Cryptochromes, a class of proteins, exhibit a remarkable complexity beyond mere amino acid sequences. These proteins often house smaller molecules within their peptide chains, with one intriguing tenant being the flavin adenine dinucleotide (FAD) molecule. FAD boasts unique photochemical properties, particularly its light-absorption abilities in the blue region of the visible spectrum. More intriguingly, FAD's excited state can trigger the formation of a radical pair inside cryptochrome.
Our scientific endeavor is centered on employing cluster models of cryptochromes, where we narrow our focus to the quantum mechanically relevant regions. We turn to the formidable tool of time-dependent density functional theory to explore and understand the photoabsorption capabilities of FAD within cryptochrome. We aim to bridge the gap between theory and the natural world, unraveling the mysteries of this intricate relationship and shedding light on the underlying principles that govern these bio-molecular interactions.