Organic, Polymer and Organometallic Chemistry; Asymmetric Catalysis; Chiral Sensors; Optically Active Materials
Multi-disciplinary research programs involving organic synthesis, polymer chemistry, dendrimers, organometallic chemistry, asymmetric catalysis, and molecular recognition are conducted in our laboratory. Our main interests focus on the design and synthesis of novel chiral molecules and macromolecules for applications in asymmetric catalysis, chiral sensors, polarized light emission and nonlinear optics.
We have chosen the derivatives of (R)- and (S)-1,1′-bi-2-naphthol (BINOL) to build novel main chain chiral conjugated polymers since these molecules have exhibited remarkably stable chiral configuration as well as high chiral induction in many asymmetric processes. We expect that incorporation of the optically active binaphthyls in the main chain of conjugated polymers may lead to efficient and stable chiral induction or chiral discrimination when these materials are used to carry out asymmetric electrosynthesis, polarized light emission and other applications. Efficient electroluminescent properties have been observed for these materials. Chiral conjugated nonlinear optical polymers are also synthesized and studied.
We have discovered that the Lewis acid complexes of the optically active binaphthyl molecules and polymers can carry out highly enantioselective organic reactions such as organozinc additions to aldehydes, hetero-Diels-Alder reactions, 1,3-dipolar cycloadditions, reductions of ketones, Michael additions, epoxidations, and others. Using the chiral polymers has the advantage of easy recovery of the catalysts and simplified product purification. We have further synthesized optically active polymers that contain both BINOL and BINAP ligands. The BINOL ligands are used to make Lewis acid catalysts and the BINAP ligands are used to make late transition metal catalysts. Such novel multifunctional chiral catalysts have been used to catalyze tandem asymmetric reactions with high enantioselectivity as well as diastereoselectivity.
We have synthesized novel rigid and optically active dendrimers. Efficient energy migration from the cross-conjugated light harvesting dendrons to the chiral binaphthyl core has been observed. The fluorescence intensity of these dendrimers is dramatically increased over that of the small parent molecule BINOL. The greatly enhanced fluorescence of the dendrimers makes them more useful as fluorescent sensors than BINOL. We have discovered that the fluorescence of the dendrimers can be enantioselectively quenched by chiral amino alcohols. Thus, the dendrimers can serve as highly sensitive as well as enantioselective fluorescent sensors. Enantioselective hosts for the fluorescent detection of other chiral organic molecules such as a-hydroxycarboxylic acids have also been designed and synthesized. Further study of these materials aims at developing enantioselective fluorescent sensors for rapid determination of the enantiomeric composition of chiral compounds. One application of such sensors will be in the combinatorial search of chiral catalysts.
Simultaneous determination of both the enantiomeric composition and concentration of a chiral substrate with one fluorescent sensor. Yu S, Plunkett W, Kim M, Pu L. J Am Chem Soc. 134:20282-5 (2012).
A novel near-infrared fluorescence imaging probe for in vivo neutrophil tracking. Xiao L, Zhang Y, Berr SS, Chordia MD, Pramoonjago P, Pu L, Pan D. Mol Imaging. 11:372-82 (2012).
Optical properties of solution-processable semiconducting TiOx thin films for solar cell and other applications. Li J, DeBerardinis AM, Pu L, Gupta MC. Appl Opt. 51:1131-6 (2012).
Characterization of novel synthesized small molecular compounds against non-small cell lung cancer. Zhao Y, Turlington M, LaPar DJ, Jones DR, Harris DA, Kron IL, Pu L, Lau CL. Ann Thorac Surg. 92:1031-7 (2011).
Enantioselective fluorescent sensors: a tale of BINOL. Pu L. Acc Chem Res. 45:150-63 (2012).