Collaborative Research: Investigating Structural Dynamic Coherences of Transition Metal Complexes in Photochemical Processes

In this project funded by Chemical Structure, Dynamics and Mechanisms B program of Chemistry Division, Professors Lin Chen of Northwestern University and Felix Castellano of North Carolina State University are developing spectroscopic and synthetic methods to investigate how multiple metal centers in transition metal complexes (TMCs) act cooperatively to convert and accumulate energy from sunlight to multiple electronic potentials that ultimately will drive catalytic reactions for generating fuels. The proposed research is in line with the NSF Strategic and Performance Goals to transform the frontiers and innovate for society. The knowledge obtained through the proposed studies could be transformative for the chemical sciences and will greatly enhance our ability to rationally design chemical materials/devices for catalysis, optoelectronics and energy sustainability. The research activity engages university graduate students to use the advanced laser facility for characterization and advanced chemistry lab facilities for materials synthesis, providing them with a unique training ground for the development of multidisciplinary expertise. Such training is urgently needed for the next generation STEM workforce in order to explore the frontier of chemical science and to keep the US globally competitive at the frontiers of knowledge. The proposed research/education activities are integrated with public outreach and mentoring aimed at young scientists, including undergraduate students inside and outside of the University (especially female, minority, and underrepresented local college students) through collaborative training, summer school and education focused symposiums.

This work aims at controlling materials processes at the level of electrons by engineering structural factors to influence intramolecular electronic interactions and system-bath interactions on the time scale of coherent electronic and atomic motions. The mechanistic details enabling multiple-electron conversion will be investigated by newly developed two-dimensional electronic spectroscopy (2DES) and optical anisotropy spectroscopy applied to new molecular architectures. The proposed work aims at understanding intrinsic electronic couplings between the multiple metal centers TMCs and their influence on photochemical reactions. The work will engineer intrinsic coherent motions in a series of di-platinum complexes via systematically varying structural factors, such as the inter-platinum distances as well as the steric hindrance/energetics/size/conjugation of the ligands, resulting in systematic changes of the energy levels of the molecular orbitals. The researchers will use external perturbations, i.e. laser pulses, to shift electron density on a time scale faster than the period of the ground state Pt-Pt stretch, and follow with systematic investigations of dipole correlations by transient optical anisotropy, electronic couplings by two-dimensional electronic spectroscopy. They will further investigate the implications of these coherent motions in chemical and photochemical processes.