Molecular organization and mixing in thin solid films of novel perylene tetracarboxylic dianhydride derivatives: Infrared and surface enhanced Raman studies

The present work focuses on the fabrication and spectroscopic characterization of submicron thin solid films of novel organic dyes. The synthesis, thin film fabrication, electronic and vibrational spectra of neat materials are described. The main group of organic dyes studied here are novel perylene tetracarboxylic derivatives. The fabrication of thin solid films on a variety of substrates is demonstrated and the long-range molecular organization in the films, extracted using mainly infrared techniques, is illustrated. The starting point in using vibrations as structural probes, is the vibrational assignments of the characteristic perylene tetracarboxylic fundamentals for each dye under study. The assigned vibrational spectra are employed as references to extract the molecular organization in the vacuum evaporated films using data from the complementary techniques: transmission infrared and reflection-absorption infrared spectroscopy. The understanding of the molecular organization opens the door to changing and controlling the molecular film structure with thermal annealing, and these studies are illustrated for bis(n-propylimido) perylene films. It is shown that reorientation can be induced in thin films of bisPTCD dye. The factors that may determine reorientation on thermal annealing are investigated.; Surface-enhanced spectroscopic studies of metal island films coated with the dyes were carried out. The surface-enbanced vibrational spectroscopy (SEVS) used encompasses spectral data obtained from surface-enhanced Raman scattering (SERS), surface-enhanced-resonance Raman scattering- (SERRS) and surface-enhanced infrared (SEIR).; The first systematic study of mixed thin solid films of PTDC materials and phthalocyanines, using vacuum co-evaporation, is presented. Mixed films of Perylene and phthalocyanine derivatives were fabricated and investigated using SERS, SERRS and SERRS imaging. It is demonstrated that SERRS global imaging is a powerful analytical tool that permits one to distinguish the degree of mixing in mixed films using 1 mW of laser power at the sample. For the first time, global images of mixed films consisting of PTCD and ClInPc, ClGaPc, CuPc and CoPc are reported. The point to point mapping and wide field imaging of the mixed films permits chemical imaging that shows the average distribution of both perylene and phthalocyanine derivatives. SERRS studies indicate minimal molecular interaction between the phthalocyanine and perylene constituents of the fabricated mixed films.