|We apply modern tools in ultrafast laser spectroscopy and surface imaging to a broad range of problems in condensed phase structure and dynamics. Most of the problems relate to biopolymers. These have the beauty of touching on basic questions in the field of molecular photophysics, while aiming at insights urgently needed for design and optimization of devices in biotechnology and solar energy conversion.|
Electrochemical control of topology of immobilized biosystems. This research addresses DNA-, protein-, and hybrid DNA-protein structures which are immo-bilized at macroscopic surfaces or at nanoparticles. The focus is on the dynamics of electronically excited states in tailored architectures reporting on processes as excitation energy transfer, electron transfer, and proton transfer as well as on disorder phenomena, conforma-tional fluctuations, and self-organisation. These object-tives are pursued in a joint effort focussing on one hand on the design and synthesis of functional DNA, protein and hybrid structures and, on the other, on a variety of experimental techniques involving the measurement of excited state lifetimes and the identification of deactivation pathways in the femtosecond to the subnanosecond range. When performed under confocal conditions, fluorescence lifetime profiles yield temporal and spatial information with a resolution of single domains and possibly single molecules. A novel feature of our approach is the control of disorder-order transitions by the fluorescence lifetime profile of single domains in an electrochemical potential.
Structure-based dynamics in DNA and proteins. Our interest is in the dynamics of electronically excited states, their intramolecular and intermolecular interactions including charge transfer and conformational relaxation. In this spirit we have recently extended femtosecond time-resolved studies to more complex and most relevant DNA structures as quadruplexes and also to nucleosomes with focus on in situ photorepair of light-induced defects (thymine cyclobutane dimers). The role of conformational flexibility in charge transfer processes, one of the still open questions in the field of charge transport in DNA, is studied using DNA double strands which carry changes in the sugar-phosphate backbone.
In the area of proteins, apart from the effect of non-canonical amino acids on the excited state dynamics in GFP, the Green Fluorescent Protein, we study at present how the lifetime of a single excited tryptophan responds to the presence of ATP at the periphery of a specific subunit of the molecular motor enzyme ATPase.
Development of optimized molecular/semiconductor hybrid systems for solar cells. Conversion of solar radiation to electrical energy can be performed by excitation of a dye or other light-absorbing material (preferentially quantum dots) followed by a transfer of the electron into a semiconductor and from there into another part of the circuit, thus providing an efficient source of electricity. A principal problem of such devices is the back reaction, in which the electron returns to the electron deficient injector instead of contributing to an electric current. New activities in our group are dedicated to the development and examination of novel electron injecting systems which are expected to show a drastically reduced back reaction, thus enhancing the efficiency of the solar conversion device.
- E. E. M. Chia, C. La-o-vorakiat, T. Salim, J. Kadro, M. T. Khuc, R. Haselsberger, L. Cheng, H. Xia, G. G. Gurzadyan, H. Su, Y. M. Lam, R. A. Marcus, M. E. Michel-Beyerle. (2017). Next-Generation Spectroscopic Technologies X: Role of disorder and recombination kinetics in the performance of CH3NH3PbI3 perovskite films (Conference Presentation). Defense + Commercial Sensing 2017, Conference 10210: Next-Generation Spectroscopic Technologies X (pp. 1021011)Anaheim, California, United States: SPIE.
- c. La-o-vorakiat, L. Cheng, T. Salim, R. Marcus, M.- E. Michel-Beyerle, Y. M. Lam and E. E. M. Chia. (2017). Phonon features in terahertz photoconductivity spectra due to data analysis artifact: A case study on organometallic halide perovskites. Applied Physics Letters, 110, 123901.
- C. La-o-vorakiat, T. Salim, J. Kadro, M. T. Khuc, R. Haselsberger, L. Cheng, H. Xia, G. G. Gurzadyan, H. Su, Y. M. Lam, R. A. Marcus, M. E. Michel-Beyerle, E. E. M. Chia. (2016). Erratum: Elucidating the role of disorder and free-carrier recombination kinetics in CH3NH3PbI3 perovskite films (Nature Communications (2015) 6 (8903) DOI:10.1038/ncomms8903). Nature Communications, 7(11054), 1.
- C. La-o-vorakiat, H. Xia, J. Kadro, T. Salim, D. Zhao, T. Ahmed, Y. M. Lam, J.-X. Zhu, R. A. Marcus, M.-E. Michel-Beyerle and E. E. M. Chia. (2015). Phonon Mode Transformation Across the Orthohombic–Tetragonal Phase Transition in a Lead Iodide Perovskite CH3NH3PbI3: A Terahertz Time-Domain Spectroscopy Approach. Journal of Physical Chemistry Letters, 7(1), 1-6.
- C. La-o-vorakiat, T. Salim, J. Kadro, M. T. Khuc, R. Haselsberger, L. Cheng, H. Xia, G. G. Gurzadyan, H. Su, Y. M. Lam, R. A. Marcus, M. E. Michel-Beyerle, E. E. M. Chia. (2015). Elucidating the role of disorder and free carrier recombination kinetics in CH3NH3PbI3 perovskite films. Nature Communications, 6(7903), 1 - 7.