Robert S. H. Liu

Nature of supramolecular complexes controlled by the structure of the guest molecules: formation of octa acid based capsuleplex and cavitandplex.

Factors that govern inclusion of organic molecules within octa acid (OA), a synthetic deep cavity cavitand, have been delineated by examining the complexation behavior of a number of organic molecules with varying dimensions and functionalities with OA. The formation of two types of complexes has been noted: the one which we call cavitandplex is a partially open complex in which a part of the guest molecule remains exposed to water, and the other termed capsuleplex is formed through assembly of two OA molecules. In capsuleplex, the guest is protected from water. Generally, guest molecules that possess ionic head groups form cavitandplex, and all others form capsuleplex. Capsuleplex may contain one or two guest molecules within the capsule. Small organic molecules (<10 A in length) may form both 2:1 and 2:2 capsuleplex, while longer ones (>12 A) preferentially form 2:1 capsuleplex. Extensive 1H NMR experiments have been carried out to characterize host-guest complexes. In the absence of the guest, OA tends to aggregate in water. The extent of aggregation depends on the concentration of OA and the presence of salts in solution. We expect the information obtained from this study to be of great value in predicting the nature of complexes with a given guest and facilitating appropriate guest chosen by researchers.

Azulene-containing donor-acceptor compounds as second-order nonlinear chromophores

Abstract Several novel, thermally stable azulene-containing donor-acceptor molecules were synthesized and their second-order nonlinear optical properties determined by the EFISH method. The βμ-values for these new compounds featuring azulene as the pi-electron donor were comparable with NLO compounds containing para-N,N-diethylaniline as the electron-donor.

Optical power limiting in some azulenic compounds

A series of azulenic compounds are synthesized and their third-order nonlinear optical properties are determined. The compounds are studied in solution using degenerate four wave mixing and z-scan at 532 nm with 30 ps pulses. Extrapolated values for the third-order nonlinear optical susceptibility (chi) (3) of the compounds are in the range 10-9 to 10-8 esu. Z-scan results indicate reverse saturable absorption. Optical power limiting with a f/5 system is demonstrated for all of the compounds studied.

Third-order nonlinear optics of some azulenic donor-acceptor compounds

We studied the third-order nonlinear optical properties of five azulenic donor-acceptor compounds. The compounds were studied in solution in Tetrahydrofuran using backward degenerate four-wave mixing and Z-scan with 30 picosecond pulses at 532 manometer wavelength. Extrapolated values for the third-order nonlinear optical susceptibility ((chi) (3)) of the solute molecules were obtained from concentration dependent measurements. The compounds possess large values of (chi) (3) in the range 3 X 10-10 esu to 3 X 10-8 esu. The two orders of magnitude change in the magnitude of the susceptibility that we observe for this series of donor-acceptor azulenic compounds makes them interesting candidates for the study of structure property relationships in nonlinear optical chromophores. The compounds also exhibit large solvatochromism and may also prove to be useful in second-order nonlinear optical applications.