The structural investigation of thin films of two thiophene/fluorene based oligomers was performed using X-ray diffraction analysis, molecular modelling calculations including packing energy minimisation and fluorescence optical microscopy. Single molecule layers, double layers, and blended films of thickness ranging from 3 to 50 nm, of component ratio varying from 0.5 to 50%, were prepared by both ultra high vacuum (UHV) evaporation and co-evaporation, and were compared with spin-coated films of two components with comparable concentration and thickness. The growth develops by islands allowing for a complete phase micro-segregation both in spin coating and in UHV evaporated films. Average crystal size is compatible with a large number of micro-interfaces of two oligomers, thus yielding an efficient energy transfer from the high energy absorbing molecule to the low energy absorbing one. (C) 2004 Elsevier B.V. All rights reserved.