The Effect Of Substituents On The Second-order Nonlinear Optical Properties Of Binaphthyl Bridged Chiral Bis-porphyrins

For the past few years, with the development of photo-communication, photoelectronics and optical information processing. Non Linear Optics (NLO) become more and more important. And because of some disadvantages of inorganic NLO, more and nore people Divert their attention to organic NLO. Compared with the inorganic NLO matertial, organic NLO material can be modified and processed easily, fast response time, and high damage threshold. It has comprehensive application foreground and spread value. How to improve the NLO of organic chromophore is the most important thing. Among the NLO chromophores, because of the conjugate structure's adaptable, porphyrin have excellent NLO property. With natural noncentrosymmetrical structure and intrinsical thermostability, chiral molecules have many unique advantages for NLO materials.In this paper, we studied the second-order NLO properties of some porphyrins, especially the chiral bis-porphyrins. By changing the position of Donor and Accepter electron groups, and using the exciton coupled theory to study the relationship between the second NLO properity and spatial structure. Quantum chemical software Gaussian 03 was employed in calculation, and structures of all molecules were optimized based on the methods of semiempirical B3LYP(DFT) at 6-31G(d,p) basis set level, after which the electronic spectra were calculated by the method of ZINDO. The transition electric dipole moments between ground and excited states, between excited and excited states, the transition energies, the corresponding oscillator strength. Using the SOS program, we calculate the second NLO coefficient, calculated the first hyperpolarizabilitiesβof a series of molecules ,βμ,βHRS, and so on. Finally, we calculated the△μof 1b molecule using the Hyperchem and finite field method, and both of this two methods is correct.Results showed that there were strong exciton coupling interactions between two porphyrin chromophores in these bis-porphyrins, and the Davydov splitting of B bands were related to both distances and relative orientations between two porphyrin rings. The first hyperpolarizabilities of chiral bis-porphyrins depend on the spacial arrangement of the substituents. The increasement of first hyperpolarizabilities in bis-porphyrins is not just related to the increasing of transition dipole moment changes between excited and ground state, but related to the relative orientations between ground state dipole moment vectors and exciton coupling dipole moment vectors as well. For the binaphthyl bridged bis-porphyrins, the second-order nonlinear optical properties could be greatly improved by introducing push-pull substituents on porphyrin chromophore, and it's more than an order of IIb series molecules. the first-order hyperpolarizability of IIc molecules have the same evolution of IIb series molecules. Which can be explained by the excition model. The introduction of acetylene-based made the distance between the monomer porphyrin ring centers decreased, And with the distance between the two neighboring porphyrin ring decreased, appeared a charge transfer transition state (CT state) between the two neighboring porphyrin ring of IIc2 molecule. Transition three-level model channel analysis showed that three-level dipole coupled with enhanced not only with the B exciton transition state, but also closely related with the CT state. It can be improving second-order nonlinear optical properties by optimization of porphyrin dimer dipole orientation and dipole coupling effect.