Mechanisms of Porphyrinoid and Carotenoid Spectral Tuning Revealed with Quantum Chemistry

Continued advances in a myriad of biomedical and technological fields require the rational design of molecules or supramolecular architectures with specific photophysical properties. Central to this endeavor is a mechanistic understanding of optical property modulation as a function of molecular structure, conformation, and environment. Natural pigments and protein-pigment complexes constitute a ‘solutions manual’ to challenges in electronic (optical) engineering that has been refined over a few billion years of evolution, and from which design principles can be deduced. In this thesis, unique mechanisms for modulating the optical properties of natural or synthetic porphyrinoid and carotenoid pigments are elucidated with quantum chemical methods. Our investigations add a new conformational mechanism, as well as design principles for regioisomer-dependent electronic substituent effects to the cannon of structural tools for regulating the optical properties of pyrrole-modified porphyrins. The lessons learned provide insight into analogous spectral tuning mechanisms found in nature. We also delineate the molecular factors optimally regulating light harvesting in a natural photosynthetic antenna complex. These discoveries have advanced the fundamental understanding and practical utilization of structure-optical property modulation mechanisms, and may aid the design of next-generation photonic-based technologies