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Abstract This thesis represents a theoretical and experimental study for physical properties of some organic compounds. This thesis consists of four chapters, conclusion and list of references. The thesis begins with a short theoretical background about the field of computational physics, starting from the basic many-body problems to the Hartree-Fock (HF) and density functional theory (DFT). The Gaussian 03W and Gauss view (4.1) program package, basis sets, origin of molecular vibrations and IR spectroscopy. We also represent the theory of light absorption, UV/Vis spectroscopy, theory of charge transport process in organic semiconductors and finally the theory of organic photovoltaic solar cell. Then it represented a brief overview of the experimental techniques used in this thesis. It describes the basic of the conventional thermal evaporation (vacuum deposition) techniques, the configuration of the sample preparation, the film thickness measurement methods, the techniques that used to determine the molecular structure, i.e. proton nuclear magnetic resonance (1H-NMR) measurements, single crystal Xray stereo-diffractometer, X-ray diffraction pattern (XRD) and Fourier transform infrared spectroscopy (FT-IR) techniques, the techniques that used to determine the optical properties usually the spectrophotometric measurement of transmittance (T) and reflectance (R) at normal incidence of light and also the techniques that used to determine the electrical properties. The results of a computational study for the molecular structure of 2-(2-furanylmethylene) propanedinitrile (FMN) and its electrical properties are also represented. The equilibrium geometries, harmonic vibrational frequencies, thermo-chemical parameters, total dipole moment and HOMO-LUMO energies are calculated by HF utilizing 6- 31G and 6-311G basis sets and DFT/B3LYP utilizing 6-31G and 6- 31lG basis sets. Comparison of the vibrational frequencies calculated at B3LYP utilizing 6-31G and 6-311G basis sets with experimental values reveals that B3LYP/6-311G gives reasonable deviations from the experimental values. The results showed that 2-(2-furanylmethylene) propanedinitrile possesses a dipole moment of 7.5 Debye and HOMOLUMO energy gap of 3.92 eV. The electrical properties of 2-(2- furanylmethylene) propanedinitrile thin film is investigated by studying the dark and illumination (J-V) characterization of Au/FMN/p-Si/Al heterojunction. The transport mechanism of the electronic charges are determined for the heterojunction in the forward and reverse directions in Au/FMN/p-Si/Al heterojunction. Results showed that the RR was about 2.9 for room temperature. The determined values of Rs and Rsh are found to be 0.48 KΩ and 4.85 KΩ, respectively. At low forward voltages the transport mechanism is tunneling mechanism and at high voltage is space-charge-limited conduction (SCLC) mechanism. In the low voltage range, the current is due to thermally generated carriers, while in the higher voltage range a bulk limited conduction process is the dominated mechanism. The junction shows a photovoltaic behavior with a maximum open-circuit voltage, 𝑉𝑜𝑐, of 0.19 V and a short-circuit current density, 𝐽𝑠𝑐, of 102.7 mA/m2. Finally the thesis represent an experimental study of XRD pattern of 2-chloro-5-(2,5-dimethoxy-benzylidene)-1,3-diethyl-dihydropyrimidine- 4,6(1H,5H)-dione, a combined experimental and computational study for the molecular structure and vibra frequencies of the investigated compound. The equilibrium geometries, harmonic vibrational frequencies, thermo-chemical parameters, total dipole moment and HOMO-LUMO energies are calculated by DFT/B3LYP utilizing 6-31G and 6-31lG basis sets. Our calculated results have showed that 2-chloro-5-(2,5-dimethoxy-benzylidene)-1,3- diethyl-dihydro-pyrimidine-4,6(1H,5H)-dione possesses a dipole moment of 4.9 Debye and HOMO-LUMO energy gap of 3 eV. We also represent the optical properties of 2-chloro-5-(2,5- dimethoxy-benzylidene)-1,3-diethyl-dihydro-pyrimidine-4,6(1H,5H)- dione: transmittance (T), reflectance (R), optical constants (n,k), absorption coefficient (𝛼), molar extinction coefficient (𝜀𝑚𝑜𝑙𝑎𝑟), oscillator strength (𝑓), electric dipole strength (𝑞2), energy gap (𝐸𝑔), single oscillator energy (𝐸0), dispersion energy (𝐸𝑑) and dielectric constant (𝜀𝐿). X-ray diffraction results indicate that powder of the investigated compound has a polycrystalline nature with a monoclinic structure. Effect of annealing on the optical properties was investigated. The values of the energy band gap are calculated using an optical method. The type of the optical transition responsible for the optical absorption is direct allowed transition. The refractive index showed an anomalous dispersion in the absorption region as well as a normal one in the transparent region. The dispersion parameters of 2-chloro-5-(2,5- dimethoxy-benzylidene)-1,3-diethyl-dihydro-pyrimidine-4,6(1H,5H)- dione films are determined and they are affected by annealing effect |