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Richard Barry Bernstein Collegiate Professor of ChemistryProfessor of Chemistry, LSAProfessor of Macromolecular Science and Engineering, College of Engineering
Office Location(s): 4819 Chemistry
Our research group utilizes a number of spectroscopic techniques towards investigating the optical properties and applications of novel organic macromolecular materials. A major emphasis is placed on the new properties observed in organic macromolecules with branching repeat structures as well as organic macromolecules encapsulated with small metal particles. These materials have been suggested to be candidates for variety of applications involving light emitting devices, artificial light harvesting, strong optical limiters, enhanced nonlinear optical effects, quantum optical effects and as sensors in certain organic and biological devices.
Utilizing steady-state spectroscopy as well as ultra-fast time-resolved fluorescence (Upconversion) and absorption (pump-probe) measurements our research is focused on probing the kinetics of the fast energy redistribution processes that occur in branched (and related) macromolecular structures. With the additional use of fluorescence anisotropy decay measurements, we have characterized the fundamental limits of interaction in different molecular architectures. Investigations of novel larger branched structures (obtained through collaboration) as well as more fundamental investigations (were the synthesis of model compounds is carried in our lab) are used to probe the important structure-function relationships in these systems. These investigators are coupled with measurements of interactions and electronic dephasing in the branched (aggregate) systems with 3-pulse photon echo spectroscopy (3PEPS). This combined approach allows for the analysis of the energy transfer, interaction strength, dephasing, as well as other important physical properties of particular macromolecular systems.
The research in the group is also directed at the use of organic branched structures for applications in nonlinear optics as well as quantum optical and quantum interference effects. The investigations of strong interactions in particular multi-chromophore systems suggest that there is a possibility of enhanced transition dipole moments. This has been observed in organic branched structures in our laboratory. New methods, both synthetically and optically to enhance the nonlinear response of organic branched macromolecules are developed in this research effort. These measurements are combined with two-photon-emission and degenerate-four-wave mixing experiments to fully characterize the complete response of novel materials.
The initial investigations utilizing organic materials in quantum optical phenomena were carried out in our laboratory. This included measurements of photon number squeezed states of light in an organic polymeric material. The ability to reduce the photon fluctuation below the shot-wave limit is of significant use to those interested in an all optical telecommunication system. The striking result was that the organic material gave rise to the same magnitude of " squeezed light" as was observed for inorganic systems with interactions lengths that was orders of magnitude longer. Our recent investigations in this area include measurements of entangled photon and their use in the spectroscopy of organic materials at low photon-number as well as other novel quantum interference effects with organic materials.
Department of Chemistry
930 N. University
Ann Arbor, MI