Collaborative Research: Electronic Coherence Effects in Multichromophore Systems Probed by Two-Dimensional Electronic Spectroscopy

North Carolina State University, Raleigh NC

Investigators

Abstract

In this collaborative project, co-funded by the Chemical Structure, Dynamics & Mechanisms B and the Chemical Structure, Dynamics & Mechanisms A programs of the Chemistry Division, Professor Lin X. Chen of the Department of Chemistry at Northwestern University and Professor Felix N. Castellano from the Department of Chemistry at North Carolina State University lead a project to understand the effects of coherent electronic motions in energy and electron transfer in distinct classes of multi-chromophoric synthetic platforms. The knowledge obtained through the proposed studies will greatly enhance the ability to rationally design chemical materials/devices for catalysis, optoelectronics, and energy sustainability. The proposed research engages University graduate students to use advanced laser spectroscopy for characterization, incorporates state-of-the-art computational chemistry for quantum mechanical and molecular dynamics modeling, and utilizes advanced chemistry laboratory facilities for molecular syntheses and structural characterization, engendering them with expansive training necessary for the development of multidisciplinary scientific expertise. The proposed research/education activities are integrated with numerous K-12 public outreach activities at both universities, including Photonics Day at North Carolina State University and NU Bond at Northwestern University. Specifically, they will employ newly developed two-dimensional electronic spectroscopy in their studies with very high time resolution of approximately 6 femtoseconds. The rationally designed molecules are engineered to tune electronic coupling in their excited states, which are either responsible for or can be correlated to electronic coherence originating from in-phase motions of electrons induced by photoexcitation. The measured coherences will be correlated with the observation of photoinduced intramolecular energy and/or electron transfer chemistry and rationalized using continuously developing theory to assess the role of electronic and/or vibronic coherence in these fundamental primary processes related to light activation. Two types of molecular designs are targeted for these investigations: (1) Pt(II) dimers bridged by hydroxypyridines featuring metal-metal-to-ligand charge transfer excited states where a metal-metal bond is transiently formed following light excitation; and (2) Pt(II) dimers whose terminal cyclometalating ligands are decorated with bay-substituted naphthalenediimide based energy and/or electron acceptors. The proposed project seeks to glean new insight into excited state chemistry and how this knowledge can be leveraged to control reactivity in condensed phases, molecular photonics, and photocatalysis. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.