Date of Award

8-2025

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

School

Mathematics and Natural Sciences

Committee Chair

Dr. Karl J Wallace

Committee Chair School

Mathematics and Natural Sciences

Committee Member 2

Dr. Julie Pigza

Committee Member 2 School

Mathematics and Natural Sciences

Committee Member 3

Dr. Song Guo

Committee Member 3 School

Mathematics and Natural Sciences

Committee Member 4

Dr. Wujian Miao

Committee Member 4 School

Mathematics and Natural Sciences

Committee Member 5

Dr. Sarah Morgan

Committee Member 5 School

Polymer Science and Engineering

Abstract

Fluorescent chemosensors based on the coumarin scaffold are versatile tools for detecting analytes with high sensitivity and selectivity. The tunable photophysical properties of coumarin derivatives make them ideal for environmental monitoring, biological imaging, and chemical threat detection applications. Thus, this work presents using coumarin-based fluorescent chemosensors to detect metal cations and organophosphate compounds through distinct sensing mechanisms, such as CHEF, CHEQ, and PET.

A coumarin-enamine molecular probe has been extensively studied in organic solvents for the detection of metal ions. However, the probe undergoes rapid hydrolytic cleavage in aqueous media, limiting its application for environmental and biological sensing. To address this limitation, the probe was encapsulated using water-soluble macrocycles such as beta-cyclodextrin and cucurbit[7]uril. The inclusion complex was studied in binary solvent systems, including 90:10, 75:25, 50:50, 25:75, and 1:99 DMSO:HEPES buffer (25 mM, pH 7.4), and exhibited distinct spectroscopic responses towards divalent metal cations (Cd2+, Co2+, Cu2+, Ni2+, and Zn2+). Macrocyclic encapsulation of the probe is an effective strategy to enhance aqueous compatibility while preserving the probe’s ability to bind metal ions.

Two quinoline-functionalized coumarin-hydrazone probes were studied for their ability to bind divalent metal cations in organic-aqueous media. These chemodosimeters exhibit significant fluorescence enhancement upon binding closed-shell metal ions. The photophysical behavior, coordination geometry, and binding affinity of the probes in the presence of these metal ions have been extensively studied in DMSO and HEPES buffer (25 mM, pH 7.4) solvent mixtures. Confocal microscopy confirmed the ability of the probes to detect free Cd2+ and Zn2+ ions in live HEK293 cells and distinguish between their cellular distribution, demonstrating the potential of these probes for cellular imaging applications.

A coumarin oxime probe was developed for the detection of organophosphate nerve agent simulants. Photophysical characterization of the probe was carried out in polar organic solvents and revealed an increase in Stokes shift and fluorescence intensity with increasing solvent polarity factor. Upon the addition of Verkade’s superbase, the oxime was converted to the oximate, initiating a photoinduced electron transfer mechanism that quenched the fluorescence intensity. The oximate selectively reacted with nerve agent simulants with the strongest responses observed for DFP and DICP, which restored 80% of the emission intensity.

ORCID ID

0009-0001-4357-6232

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