the ground state. The charge-carrier mobility of the single crystal of C-60 subset of H-4-CPDPy was determined by flash photolysis time-resolved microwave conductivity (FP-TRMC) measurements. C-60 subset of H-4-CPDPy has an anisotropic charge mobility (Sigma mu=0.16 and 0.13 cm(2)V(-1) s(-1)) along the zigzag chain of C-60 (which runs at 45 degrees and parallel to the crystallographic b axis). To construct a photoelectro-chemical cell, C-60 subset of 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%.