Abstract
Deciphering singlet-to-triplet intersystem crossing (ISC) in organic near-infrared photosensitizers (PSs) is of fundamental importance in the designing of high-performance PSs to boost the clinical usage of photodynamic therapy (PDT). However, in-depth investigations of the ISC dynamics in near-infrared PSs have not been performed to date. Here, systematical investigations of the ISC dynamics in organic near-infrared BODIPY derivatives are presented, in which a multi-channel yet remarkably efficient ISC process is revealed by ultrafast femtosecond transient absorption (fs-TA) spectroscopy and theoretical calculation. The fs-TA verifies an exceptionally enhanced ISC efficiency (Φ ISC = 91%) in iodine-substituted BODIPY (2I-BDP) which is further supported by the calculation results. This endows 2I-BDP with an ultrahigh singlet oxygen quantum yield (Φ Δ = 88%), thus enabling a proof-of-concept application of highly efficient PDT in vivo under ultralow near-infrared light power density (10 mW cm-2). The in-depth understanding of ISC dynamics in organic near-infrared materials may provide valuable guidance in the designing of novel organic theranostic materials for clinical cancer treatment.
Highlights
Photodynamic therapy (PDT) is a rapidly developed, clinically approved therapeutic modality which utilizes the photoexcitation of an external photosensitizer (PS) by appropriate light to produce a highly localized cytotoxicity toward malignant cells.[1,2,3] Typically, the photodynamic therapy (PDT) efficiency highly relies on the singlet oxygen (1O2) quantum yield (FD) of the PS.[4]
Deciphering singlet-to-triplet intersystem crossing (ISC) in organic near-infrared photosensitizers (PSs) is of fundamental importance in the designing of high-performance PSs to boost the clinical usage of photodynamic therapy (PDT)
Systematical investigations of the ISC dynamics in organic nearinfrared BODIPY derivatives are presented, in which a multi-channel yet remarkably efficient ISC process is revealed by ultrafast femtosecond transient absorption spectroscopy and theoretical calculation
Summary
Power density (>100 mW cmÀ2) and greatly impede the practical application of PDT.[7,8] simultaneously intensifying the NIR absorption and amplifying the VD of nearinfrared PSs is urgently desirable to boost the practical application of PDT. In-depth investigations of the ISC dynamics in near-infrared PSs have not been performed to date, incorporating heavy metals (e.g., Ru or Ir) or special organic moieties (e.g., aromatic aldehydes and halogens) into chromophores was used to improve FD.[11] In addition, the as-prepared metal-containing complexes generally possess inherent drawbacks of extremely high cost and unknown heavy metal-induced toxicity concerns,[12] which is obviously unfavorable for clinical usage of PDT application In view of these drawbacks, despite the unsatisfactory FD,[13] recently organic NIR-absorptive materials have become an attractive candidate as PSs for PDT owing to their good biocompatibility, biodegradability, and structural exibility.[7,8,14,15] Given that, it will become necessary to decipher the underlying ISC dynamics in organic near-infrared materials to boost the development and clinical usage of PDT. Such a remarkably enhanced FISC endows 2I-BDP with an ultrahigh singlet oxygen quantum yield (FD 1⁄4 88%), enabling a proof-of-concept application of highly efficient PDT in vivo under ultralow near-infrared light power density (
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