Abstract: In order to study the third-order nonlinear optical properties of porphyrin, the nonlinear refractive indexes of two kinds of chiral zinc porphyrin complexes Zn(o-BocTyr)TAPP(host 1) and Zn(p-BocTyr)TAPP(host 2) were measured with nanosecond laser pulses at 532 nm by Z-scan techniques. And then, molecular recognition was studied between hosts and imidazole (Im) derivatives. The conformational searching of chiral zinc porphyrins with imidazole derivatives was studied by simulated annealing method on the basis of Tripos force field. The results illuminate:(1) these compounds showed very strong reverse saturable absorption and self-defocusing effect, (2) because of the different positions of the side chain, hosts had different polarized degrees, host 1 gave the larger nonlinear refractive index n2(－9.85×10-9 esu), (3) the aryl-aryl stacking interaction existed between the phenyl ring in side chain and porphyrin plane, (4) the coordinated orientation in which imidazole and 2-methylimidazole (2-MeIm) reacted to host 1 were studied. Imidazole coordinated to host 1 from the side with latral chain because the conformation had the lower energy, 2-methylimidazole coordinated to host 1 from the side without lateral chain, but host 2 had no coordination selectivity. The molecular recognition of this host and guest system was calculated by quantum chemistry. Experimental essence was further discussed by theoretical calculation.

Key words: Nonlinear optical properties, Z-scan, Chiral zinc porphyrin molecular recognition, Conformation study, Quantum chemistry