Chalcogen modification: one-step strategy for tuning the photophysical properties and NIR phototherapy of iodinated BODIPY†

Near-infrared (NIR) photosensitizers have immense potential for in vivo phototherapy due to minimal scattering of NIR light in biological tissues. Among various types of photosensitizers, BODIPY dyes are potential candidates for phototherapy owing to their high molar extinction coefficient and tunable photophysical properties. However, most NIR BODIPY photosensitizers have relatively complicated structures and lengthy synthesis approaches, restricting their practical application. In this work, a simple strategy of chalcogen modification was applied to tune the photophysical properties of iodinated BODIPY for enhanced NIR phototherapy. As the atomic radius of chalcogen atoms increases, the BODIPY-X (X = O, S, Se, and Te) dyes exhibit a red-shifted absorption from 558 nm, 610 nm, and 618 nm to 660 nm, a faster singlet oxygen generation rate, and higher photothermal conversion efficiency due to the heavy atom effect. This modification facilitates intramolecular charge transfer (ICT) and enhances intersystem crossing (ISC), critical for effective PDT and PTT. To improve hydrophilicity and delivery efficiency, we encapsulated BODIPY-X using the amphiphilic copolymer Pluronic F127, creating F127/BODIPY-X nanoparticles (NPs). These NPs exhibited enhanced solubility and bioavailability, crucial for therapeutic efficacy. Moreover, the F127-encapsulated BODIPY-Te nanoparticles exhibit the best anti-tumor efficiency on U87-bearing mice, which is consistent with their outstanding photothermal conversion and photodynamic performance. Hence, a chalcogen modification strategy with a simple synthesis approach paves a new way for tuning the photophysical properties of NIR photosensitizers and could stimulate the rapid development of NIR phototheranostic agents.