Theoretical Investigation On Several Organic Two-photon Absorption Materials

Novel two-photon absorption (TPA) materials have attracted increasing interest in recent years due to their potential applications in many different fields such as chemistry, physics and biology. Up to now, the practical TPA materials are still limited, further exploring and researching on new materials with potential TPA properties are urgent. In this thesis, several organic TPA materials have been systematic theoretical investigated. The density functional theory has been used to optimize the geometrical structure. On the basis of the equilibrium geometries, the one- and two-photon absorption properties have been calculated by ZINDO program combine SOS equation and self-compiled FTRNLO program. Then, the internal relations between molecular structure and one- and two-photon absorption properties have been revealed. These investigations will provide some useful and valuable information for designing and synthesizing novel TPA materials with large TPA cross-section values.1. The investigation on the perylene tetracarboxylic derivatives (PTCDs) reveal that increasing the number of naphthalene nucleus, extending the conjugated length on long axis, increasing the strength of donor group on lateral side, and keeping the conjugation effect and inductive effect along the same molecular axis are the efficient ways to enlarge TPA cross-section of PTCDs.The formula of predicting the maximum TPA cross-section of PTCDs compounds are obtained by the relationship between the maximum TPA cross-section and the number of naphthalene nucleus on long axis or number of biphenyl on short axis. PTCDs exibit extremly large TPA cross-section and they are promising TPA materials. 2. A series of pyrene derivatives have been theoretically studied. Results show that pyrene derivatives exhibit extremely large TPA cross-sections and present strong OPA around 400 nm, which indicate that introducing donor groups to pyrene molecule, increasing the number of donor groups, extending the conjugated length, or forming circular conjugated dimmer are all efficient ways to enlarge TPA cross-sections. All these results give us some basic principles to design pyrene derivatives with large TPA cross-sections. This shed light into the significance of the pyrene derivatives as promising fluorescent probes in biochemistry when it was linked to some special recognizing groups.3. The solvent effect on DCM derivatives have been studied. Results show that increasing the number of branches in DCM molecules and introducing stronger electron withdrawing groups are efficient ways to enhance the TPA cross-sections. Investigations on the solvent effects reveal that TPA cross-section increases as the polarity of the solvents increases and it reaches the maximum when the dielectric constantεequal to 20.7. ICT show regular changes which are in agreement with the changing trend of the TPA cross sections, and the products of transition dipole moments andΔQ are all linearly proportional to the TPA cross-sections.4. A series of magnesium ion (Mg2+) selective fluorescent probes based on benzo[h]chromene derivatives have been theoretically studied. Results show that all the studied probe molecules exhibit large TPA cross-sections in response to Mg2+ in 700-1200 nm range. The TPA cross-sections can be greatly enhanced by introducing acceptor groups to the lateral side of benzo[h]chromene, and that probes with stronger acceptor group show larger TPA cross-sections and result in 70-fold enhancing when coordinate with Mg2+. These results shed light into the design strategy of efficient TP fluorescent probes with large TPA cross-sections for Mg2+ sensing in living systems.