Molecular stacking and emission properties in Langmuir-Blodgett films of two alkyl substituted perylene tetracarboxylic diimides

The structural and optical properties of Langmuir-Blodgett (LB) films of two perylene diimide derivates, N,N'-Bis(propyl)-3,4,9,10-perylenebis(dicarboximide) and N,N'-Bis(neopentyl)-3,4,9,10-perylenebis(dicarboximide), are reported. The surface pressure-area (pi-A) isotherms have evidenced how the lateral chain substituents control the strength of the intermolecular interaction. Nevertheless, a head-on tilted molecular orientation on the water subphase was found for both compounds. This molecular orientation is preserved when the monolayers are transferred onto substrates. Molecular orientation in the films was extracted from comparative analysis of transmission and reflection-absorption infrared spectroscopy (RAIRS) data. Film structure has been studied by means of atomic force microscopy (AFM). The observed different emission profiles have been correlated with the ability of the derivatives to get coupled. (C) 2003 Elsevier B.V. All rights reserved.