1.
일시 : 2015년 11월 16일(월) 오전 11:00
장소 : 아산이학관 433호
연사 : Professor T. David Harris(Department of Chemistry, Northwestern University)
제목 : Semiquinoid Radical-Containing Molecules and Solids with Strong Magnetic Exchange Coupling
Abstract:
This presentation will describe our efforts to synthesize molecule-based magnets with strong magnetic exchange coupling by employing benzoquinonoid radical bridging ligands. In particular, a series of tetraazalene radical-bridged dinuclear complexes has been synthesized. Magnetic measurements of these complexes reveals the presence of strong antiferromagnetic exchange between MII centers and radical, with estimated coupling constants of J = −157 (Mn), −307 (Fe), −396 (Co), and J = −626 (Ni) cm−1. The Fe congener behaves as a single-molecule magnet with a spin relaxation barrier of Ueff = 52(1) cm−1. In addition, the synthesis and magnetic properties of a wheel-like cluster comprised of six MnII ions linked by six radical ligands will be discussed. Finally, this presentation will present a new benzoquinonoid-bridged MnII chain compound, which can undergo solid-state ligand-based redox-switching, and a 2D semiquinoid radical-containing microporous magnet with solvent-induced switching from Tc = 26 to 80 K.
2.
일시 : 2015년 11월 16일(월) 오전 11:45
장소 : 아산이학관 433호
연사 : Professor Elad Harel(Department of Chemistry, Northwestern University)
제목 : "Mapping the Vibronic Structure of Complex Systems by Single Shot Multi-Dimensional Spectroscopy"
Abstract:
Optical analogs of multi-dimensional NMR techniques allow for the study of the ultrafast dynamics of complex condensed-phase chemical and biological systems. Here, we describe advances in multi-dimensional optical spectroscopy using light sources that span the visible and near-infrared regions of the electromagnetic spectrum and allow access to the entire vibronic manifold of states. Specifically, we demonstrate acquisition of high quality spectra of cyanine dyes and the photosynthetic protein, LH2, in 1 ms with sub-6 fs temporal resolution. Unlike the majority of 2D techniques that rely on spectral interferometry to measure the signal phase, we show here that spatial, or more generally, spatial-spectral interferometry (SSI) allows for inherently higher spectral resolution along the rephasing frequency axis, while simultaneously providing significantly higher sensitivity. We discuss how this technological advance may enable two-dimensional optical spectroscopy to transform from a highly specialized technique to a general analytical tool for examining the electronic and vibrational structure of a wide range of molecular systems in real-time. In particular, we show results on the coherent dynamics of a cyanine dye in which the solvent takes the places of strongly coupled intramolecular vibrations during the first 200 fs. This measurement was enabled by the simultaneously high temporal and spectral resolution and large bandwidth from WHITE GRAPES by SSI. Finally, we discuss technical advances to enable 2D spectroscopy in the far-infrared and THz regimes, where sensitive detection is challenging. The methods described here are ideal for studying exciton transport in highly coupled molecular system at the extremes of time and energy.