Acceptor-donor-acceptor-type Molecules with large electrostatic potential difference for Effective NIR Photothermal Theranostics

Although acceptor-donor-acceptor (A-D-A)-type molecules show advantages in constructing NIR absorbing photothermal agents (PTAs) due to their strong intramolecular charge transfer and molecular planarity, their applications in photothermal therapy (PTT) of tumor are insufficiently explored. In particular, the influence of ESP distribution on optical properties of A-D-A photosensitizers has not been investigated. Herein, we utilized the advantages of A-D-A-type molecules with large ESP difference to construct NIR absorbing PTA with sufficient extinction coefficient (ɛ) and high photothermal conversion efficiency (PCE). The calculation results of density functional theory (DFT) indicate that the large ESP difference of Y6 may increase intermolecular interactions and induce tight packing of the A-D-A photosensitizer. As a result, Y6 NP exhibited an obvious bathochromic shift of absorption peak from 711 nm to 822 nm, with a NIR-II emission extended to 1400 nm. Moreover, a sufficient ɛ of 3.34 L·g-1·cm-1 and PCE of 66.3% were attained, making Y6 NP suitable for PTT. With a concentration of 100 μg/mL, Y6 NPs in aqueous dispersion yielded a death rate of 93.4% for 4T1 cells upon an 808 nm laser irradiation (1 W·cm-2) for 10 min, which is comparable with the best results of recently reported PTT agents.