Structural dependences of the η6 complexes of 3-amino-9-ethylcarbazole with chromium tricarbonyl fragment on third-order optical nonlinearities

Degenerate four-wave mixing measurements, using the 35 ps pulses at 532 nm, have been employed to investigate the third-order nonlinear optical parameters of two chromium tricarbonyl complexes η 6-bonded to 3-amino-9-ethylcarbazole at either the NH2-substituted aryl ring (1) or the unsubstituted ring (2) and their precursor 3-amino-9-ethylcarbazole (AECz). The second-order hyperpolarizability Y of the compounds 1 and 2 were found to be 42.9×10 31 and 35.9×10 31 esu, respectively, approximately one order of magnitude greater than AECz. The relation between the molecular structure and second-order hyperpolarizability of the compounds 1 and 2 was explored in detail based on the three-level model and the density functional theory (DFT) calculation. The theoretical results indicate that the spatial distribution of electron density has the profound role in the third-order nonlinear optical properties. Supported by the National Natural Science Foundation of China (Grant No. 10574046), National Key Project for Basic Research of China (Grant Nos. 2006CB806006 and 2006CB921105), Program for Changjiang Scholars and Innovative Research Team in University (PCSIRT), Program for New Century Excellent Talents in University (NCET-04-0420), the Doctoral Program of High Education (Grant No. 20050269011), Phosphor Program Sponsored by Shanghai Science and Technology Committee (Grant No. 06QH14003)