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

摘要

Thin films (1-100 nm) of 1,6,7, 12-tetrachloro-N,N'-dimethyl perylene tetracarboxylic acid diimide(Cl_4MePTCDI) were prepared on glass and quartz substrates bydrop coating from solution and by physical vapor depositionunder variation of substrate temperature and deposition rate.Optical absorption spectra were measured in situ in dependenceon average film thickness during film growth under variation ofdeposition rate and substrate temperature and following filmpreparation ex situ in dependence on sample temperature. Theresults are compared to those obtained earlier (J. Phys. Chem., B1999, 103, 3078) at thin films of unsubstituted N, N'-dimethylperylene tetracarboxylic acid diimide (MePTCDI). In contrast tounsubstituted MePTCDI no significant chromophore couplingcould be detected in films of Cl_4MePTCDI. A relative highoptical emission signal for thin films of Cl4MePTCDI withcharacteristics quite similar to the solution spectrum clearlyconfirmed this interpretation. A twisted structure of the moleculeas indicated earlier (J. Phys. Chem., 1992, 96, 7988) is discussedas the basis of changes in the solid state structure relative tounsubstituted MePTCDI which has a planar aromatic system andgrows in crystalline films.