Carbon dots modified with polydopamine (CDs/PDA), a low‐cost and environmentally friendly photothermal material, is prepared in this work. The results show that the polymerization of dopamine is significantly accelerated due to the interaction between CDs and dopamine. Importantly, the interaction also greatly promotes nonradiative recombination of photoexcited charge carriers, thereby enhancing the photothermal conversion performance of CDs/PDA. The obtained CDs/PDA composite shows superior photothermal evaporation efficiency in comparison with CDs and PDA owing to the enhanced light absorption, porous structure, and appropriate interaction. In addition, CDs/PDA exhibits excellent stability. These merits enable CDs/PDA show great promise in solar‐energy‐related applications.

A light-responsive optical switching material is reported, which was obtained by incorporating carbon dots (CDs) into thermochromic hydroxypropylmethyl cellulose (HPMC). The ultrasmall size of CDs guarantees the considerable transparency of CDs/HPMC. Under illumination, CDs/HPMC shows rapid and reversible optical switching between transparent and opaque states due to the remarkable photothermal effect of CDs. Moreover, the interaction between CDs and HPMC enhances the light absorption and boosts the nonradiative recombination of photoexcited charge carriers that further promote the photothermal conversion of CDs, and also ensures the structural stability of the composite. The obtained CDs/HPMC with good reversibility and high sensitivity which can dynamically switch their transparency in response to weather conditions exhibits excellent solar modulation ability.

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