The Molecular Design Investigations On Several Kinds Of Two-photon Absorption Materials

Two-photon absorption response can be applied in many high-tech fields. Design and synthesis of materials with large two-photon absorption cross section is the important basis of its development. In this thesis, in order to design and select organic materials with large two-photon absorption response, we have performed systematic theoretical research of various organic materials. The density functional theory (DFT) has been applied to optimize the molecular equilibrium geometries. On the basis of the optimized structures, one- and two-photon absorption properties are obtained by ZINDO method combined sum-over-states (SOS) expression and self-compiled program. We have designed some unknown compounds using the same method so as to provide a theoretical basis of synthesizing novel materials with large two-photon absorption cross section. The following is the main content:1. The equilibrium geometries, electronic structures, one- and two-photon absorption properties for two series of linear molecules have been studied. The calculated results show that the maximum one-photon absorption (OPA) wavelength is increased with the stronger electron-donating or electron-accepting capability of the terminal substituent groups. Meanwhile, the maximum two-photon absorption (TPA) cross section values are obviously increased with the increased conjugation length and the stronger electron-donating or electron-accepting capability of the terminal substituent groups.2. The equilibrium geometries, electronic structures, one- and two-photon absorption properties for two series of bis(styryl)benzene molecules have been studied. The calculated results show that increasing the molecular dimension is a very effective method to enhance the values of the two-photon absorption (TPA) cross section. In addition, the intramolecular charge transfer is also a factor for the enhancement of the TPA efficiency.3. Two series of pseudo-octupolar molecules and a dipolar molecule have been investigated. The calculated results show that the two-photon absorption (TPA) cross section values are increased with the increased conjugation length and the stronger electron-donating or electron-accepting capability of the terminal substituent groups. Compared with the dipolar molecule, the pseudo-octupolar molecules have high transparency and larger TPA cross sections, which are promising TPA materials.4. The equilibrium geometries, electronic structures, one- and two-photon absorption properties for two series of three-branched molecules possessing different center have been studied. The calculated results show that the maximum one-photon absorption (OPA) intensities and the maximum two-photon absorption (TPA) cross sections values are gradually increased with the stronger electron-donating or electron-accepting capability of the terminal substituent groups. In addition, intramolecular charge transfer plays a very important role on the TPA.5. Three molecules possessing different center and terminal substituent groups have been investigated. Observing the two molecules with N(CH3)2 peripheral group, the maximum two-photon absorption cross sectionδmax of the molecule with boron (B) center is larger than that of the molecule with nitrogen (N) center. Comparing the two molecules with N center, theδmax is obviously increased with the change from N(CH3)2 to CN group. This indicates that the large intramolecular charge transfer is in favor of the TPA response.