Research Interests:
My research is focused on the intersection of organic chemistry and materials science with emphasis on the synthesis and understanding of organic materials with well-controlled electronic and optical properties. Our overarching philosophy is the exploration of the relationships between chemical structure and resulting properties so as to facilitate discovery of new materials for organic solar cells, organic electronics, water splitting, and other practical applications.
Polymer Chemistry
We are especially interested in exploring reactions that require mild reaction conditions for syntheses of functional polymers and materials.
- Palladium-mediated coupling reactions (The Heck reaction, the Stille coupling reaction) for polycondensation;
- Living ring-opening polymerization for the synthesis of biocompatible polyesters;
- Exploring new polycondensation reactions (C-H bond activation reactions) as an alternative method to the Stille reaction;
- Ladder polymer chemistry that allows syntheses of ladder types of heteroacenes and heterohelicenes.
Functional Materials
- Solar cell materials. Our group is engaged in developing low bandgap materials that can efficiently harvest and convert solar energy into electricity. Two types of molecules are being designed and synthesized. a) p-Type low bandgap semiconducting polymers both linear and two-dimensional. b) n-Type semiconductors as electron-acceptors. We are developing state of art materials for both fundamental studies and device optimization. Extensive effort is devoted to the characterization of these new materials with regard to their structural and photophysical properties. In addition to designing functional materials, approaches to optimizing light conversion are pursued through device engineering and the optimization of processing conditions, including plasmonic enhancement of light absorption, nanotubes for increased charge transport, and ternary blend solar cells.
- Chiral polymers and heterohelicenes. This project concerns the effect of chirality of polymers on their properties, such as electron-optic properties and self-assembly.
- Photocatalysts for water splitting based on functional poymers containing metal complexes and nanoporous polymers. In addition to photovoltaics, one approach to convert sunlight into usable forms of energy, is to utilize solar energy to photo-catalytically convert inert chemicals, such as water and carbon dioxide, into energy-rich, storable chemical fuels. Light-induced splitting of water into oxygen and hydrogen is the most attractive approach not only because it can provide one potential solution to the world’s ever-increasing energy demands, but also because the resulting fuel is environmentally benign. Our method toward this goal is the development of photocatalysts based on semiconducting polymers chelated with transition metals. In addition to their photocatalytic effect, we also study other physical properties of polymer metal complexes, such as photorefractive effects, photoconductivity, light emission and novel redox properties. These materials exhibit promising potential for applications in solar energy conversion as photocatalysts for water splitting and carbon dioxide reduction, sensors, polymer-supported electrodes, nonlinear optics, and electroluminescence.
- Materials for molecular electronics. This project explores the power of organic chemistry in designing and synthesizing molecular electronic components, such as molecular diodes, molecular switches, and information storage material. A typical example is the demonstration of edge-on chemical gating effect in molecular wires utilizing the pyridinoparacyclophane moiety as the gate. The results show behavior similar to field-effect transistors. At the same time, protonation/deprotonation of the pyridine ring triggers a reversible alteration of the electrical properties of the molecular wire, leading to a binary on/off switch system.
Another example is the synthesis of molecular diodes consisting of conjugated diblock and demonstration of their rectification effect. These materials present the unlimited opportunity to expand fundamental knowledge of the electronic and structural properties of organic electroactive materials.
Selected References
- Cai, Z.; Lo, W.-Y.; Zheng, T.; Li, L.; Zhang, N.; Hu, Y.; Yu, L. Exceptional Single-Molecule Transport Properties of Ladder-Type Heteroacene Molecular Wires. J. Am. Chem. Soc. 2016, 138, 10630–10635.
- Li, L.; Cai, Z.; Wu, Q.; Lo, W.-Y.; Zhang, N.; Chen, L. X.; Yu, L. Rational Design of Porous Conjugated Polymers and Roles of Residual Palladium for Photocatalytic Hydrogen Production. J. Am. Chem. Soc. 2016, 138, 7681-7686.
- Wu, Q.; Zhao, D.; Schneider, A. M.; Chen, W.; Yu, L. Covalently Bound Clusters of Alpha-substituted PDI—Rival Electron Acceptors to Fullerene for Organic Solar Cells. J. Am. Chem. Soc. 2016, 138, 7248-7251.
- Lo, W.-Y.; Bi, W.; Li, L.; Jung, I. H.; Yu, L. Edge-on Gating Effect in Molecular Wires. Nano Lett. 2015, 15, 958–962
- Lu, L.; Chen, W.; Xu, T.; Yu, L. High-Performance Ternary Blend Polymer Solar Cells Involving Both Energy Transfer and Hole Relay Processes. Nat. Commun. 2015, 6, 7327.
- Lu, L.; Xu, T.; Chen, W.; Landry, E. S.; Yu, L. Ternary Blend Polymer Solar Cells with Enhanced Power Conversion Efficiency. Nat. Photonics 2014, 8, 716–722.
- Carsten, B.; Szarko, J. M.; Son, H. J.; Wang, W.; Lu, L.; He, F.; Rolczynski, B. S.; Lou, S. J.; Chen, L. X.; Yu, L. Examining the Effect of the Dipole Moment on Charge Separation in Donor-Acceptor Polymers for Organic Photovoltaic Applications. J. Am. Chem. Soc. 2011, 133, 20468–20475.
- Liang, Y.; Xu, Z.; Xia, J.; Tsai, S.-T.; Wu, Y.; Li, G.; Ray, C.; Yu, L. For the Bright Future-Bulk Heterojunction Polymer Solar Cells with Power Conversion Efficiency of 7.4%. Adv. Mater. 2010, 22, E135–E138.
- Liang, Y,; Feng, D.; Wu, Y.; Tsai, S.-T.; G Li, G.; Ray, C.; Yu, L. High Efficient Solar Cell Polymers Developed via Fine-tuning Structural and Electronic Properties”, J. Am. Chem. Soc. 2009, 131, 7792-7799.
- Díez-Pérez, I.; Hihath, J.; Lee, Y.; Yu, L.; Oleynick, I.; Tao, N. Rectification behavior on single-molecular junctions Diode behavior on single-molecular junctions: current density limit? Nat. Chem. 2009, 1, 635-641.