Polydopamine (PDA) has been increasingly exploited as an advanced functional material, and its emergent light absorption property plays a crucial role in determining various utilizations. However, the rational design and efficient regulation of PDA absorption property remain a challenge due to the complex structure within PDA. In this work, we propose a facile method to regulate the light absorption behaviors of PDA by constructing donor-acceptor pairs within the microstructures through the chemical connections between indoledihydroxy/indolequinone and their oligomers with 2,2,6,6-tetramethylpiperidine-1-oxyl moiety. The detailed structural and spectral analysis, as well as the density functional theory simulation, further confirms the existence of donor-acceptor molecular pair structures, which could decrease the energy bandgap and increase the electron delocalization for enhancing light absorption across a broad spectrum. These rationally designed PDA nanoparticles with tunable absorption properties also show improved total photothermal effect and demonstrate excellent performances in solar desalination.