The Photophysical Properties Of Metal Phthalocyanine

The synthesis, characterization and the performance optimization of novel materials are quite important to current science and technique development. The optical properties, ultrafast dynamics and third-order optical nonlinearity (3rd NLO) properties of materials are essential to the applications in the fields of photonic information, photo-electronic and health science. Metal-organic materials, such as metallophthalo-cyanines (MPcs), are those with special properties. We studied the properties of MPcs in both experimental and computational aspects, where the experiments carried out were UV-Vis spectra, femtosecond (fs) pump-probe, optical Kerr effect (OKE) and z-scan techniques, and the computational methods introduced were Hartree-Fock (HF), time-dependent density functional theory (TD-DFT), finite-field (FF) and sum-over-states (SOS) procedures. We demonstrate the effects of peripheral substitution, axial substitution, dimerization, polymer-grafting and etc on the UV-vis spectra, ultrafast dynamics and 3rd NLO properties of the materials. The main creative results are the followings:1. The UV-vis spectra demonstrate the effects of peripheral substitutions and etc to the spectra of solution and thin films of MPcs. For the thin films, MPcs tend to form ordered structures with red-shifted and broadened absorption bands, and the intermolecular interactions affect the shape and position of the absorption bands. By introducing the steric hindrance effects of peripheral and axial substitutions, the red-shift and broadening of the bands are weakened as the structure of the thin films become amorphous. By using HF optimization of the MPcs structures, theeffects of central metal, axial substitution and etc are demonstrated, and the TD-DFT calculation well simulates their absorption spectra.2. The ultrafast dynamics obtained from fs pump-probe experiments reveal the decay behaviors of the excitons in the thin films, including the contributions of both bimolecular and unimolecular processes, such as exciton-exciton annihilation (E-EA) and inter-system crossing (ISC), etc. We demonstrate that the structures of MPcs greatly influence these processes, and the careful analyses of the ultrafast dynamics clarify their relationships. Furthermore, both the Frenkel and CT excitons exist in MPcs thin films, and they show different decay behaviors. From the point view of a potential-curve-based model, the difference is that whether they can jump over the intermolecular potential barrier or not, which depends on the intermolecular distance and the excitation photon energy. However, the effects of Frenkel or CT excitons, as well as the intermolecular distance, can be controlled by peripheral substitutions. Furthermore, based on the optimization of the molecular structures of MPcs cations and anions by HF method, and the computation of the excited states by TD-DFT method, the spectra of Frenkel and CT excitons were obtained. The agreement with the experimental data proves that the proposed potential-curve-based model is reasonable.3. The 3rd-NLO properties of materials can be studied by OKE and z-scan experiments as well as the computational methods, such FF and SOS procedures. It is shown that the central metal, dimerization and etc have great impacts on the 3rd-NLO properties of MPcs. For the metals in the same subgroup, it is found that the larger metal atom leads to the stronger 3rd-NLO response, where the relativity effect also took part in. A direct comparison of OKE and pump-probe traces illuminates the contributions ofelectron cloud distortion and excitation states to 3rd-NLO properties, and the polymer-grafting is found having dramatic effects on the electron cloud distortion.In conclusion, we studied the photophysical properties of a kind of metal-organic materials, i.e. metallophthalocyanines, by means of experiments and computations. The research results are very useful for better understanding of the electronic structure of metal-organic materials and the effects of molecular engineering to phthalocyanines, which are essential for the far-ranging applications of phthalocyanine materials.