Photothermal conversion property studies of polyoxophosphitemolybdate derivatives through microwave-assisted synthesis

Photothermal conversion is one of the key technologies in solar energy collection, seawater desalination, photothermal treatment and other important fields. In order to develop next generation photothermal materials, four polyoxometalates, [(CH 3 ) 2 NH 2 ] 12 H 5 [Ni 3 Mo 18 O 54 (HPO 3 ) 10 (PO 4 )]·18H 2 O (Compound 1), [(CH 3 ) 2 NH 2 ] 1 Na 11 [Ni 2 Mo 8 O 22 (HPO 3 ) 10 ]·16H 2 O (Compound 2), Na 15 (OH) 5 [Mo 6 O 18 (HPO 3 ) 4 ] 2 [MoO] 1.5 ·16H 2 O (Compound 3), [(CH 3 ) 2 NH 2 ] 4 Na 11 [Na[Mo 6 O 15 (HPO 3 ) 4 ] 2 ]·18H 2 O (Compound 4), are successfully designed and synthesized via a microwave-assisted reaction protocol. Compounds 1–4 not only exhibit broad absorption and notable photothermal conversion effects in near-infrared (NIR) region, but also have high photothermal conversion efficiencies and high quality NIR photothermal imaging effects under NIR laser irradiation. Compound 1 shows the best photothermal conversion effect, and it provides a unique model to explore the relationship between the complex metal oxide structure and photothermal conversion behavior at the molecular level. Both the experimental results and theoretical calculations consistently conclude that the charge and degree of electron delocalization on the Cluster have a robust influence on the photothermal conversion, as well as the aggregation microstructures. Graphical abstract