Self-organization of crystalline domains in originally amorphous perylene diimide films

Thin films (100-150 nm) of 1,6,7,10-tetra-chloro-N, N'-dimethyl-perylene-tetracarboxylic bisimide (Cl(4)MePTCDI) were grown by physical vapour deposition on glass and characterized as being widely amorphous with a rather small degree of intermolecular electronic coupling. A slow reorganization process was detected upon conditioning the films in air by optical microscopy. Polarized microscopy and scanning force microscopy revealed the formation of crystalline domains. Locally resolved absorption and photoluminescence measurements were used to analyse changes in intermolecular coupling. Individual domains were studied by micro-photoluminescence and temperature-dependent photoluminescence was used to characterize the degree of intermolecular coupling in the crystalline domains. The results are discussed in view of recently proposed applications of such perylene imides with a twisted aromatic core in organic inverters and organic photovoltaic cells.