Special Seminar
Name: Prof. David M. Jonas
Affiliation: Department of Chemistry, University of Colorado Boulder
Title: Generalized Einstein Relations between Absorption and Emission Spectra: a Theory of Fluorescence, Excited State Thermodynamics, and Extreme Stokes’ Shifts
Date & Time: Friday, 22nd November at 11:00 a.m.
Venue: Rajarshi Bhattacharya Memorial Lecture Hall, Chemical Sciences Building
Abstract:
We have derived single-molecule relationships between absorption and thermal equilibrium emission spectra by using detailed balance with Planck blackbody radiation and the quantum electrodynamic connection between stimulated and spontaneous emission.[1] These thermodynamic relationships between spectra resolve the conflict between infinitely narrow lines, a finite spontaneous emission rate, and the time-energy uncertainty principle. They contain Einstein’s relationships for line spectra as a limiting case and predict the Stokes’ shift between broadened absorption and emission spectra.For Boltzmann statistics, they allow direct measurement of the standard free energy change upon electronic excitation. These single-molecule relationships do not apply directly to inhomogeneously broadened 1D spectra, but their validity can be probed with 2D spectroscopy, as we have demonstrated for colloidal PbS quantum dots[2] For molecules that satisfy three criteria, they supply a theory of ensemble fluorescence that connects it to absorption without adjustable parameters, thus allowing us to substantially improvethe NIST and BAM calibration procedures for fluorescence spectrometers.[3] For other molecules, recording theirensemble lineshapes and ensemble Stokes’ shift under suitable conditions can provide information on molecular heterogeneity and the single-molecule lineshape. We have tested the spectroscopic standard free energies for a photobase by replacing Förster’s approximate cycle for excited state proton transfer equilibria with a true thermodynamic cycle. Finally, the relations predict Stokes’ shifts so extreme that the forward and reverse transitions are both absorptive; molecular examples of this phenomenon will be discussed.
References:
1. Proceedings of the National Academy of Sciences of the USA 2024, 121, e2410280121.
2. Science Advances 2021, 7, eabf4741.
3. Pure and Applied Chemistry 2012, 84, 1815.
About the speaker:
David M. Jonas is a Professor of Chemistry at the University of Colorado, Boulder. He completed his Ph.D. from MIT in 1992, jointly under Prof. Robert F. Field and Prof. Robert J. Silbey. He was an NSF Fellow at the University of Chicago from 1992-1994 in the group of Prof. Graham Fleming. In 1998, as an Assistant Professor at the University of Colorado, David Jonas demonstrated the first femtosecond analogs of two-dimensional Fourier transform NMR, thus founding the modern field of femtosecond multidimensional Fourier transform spectroscopy. Femtosecond 2D FT spectra are now used from terahertz to ultraviolet frequencies for studies of dynamics in all phases of matter.
Femtosecond multidimensional spectroscopy has revolutionized our understanding of ultrafast phenomena at the interface of physics, chemistry, and biology, such as natural photosynthesis, photocatalysis, photovoltaics, and layered quantum materials. David’s contributions have impacted not only the development of multidimensional spectroscopy methods but have also broadly impacted the conceptual frameworks behind ultrafast electronic and vibrational dynamics.
David Jonas is a Fellow of the American Association for the Advancement of Science (AAAS), the Optical Society of America (OSA) and the American Physical Society (APS). For his seminal contributions to the field of multidimensional spectroscopy and molecular spectroscopy in general, David was awarded the E. Bright Wilson Award in Spectroscopy (2023), the Earle K. Plyler Prize for Molecular Spectroscopy and Dynamics (2018) and the Ahmed Zewail Award in Ultrafast Science and Technology (2013).