Near infra-red emission of charge-transfer complexes of porphyrin–fullerene films

Solid porphyrin–fullerene films were prepared by evaporating a mixture of porphyrin and fullerene in solution and by deposition of Langmuir–Blodgett films where the dyes were covalently linked to each other. Both types of the films exhibited an emission band shifted to the near infrared region, ca. 800 nm, where neither porphyrin nor fullerene emits alone nor mixed in solution. The emission is attributed to an emitting charge transfer (CT) state formed by porphyrin and fullerene moieties. It is characterized by a long lifetime, ca. 2 ns, and high quantum yield, 0.14%. Remarkably small total reorganization energies, less than 0.2 eV, are deduced from the CT emission spectra of the porphyrin–fullerene films.