Pentacene Nanorods as Effective Photosensitizer for Photodynamic Therapy of Tumor via Singlet Fission

Abstract

AbstractSinglet fission (SF), whereby a singlet exciton is converted into a pair of triplet excitons, can improve the efficiency of solar cells. Pentacene has been extensively studied as the most promising SF compound, owing to its 200% yield of triplet states. However, the easy degradation of pentacene in the presence of light and air owing to photooxidation cannot be explained by the classical 1O2 generation mechanism. To address this issue, in the present study, pentacene nanorods (Pc NRs) are prepared as a novel photosensitizer (PS); self‐carried Pc NRs exhibited higher 1O2 generation capacity. Thus, a novel 1O2 generation mechanism is proposed based on the SF effect. The initial photon absorption occurs to access single‐exciton states, S1–S3. Excited‐state Pc pairs accelerate the SF effect in pentacene NRs, leading to a non‐adiabatic transition to the dark D state. Dark D state is a singlet state by two triplets coupled overall, and it can transfer its energy to 3O2 for generating 1O2. Using Pc NRs as PSs, photodynamic therapy (PDT) inhibits tumor growth in 4T1 tumor‐bearing mice upon 405‐nm‐wavelength and 650‐nm‐wavelength laser irradiations. This study paves the way to discover novel PSs that are not considered with classical 1O2 generation mechanisms.