Naphthalenediimide-Based Hybrid Material with Eu-Substituted Polyoxometalate: Photochromism, Near-Infrared Photothermal Conversion, and C-3 Functionalization of Indoles

Designing and developing novel photochromic materials with additional functions such as photothermal conversion and photocatalysis are challenging but meaningful objectives. Crystalline naphthalenediimide (NDI)-based hybrids are an attractive class of multifunctional materials with fast-response photoinduced electron transfer and charge separation properties. They are promising photothermal conversion materials and photocatalysts. Herein, a novel hybrid material, EuPMo₁₁O₃₉(L)_1.5(H₂O)₂]·DMA (EuMo-NDI) (L = N,N′-di(1-oxido-4-pyridyl)-1,4,5,8-naphthalenediimide), was prepared with a solvothermal method, integrating a photoactive NDI derivative and an Eu-substituted polyoxometalate. EuMo-NDI exhibits 0D structure with sensitive photochromic behavior under UV–vis light irradiation due to fast-response photoinduced electron transfer between its components. The colored EuMo-NDI sample demonstrated efficient near-infrared photothermal conversion due to the strong absorption of the photogenerated radical anion NDI^•– and mixed valence heteropoly blue in the near-infrared region. Meanwhile, EuMo-NDI is easily excited in the presence of electron donors to form the radical species, which can activate inert O₂ to superoxide radical O₂^•–. EuMo-NDI exhibited high photocatalytic activity for C-3 thiocyanation of indoles under mild conditions using white light as a driving force. This work provides an effective avenue to design novel photothermal conversion materials and photocatalysts using photochromic materials as platforms.