Spectroscopic and Theoretical Characterization of Retinylidene Proteins and Biological Chromophores for Use in Biophotonic Applications

Retinylidene proteins are found in all domains of life and perform diverse biological functions, including light-induced ion transport and phototransduction in visual systems. One such protein, bacteriorhodopsin (BR), is the light-activated proton pump that produces chemical energy for the archaeon, Halobacterium salinarum. In recent years, a branching reaction from the photocycle of BR has been discovered to produce a stable photoproduct, the Q state, using a sequential multiphoton process. The Q state has optical properties that enable the use of BR in bioelectronic technologies, however, the native protein has limited access to this photoproduct. A review is presented on the associative processors and optical memories that are based on BR mutants with enhanced photochemical properties. The BR mutant, V49A, is identified as an efficient Q-forming mutant, and the pH-dependent mechanism that governs the photochemistry of V49A is investigated. This mutant is also characterized in the context of a protein-based retinal implant. Moreover, this thesis includes two reports involving the spectroscopic and theoretical analysis of various porphyrinoids for application in optically driven biotechnologies. The first is an analysis of the two-photon absorptivities of tertraphenyl-porphyrins and -chlorins, which reveal that the nonlinear optical properties are sensitive to macrocycle distortion. Secondly, absorption spectroscopy and excited state calculations describe the relationship between the structural features of trithienyl-corrole and the resulting optical properties. Lastly, low-temperature trapping of the rhodopsin E181Q mutant is investigated to elucidate the role of residue Glu-181 during the early photostationary states of the photobleaching sequence