Reviewing the evolutive ACQ‐to‐AIE transformation of photosensitizers for phototheranostics

Abstract

Photodynamic therapy (PDT) represents an emerging noninvasive treatment technique for cancers and various nonmalignant diseases, including infections. During the process of PDT, the physical and chemical properties of photosensitizers (PSs) critically determine the effectiveness of PDT. Traditional PSs have made great progress in clinical applications. One of the challenges is that traditional PSs suffer from aggregation‐caused quenching (ACQ) due to their discotic structures. Recently, aggregation‐induced emission PSs (AIE‐PSs) with a twisted propeller‐shaped conformation have been widely concerned because of high reactive oxygen species (ROS) generation efficiency, strong fluorescence efficiency, and resistance to photobleaching. However, AIE‐PSs also have some disadvantages, such as short absorption wavelengths and insufficient molar absorption coefficient. When the advantages and disadvantages of AIE‐PSs and ACQ‐PSs are complementary, combining ACQ‐PSs and AIE‐PSs is a “win‐to‐win” strategy. As far as we know, the conversion of traditional representative ACQ‐PSs to AIE‐PSs for phototheranostics has not been reviewed. In the review, we summarize the recent progress on the ACQ‐to‐AIE transformation of PSs and the strategies to achieve desirable theranostic applications. The review would be helpful to design more efficient ACQ‐AIE‐PSs in the future and to accelerate the development and clinical application of PDT.

Bright and White Light-Triggered Aggregation-Induced Emission Nanoparticles Prepared in Miniemulsions for Photodynamic Theranostics

“…Photodynamic therapy (PDT) excited by visible light or near-infrared light has been widely applied for cancer treatments, taking advantage of its high spatiotemporal precision, noninvasiveness, and low multidrug resistance. − Photosensitizers (PSs), as the cornerstone of PDT, are photoexcited to the singlet excited state (S 1 ), generating S 1 excitons, transiting to the triplet excited state (T 1 ) via the intersystem crossing (ISC) process, and undergoing type I (electron transfer) or type II (energy transfer) photochemical paths to produce highly cytotoxic reactive oxygen species (ROS), including hydroxyl radicals (HO·), superoxide radicals (O 2 •– ), and singlet oxygen ( 1 O 2 ), for destruction of targeted cells or tissues. − In contrast to traditional aggregation-caused quenching (ACQ) PSs, aggregation-induced emission (AIE) PSs hold stronger ability to generate ROS in the concentrated or confined environments, thanks to the suppressed nonradiative pathway. − More promisingly, simultaneously emitting fluorescence and producing ROS make AIE PSs capable of fluorescence imaging-guided PDT, thereafter visualizing the position of drugs and tumors and performing noninterventional treatments with high spatial and temporal precision. − …”

Aggregate-state-dependent photochromism and circularly polarized luminescence of a chiral biquinoline amphiphile

“…2 Another well-known example is the luminescence change of a luminophore upon aggregation, 3 where two distinct phenomena have been observed by scientists, i.e. , aggregation-caused quenching 4 and aggregation-induced emission. 5 The aggregation or self-assembly of chiral π-systems has been proven to be an effective method to fabricate chiral materials based on various non-covalent interactions, such as hydrogen-bonding, π–π stacking and van der Waals forces.…”

Molecularly Engineered Near-Infrared Aggregation-Induced Emission Photosensitizer for In Situ-Activated Light Irradiation-Free Photodynamic Therapy

“…8,9 Traditional PSs, such as cyanine and porphyrin, often suffer from aggregation-caused quenching (ACQ) when aggregated, reducing their ability to generate cell-killing ROS. 10 Aggregation-induced emission (AIE) PSs, on the other hand, exhibit weak or no fluorescence and a low generation of ROS in solutions but demonstrate strong fluorescence and ROS generation in the aggregated state, thereby avoiding selfquenching. The development of AIE PSs with near-infrared (NIR) emission (650−900 nm) facilitates the advancement of image-guided PDT.…”