Suppression of chromophore coupling in thin films by chemical substitutionof a perylene tetracarboxylic acid diimide

Thin films (1-100 nm) of 1,6,7,12-tetrachloro-N,N'-dimethyl perylene tetrac arboxylic acid diimide (Cl4MePTCDI) were prepared on glass and quartz subst rates by drop coating from solution and by physical vapor deposition under variation of substrate temperature and deposition rate. Optical absorption spectra were measured in situ in dependence on average film thickness durin g film growth under variation of deposition rate and substrate temperature and following film preparation ex situ in dependence on sample temperature. The results are compared to those obtained earlier [ J. Phys. Chem., B 199 9, 103, 3078] at thin films of unsubstituted N,N'-dimethyl perylene tetraca rboxylic acid diimide (MePTCDI). In contrast to unsubstituted MePTCDI no si gnificant chromophore coupling could be detected in films of Cl4MePTCDI. A relative high optical emission signal for thin films of Cl4MePTCDI with cha racteristics quite similar to the solution spectrum clearly confirmed this interpretation. A twisted structure of the molecule as indicated earlier [J . Phys. Chem., 1992, 96, 7988] is discussed as the basis of changes in the solid state structure relative to unsubstituted MePTCDI which has a planar aromatic system and grows in crystalline films, (C) 2000 Elsevier Science S .A. All rights reserved.