Polydopamine (PDA) is an advanced functional material and its emergent light absorption properties make it crucial for applications in materials science. However, it is challenging to rationally design and regulate PDA absorption properties due to its complex architecture. In a new report, Yuan Zou and a team of researchers in polymer science, optoelectronic materials and physical chemistry in China proposed a simple method to regulate the light absorption behaviors of PDA. To accomplish this, they constructed donor-acceptor pairs in the microstructures via connections between specific chemical moieties. They then used detailed structural and spectral analysis as well as density functional theory (DFT) simulations to confirm the existence of such donor-acceptor molecular pairs. The molecular pairs could decrease the energy bandgap (or energy gap where no electrons exist) and increase electron delocalization to enhance light absorption across a broad spectrum. The rational design of PDA nanoparticles with tunable absorption properties allowed an improved photothermal effect, which the team demonstrated with excellent performances during solar desalination. The work is now published on Science Advances.