Flavins play a crucial role in biological redox processes and photoreception, inspiring the development of synthetic analogs for applications in organic, bio-, and photochemistry. However, fine-tuning their electronic and optical properties remains a challenge. In this study, we report a series of novel pentacyclic flavins (C-PF, O-PF, and S-PF) featuring tailored electronic structures and distinctive photophysical behaviors. The introduction of different heteroatoms (O, S, and C(Me)₂) at the C(9) position of the isoalloxazine core induces geometric confinement within the fused five-ring system, leading to significant changes in their optical characteristics. Furthermore, additional investigations utilizing S-PF led to the successful synthesis of O=S-PF, expanding the structural diversity of these systems. Notably, the unique electronic properties of O=S-PF suggest their potential application in light-driven C–H functionalization. Comprehensive spectroscopic and structural analyses, including single-crystal X-ray diffraction, NMR, UV/vis/NIR absorption and emission spectroscopy, and cyclic voltammetry, are complemented by density functional theory (DFT) and time-dependent DFT (TDDFT) calculations, providing deeper insight into the structure-property relationships of these unique flavin derivatives.