Graduation Year

2025

Document Type

Thesis

Degree

M.S.

Degree Name

Master of Science (M.S.)

Degree Granting Department

Chemistry

Major Professor

Randy Larsen, Ph.D.

Committee Member

Chavdar Slavov, Ph.D.

Committee Member

John Kuhn, Ph.D.

Keywords

Metal-Organic Frameworks, Photocatalysis, Photophysics, Porous Materials, Porphyrins, Spectroscopy

Abstract

Porphyrins are versatile aromatic macrocycles with unique photophysical properties that make them attractive for applications in light harvesting, photocatalysis, and sustainable energy conversion. Incorporating porphyrins into metal-organic frameworks (MOFs) offers a unique opportunity to modulate their photophysical behavior through spatial confinement and host–guest interactions. This thesis explores how structural modifications influence porphyrin excited-state behavior through a multi-stage investigation. The work begins by comparing the photophysical properties of two cationic porphyrins: tetra(N-methylpyridyl) porphyrin(TMPyP) and tetra(4-N,N,N-trimethylanilinium) porphyrin(4TANP). While TMPyP exhibits significant singlet–charge transfer (S₁–CT) state mixing due to charge delocalization onto peripheral pyridinium groups, 4TANP lacks comparable behavior. The localized nature of its anilinium substituents prevents effective CT state formation, as confirmed through steady-state spectroscopy and emission lifetime analysis. Building on these findings, 4TANP was encapsulated into a crystalline metal-organic framework (MOF), MOM-11, to probe the effect of spatial confinement on its photophysics. Structural analysis revealed distorted porphyrin conformations within the MOF cavities, and changes in emission profiles indicated perturbations in excited-state dynamics due to host–guest interactions. To further explore energy and electron transfer in confined systems, a mixed-bed MOF architecture was developed by co-encapsulating a ruthenium complex (RuBpy) as an energy donor and cobalt(III) tetra(4-sulfonatophenyl)porphyrin (Co4SP) as an electron-deficient acceptor within HKUST-1(Zn). Spectroscopic studies demonstrated spectral overlap conducive to Forster resonance energy transfer (FRET), and lifetime measurements showed dynamic quenching of RuBpy upon increasing Co4SP loading. Stern–Volmer analysis supported a reductive photoinduced electron transfer (PET) pathway with cavity-dependent efficiency, while FRET remained active over longer donor–acceptor distances. These findings collectively illustrate the importance of electronic structure, substituent design, and spatial confinement in modulating porphyrin photophysics. This work provides insights into the design of MOF–porphyrin hybrid materials for targeted applications in photocatalysis, molecular electronics, and artificial photosynthesis.

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