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.

Polydopamine (PDA) is a major type of artificial melanin material with many interesting properties such as antioxidant activity, free‐radical scavenging, high photothermal conversion efficiency, and strong metal‐ion chelation. The high affinity of PDA to a wide range of metals/metal ions has offered a new class of functional metal‐containing polydopamine (MPDA) nanomaterials with promising functions and extensive applications. Understanding and controlling the metal coordination environment is vital to achieve desirable functions for which such materials can be exploited. MPDA nanomaterials with metal/metal ions as the active functions are reviewed, including their synthesis and metal coordination environment and their applications in catalysis, batteries, solar cells, capacitors, medical imaging, cancer therapy, antifouling, and antibacterial coating. The current trends, limitations, and future directions of this area are also explored.

Raman spectroscopy has been an integral part of graphene research and can provide information about graphene structure, electronic characteristics, and electron-phonon interactions. In this study, the characteristics of the graphene Raman D-band, which vary with carrier density, are studied in detail, including the frequency, full width half-maximum, and intensity. We find the Raman D-band frequency increases for hole doping and decreases for electron doping. The Raman D-band intensity increases when the Fermi level approaches half of the excitation energy and is higher in the case of electron doping than that of hole doping. These variations can be explained by electron-phonon interaction theory and quantum interference between different Raman pathways in graphene. The intensity ratio of Raman D- and G-band, which is important for defects characterization in graphene, shows a strong dependence on carrier density.

Commercial sunscreens usually rely on multiple component formulas against solar irradiation, including UV filters, antioxidants, and nanomaterial matrices. While many efforts are devoted, concern has arisen that the effectiveness and safety issues of most sunscreens are largely limited by their complex formulations, photostability, and toxicity. Inspired by skin pigmentation as primary photoprotective mechanism in human body, novel sunscreen products based on polydopamine (PDA) gels, with a bioinspired protection concept and improved photoprotective capacities, were rationally designed and facilely prepared. The diverse formula of those sunscreen gels can be achieved by the use of PDA nanoparticle, a kind of naturally melanin mimics, to complex/conjugate with different polymers. The resulting PDA sunscreens are bioadhesive, water resistant, and nonskin penetration, yet can be directly removed by towel wiping. They also perform many promising features including superior UV shielding properties, high in vitro and in vivo UV protection efficiencies, nonphototoxicity, and nonirritating nature. These PDA materials in an initial proof‐of‐concept study were described and it is proposed that this class of bioinspired gels will be useful for incident UV protection where simple, safe, and efficient sunscreens are still highly desirable.