We present a comprehensive experimental and theoretical study of the optical properties of matrix-isolated molecules of the two perylene derivatives N , NЈ-dimethylperylene-3,4,9,10-dicarboximide ͑MePTCDI͒ and 3,4,9,10-perylenetetracarboxylic dianhydride ͑PTCDA͒. A solid solution of the dyes in an SiO 2 matrix exhibits monomer-like behavior. Transient absorption pump-probe spectroscopy in the range 1.2-2.6 eV has been performed on an ultrafast time scale. The differential transmittance reveals contributions from ground-state bleaching, stimulated emission, and excited-state absorption. Both systems exhibit broad excited-state absorption features below 2.0 eV with a clear peak around 1.8 eV. The spectra can be consistently explained by the results of quantum-chemical calculations. We have applied both the coupled cluster singles and doubles ͑CCSD͒ model and the multireference-determinant single and double configuration-interaction ͑MRD-CI͒ technique on the basis of the intermediate neglect of differential overlap ͑INDO͒ Hamiltonian. The results are insensitive to whether the geometry is optimized for the electronic ground state or first excited state. The experimental polarization anisotropies for the two major transitions are in agreement with the calculated polarizations.
Thin vacuum deposited films of aluminum tris(8-hydroxyquinolinate) (Alq3) embedded in SiO2 matrix at concentrations corresponding to a single-molecule distribution are investigated. The spectral properties of the films are studied by luminescence spectroscopy. It is established that the dilution of Alq3 in the matrix leads to blueshift of the luminescence maximum up to 0.28eV compared to pure Alq3 layers. In contrast to the recently reported facial isomer of Alq3 in the crystalline δ phase, we conclude from our spectral data the observation of facial isomer molecules.
In this chapter we describe the preparation of polyimide thin films by physical vapour deposition and comment on their potential application as a pure material or a thin layer matrix for producing nanocomposite layers. Their superb properties, such as a low dielectric constant, high thermal-and photo-stability, high chemical resistance and high optical transmittance predetermine their wide-spread applications as a casts and layers used as insulators, protective or capsulation layers, mechanical or diffusion barriers, in opto-and microelectronics. The bulk properties of the polyimide allowed the preparation of nanocomposite materials with organic chromophores as a "guest" (the embedded in the matrix nanosized particles). Moreover, some of the "guest" could bind to the polyimide chain. There are numbers of aromatic polyimides which are broadly used as thin layers in nanotechnology. Vapour deposition of the precursors and solid state reactions of imidization are of a greater priority than the spin coating and dipping methods. These as-deposited films by the vacuum deposition process consist of a dianhydride and diamine mixture, which by solid state reactions is converted to polyimide by thermal treatments or by combined microwave and thermal treatments. The physical vapour deposition as a "dry" method provides high purity for producing thin polymer films of controlled thickness, ratio of precursors and composition control of the so prepared layers. In this chapter we suggest possibilities for the practical application of vapour deposition of precursors and the following solid state reactions. By the used spectral method-Fourier Transform Infrared Spectroscopy for analysis of the investigated kinetics of imidization reactions and microstructure of the layers are studied. The relationship between vapour deposition conditions and the presence of regular chains leading to the appearance of infrared bands is discussed. Polymers are also capable of forming a range of conformations depending on the backbone structure. The conditions for preparation by physical vapour deposition and solid state reaction of polyimide or nanocomposite polyimide layers are discussed.
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