Multifunctional Tetracene/Pentacene Host/Guest Nanorods for Enhanced Upconversion Photodynamic Tumor Therapy

The tissue penetration depth of light and the singlet oxygen (¹O₂) generation efficiency of photosensitizers (PSs) are the two main factors that determine the effectiveness of photodynamic therapy for tumors. Herein, we report a novel strategy to prepare a multifunctional upconversion photosensitizer (UCPS) based on the host/guest nanoarchitecture. By a simple reprecipitation method, host/guest tetracene/pentacene nanorods (Tc/Pc NRs) were synthesized for enhancing triplet-triplet annihilation-upconversion (TTA-UC) or two-photon excited emission and ¹O₂ generation efficiency upon 650 or 808 nm excitation. Tc/Pc NRs had higher ¹O₂ quantum yield (74%) than Tc NRs (28%) upon 650 nm laser irradiation. The proposed mechanism is that doping Pc molecules into Tc NRs induces intermediate states between S₀ and S₁, shortening the energy gap for ¹O₂ generation and resulting in TTA-UC emission. Equally important, with 808 nm fs laser excitation, Tc/Pc NRs showed an enhanced ¹O₂ generation efficiency and two-photon absorption cross section (σ) compared with Tc NRs. In addition, when the tumors in mice were exposed to Tc/Pc NRs with 650 or 808 nm wavelength irradiation, the tumor inhibition rates achieved 99 and 95%, respectively. This work opens new perspectives for exploring novel nano-UCPSs for biomedical applications.