Excited state structural dynamics and Herzberg-Teller coupling of tetraphenylporphine explored via resonance Raman spectroscopy and density functional theory calculation.
ABSTRACT Resonance Raman spectra of free-base tetraphenylporphine (TPP) were obtained with 397.9, 416, and 435.7nm excitation wavelengths and density functional calculations were done to elucidate the electronic transitions and the resonance Raman spectra (RRs) of TPP. The RRs indicate that the Franck-Condon region photodynamics for S(0)-->S(4) electronic state is predominantly along the C(m)-ph stretch while that for S(0)-->S(3) electronic state is predominantly along the porphin ring C(beta)C(beta) stretch. Non-totally symmetric vibrational modes were regularly presented in resonance Raman spectra: the shorter the excitation wavelengths were, the stronger intensity the modes had, which can be interpreted in terms of electric dipole transition moments caused by Franck-Condon and Herzberg-Teller coupling. Four non-total symmetry vibrational mode upsilon(52,)upsilon(64), upsilon(97) and upsilon(130) in A(2) irreducible representative of TPP were observed in 397.9, 416 and 435.7nm resonance Raman spectrum. With the shorter wavelength laser excitations at 416 or 397.9nm, the A(2) vibrational modes show more enhanced Raman intensity by comparison with those in the TPP spectrum excited at 435.7nm.
- [show abstract] [hide abstract]
ABSTRACT: Hydrogenated amorphous silicon-nitrogen (a-Si<sub>1-x</sub>N<sub>x </sub>:H) thin films are interesting for optoelectronic applications. The optical gap of this material varies in the range from 1.8 to 3 eV depending mainly on the nitrogen content. The electronic, optical and structural properties are influenced by the technological parameters. The authors deposited hydrogenated amorphous silicon-nitrogen thin films by the use of Plasma Enhanced Chemical Vapour Deposition (PECVD). The system consisted of an ultra high vacuum chamber equipped with 13.56 MHz RF generator, separate gas lines with gas flow meters, turbomolecular pumps with automatic pressure control and a precise temperature regulator. It was possible to obtain 10×10 cm<sup>2</sup> homogeneous films with reproducible properties in a silane-ammonia gas mixture, Optical, structural, chemical composition and electrical properties of a-Si<sub>(1-x)</sub>N<sub>x</sub>:H were examined by optical and infrared spectroscopy, conductivity and photoconductivity measurements. The films revealed the monotonic increase in optical gap value with nitrogen content increase. The nitrogen rich samples exhibit low photoconductivity and a wide bandgap. These materials could substitute for hydrogenated amorphous silicon for such applications as solar cells or photodetectorsWide Bandgap Layers, 2001. Abstract Book. 3rd International Conference on Novel Applications of; 02/2001