Graphical Spectral Deconvolution and Ultrafast Spectroscopy of Electrostatically Bound Chromophore-Polyoxometalate Complexes

Date of Award

8-2025

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Ramakrishna Guda, Ph.D.

Second Advisor

Gellert Mezei, Ph.D.

Third Advisor

Andre Venter, Ph.D.

Fourth Advisor

Qingliu Wu, Ph.D.

Abstract

Ultrafast pump-probe spectroscopy provides the temporal resolution needed to observe primary photo-induced events that define molecular function, yet its impact is often limited by severe spectral congestion. This dissertation introduces a graphical spectral deconvolution method that removes the dominant obstacle: overlapping transient absorption signals. Our approach extends the utility of UV-Vis spectroscopy by enabling accurate quantification of target analytes in complex matrices, allowing analyses that traditionally require chromatographic separation. The graphical spectral deconvolution method cleanly isolates the spectrum of interest without assumptions about the number, shape, or kinetics of co-evolving species. Compared with singular value decomposition and global kinetic modeling, the graphical approach requires only one reference spectrum and no a-priori kinetic model, delivering a transparent, visually guided route to spectral demixing. Furthermore, this method makes transient absorption spectroscopy more accessible by providing clear absorption spectra of excited states, making TA data easier for a broader range of chemists to interpret.

Applying the deconvolution method to ground-state bleach (GSB) and stimulated emission (SE) signals allows conversion of differential absorbance into excited-state absorption (ESA) spectra, and extracting excited-state populations, ground-state recovery kinetics, and excited-state absorption coefficients, the method delivers additional essential insights into photoinduced dynamics, critical for understanding and controlling light-matter interactions. By applying the graphical deconvolution method, we isolate pure ESA spectra and determine the absolute εES, previously inaccessible in TA analysis, for a series of porphyrin derivatives (TPP, ZnTPP, TMPyP, ZnTMPyP, FeTMPyP, PdTMPyP, and TTMAPP). We further showcase the method’s analytical strength with a supramolecular chromophore-polyoxometalate (ChromoPOM) assembly designed for visible-light harvesting. The tetracationic porphyrin dye, tetrakis(N-methylpyridyl)porphine (TMPyP), was paired with Keggin-type POM anions (H3PW12O40, H4SiW12O40, Na6H2W12O40) through electrostatic self-assembly. Transient absorption data reveal pronounced acceleration of excited-state decay when TMPyP is bound to POMs, consistent with ultrafast charge transfer from the excited porphyrin to the cluster. The findings illuminate how subtle shifts in POM redox potential, charge, and binding geometry govern the balance between charge and energy transfer, establishing a structure-function map that links electronic coupling strength to substituent chemistry and POM composition.

Access Setting

Dissertation-Abstract Only

Restricted to Campus until

8-1-2027

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