Phys/ANE/ChemPhys Joint Seminar

Date
Wed, Dec 7, 2022 11:00 am - 12:00 pm
Location
IPST Building #085, 1116 Conference Room

Description

Speaker: Dr. Bern Kohler, Ohio State University

Title: 
The Melanin Elephant: A Spectroscopist’s View of Nature’s Mysterious Pigment

Abstract: Melanins are ubiquitous natural pigments that color human skin, overripe bananas, cephalopod ink, and iridescent peacock feathers to name just a few examples. While sunscreening is the best-known function of melanin in skin, melanins also bind metal ions and scavenge radicals. Property emergence in melanins is of great interest not only for understanding their biological function but also for creating bioinspired, multi-functional materials that exploit melanin’s intrinsic electronic and ionic conductivity, redox activity, ability to stabilize free radicals, and broadband optical absorption. These properties are attractive for applications in bioelectronics, catalysis, energy conversion and storage. Remarkably, the atomistic structures present in melanins are obscure despite more than a century of effort, impeding understanding of their structure-function relationships. To gain insight into the chromophores of melanin, femtosecond transient absorption experiments have been carried out on synthetic melanin polymers. Transient spectral holes centered about the laser excitation wavelength are detected at room temperature, providing evidence of absorbers with a broad distribution of transition energies. The observed bleach recovery dynamics provide valuable insights into couplings among melanin’s chromophores. By combining femtosecond time-resolved infrared (TRIR) spectroscopy with the ability to select chromophore subensembles with a tunable UV-vis excitation pulse, a vibrational fingerprinting technique is demonstrated that correlates electronic and vibrational properties of melanin’s chromophores. These top-down studies are augmented by a bottom-up research program to construct a melanin mimic from structurally well-defined subunits. This work has led to intriguing stabilized quinones that reproduce several of melanin’s hallmark properties.