Speech

1. Speech Subject : Interaction of aromatic molecules with carbon nanotubes : spectroscopy and photophysics. Speaker : Prof. Jacques Delaire , Ecole Normale Superieure (ENS) de Cachan, France; Director of Laboratory of Photophysics and Photochemistry of Supramolecules and Macromolecules (PPSM, CNRS) Time : 10:00-11:00 AM, March 8, 2007 (Thursday) Place : Conference Room 307B, NDL Abstract : In the recent years there has been considerable interest in the functionalization of single wall carbon nanotubes (SWNT) aimed at the control of their properties. In particular, light excitation could modify the semiconducting or metallic properties of the SWNT. By irradiation, charge separation and electron photoinjection could change in a simple and controllable way the electronic properties of the SWNT. At PPSM, we investigated different systems in which SWNT are either non covalently covered with aromatic molecules interacting by p-stacking, or systems in which the aromatic molecule is covalently linked to the SWNT. Two anionic water soluble porphyrins have been shown to adsorb on single-walled carbon nanotubes (SWNT) and dissolve them in water. The adsorption of these porphyrins leads to a unique spectral change in the shape and position of their Soret band. Steady-state and time resolved studies show that the adsorbed porphyrins are non fluorescent, i.e. the excited state is quenched in the adsorbed state. SEM images revealed that most of the dissolved nanotubes are bundled in thesolution. On the contrary, the two cationic porphyrins studied do not lead to solubilization of SWNT in water, even if they adsorb on their surface. This drastic difference associated with the ionic charge of the porphyrins is explained by a difference in the charge delocalisation of the p electronic cloud on the surface of the macrocycle at the origin of the formation of the adsorbate. SWNT functionalized with covalently linked aromatic structures were also studied. First, phenyl acridine linked to SWNT leads solubilisation of these SWNT in different solvents. We put into evidence exciplex formation after photoexcitation of the acridine moiety. After methylation, the methylacridinium derivative gives rise to photo-electron transfer to SWNT after photoexcitation. Second, fullerene linked to SWNT shows enhanced optical limiting compared with pure SWNT suspensions. Expected applications of these systems will be discussed. Biographical notes : Prof. Jacques Delaire received his Ph.D. in Chemistry from Paris XI University (Orsay) in 1980 in the field of radiation chemistry. He has been at the head of the Laboratory of Photophysics and Photochemistry of Supramolecules and Macromolecules (PPSM, ENS Cachan and CNRS) since 1998. His main domains of interest are photophysics and nonlinear optics of molecular materials, with a special emphasis on the coupling between different properties like photochromism and nonlinear optics. He is a member of the Editorial Board of Journal of Photochemistry and Photobiology (Part A). He has been invited to give lectures in different international conferences and is the author of more than one hundred papers. 主辨單位:國立台灣大學應用力學研究所、國立清華大學微機電所、國家奈米元件實驗室