Achieving high singlet-oxygen generation by applying the heavy-atom effect to thermally activated delayed fluorescent materials

Abstract

A bromine-substituted thermally activated delayed fluorescent (TADF) molecule AQCzBr2 is designed with both small singlet-triplet splitting (ΔEST) and increased spin-orbit coupling (SOC) to boost intersystem crossing (ISC) for singlet oxygen...

Thermally Activated Delayed Fluorescence Material: An Emerging Class of Metal‐Free Luminophores for Biomedical Applications

“…Recently, to further improve the performance of TADF materials in PDT, Lee's group introduced heavy‐atom effect into the TADF molecule (AQCz) to construct AQCzBr 2 PSs, which displayed the boosted spin–orbit coupling (SOC) to increase the ISC progress, leading to a considerably high 1 O 2 quantum yield (91%). [ 154 ]…”

Target-Oriented Synthesis of Marine Coelenterazine Derivatives with Anticancer Activity by Applying the Heavy-Atom Effect

“…PDT consists of the irradiation of a tumor site, in which a photosensitizer is accumulated, with light of a specific wavelength. Upon photoexcitation, the photosensitizer will be excited from its ground state (S 0 ) to its lowest singlet excited state (S 1 ) and will undergo intersystem crossing (ISC) to triplet states (T 1 ), now capable of sensitizing the highly cytotoxic singlet oxygen after reacting with triplet oxygen [1,3]. Unfortunately, the low penetration of light into biologic tissues limits this therapy to the treatment of superficial tumors or tumors on the outer lining of internal organs and cavities [4,5].…”

“…Enhancing the S0 → T1 ISC pathway can then enable the use of the chemiluminescent reaction of Clz as a self-excitation mechanism to directly generate triplet states able to sensitize singlet oxygen, thus leading to a light-free intracellular reaction exclusively triggered by a cancer marker (superoxide anion). One of the most effective strategies to enhance the efficiency of ISC pathways is through the heavy-atom effect (e.g., introduction of halogen atoms) [3]. Accordingly, we recently synthesized 6-(4bromophenyl)-2-methylimidazo [1, 2−a] pyrazin-3(7H)-one (Br-Cla) (Scheme 1a), a Enhancing the S 0 → T 1 ISC pathway can then enable the use of the chemiluminescent reaction of Clz as a self-excitation mechanism to directly generate triplet states able to sensitize singlet oxygen, thus leading to a light-free intracellular reaction exclusively triggered by a cancer marker (superoxide anion).…”

“…Accordingly, we recently synthesized 6-(4bromophenyl)-2-methylimidazo [1, 2−a] pyrazin-3(7H)-one (Br-Cla) (Scheme 1a), a Enhancing the S 0 → T 1 ISC pathway can then enable the use of the chemiluminescent reaction of Clz as a self-excitation mechanism to directly generate triplet states able to sensitize singlet oxygen, thus leading to a light-free intracellular reaction exclusively triggered by a cancer marker (superoxide anion). One of the most effective strategies to enhance the efficiency of ISC pathways is through the heavy-atom effect (e.g., introduction of halogen atoms) [3]. Accordingly, we recently synthesized 6-(4-bromophenyl)-2-methylimidazo [1, 2−a] pyrazin-3(7H)-one (Br-Cla) (Scheme 1a), a brominated Clz derivative in which the hydroxyl of the phenol group was substituted by bromine, and the p-cresol and benzyl moieties of Clz were replaced by a methyl group and a hydrogen atom, respectively [12].…”

Photoswitchable Thermally Activated Delayed Fluorescence Nanoparticles for “Double‐Check” Confocal and Time‐Resolved Luminescence Bioimaging

“…[27][28][29][30] TADF luminophores with relatively small singlettriplet splitting energy (ΔE ST ) can not only achieve efficient reverse intersystem crossing (RISC) at room temperature from the lowest excited triplet state (T 1 ) to the lowest excited singlet state (S 1 ), but also exhibit longer lifetimes ranging from nanoseconds to milliseconds than the prompt fluorescence (<10 ns) of the traditional fluorophores, which offers an alternative method to increase the signal-to-noise ratio for TRLI. [31][32][33] However, oxygen-sensitivity and hydrophobicity of TADF emitters greatly hinders their application in bioimaging. [34,35] The delayed fluorescence polymeric nanoparticles (DFPNs) are emerging as a new class of nanoprobes for TRLI due to their excellent water-dispersibility, prominent photostability, Thermally activated delayed fluorescence (TADF) materials have attracted increasing attention due to their great potential in time-resolved luminescence imaging (TRLI) in bioimaging.…”