Activated photothermal heating using croconaine dyes
Graeme T. Spence, Gregory V. Hartland and Bradley D. Smith
Laser-induced photothermal heating is promoted by dyes or nanoparticles that strongly absorb light and
convert it into heat. The best known near-infrared absorbing systems are gold nanorods and nanocages.
The alternative strategy of using organic dyes to absorb the laser light has several inherent advantages
due to the small molecular size and potential synthetic flexibility, but a major drawback is rapid
photothermal bleaching. Here, we report three important findings: (a) near-infrared croconaine dyes
exhibit outstanding properties for high performance photothermal heating; including an intense and
narrow absorption band at around 800 nm, high chemical, photo- and thermal stability, very efficient
relaxation to the ground state, and very low oxygen photosensitization ability. (b) Photothermal heating
obeys the Beer–Lambert law (1 10A) and sample heating reaches an asymptotic limit when
chromophore absorbance values are greater than 1. (c) Croconaine dyes form red-shifted
encapsulation complexes which allows the realization of molecular recognition induced activated
photothermal heating, a broadly applicable nanoscale design concept that employs chemical or
supramolecular processes to switch on laser-induced hyperthermia.