Carbazolyl dicyanobenzene (CDCB) derivates exhibiting thermally activated delayed fluorescence (TADF) have shown themselves to be excellent photocatalysts over recent years, particularly 4CzIPN, although investigation into organic TADF compounds as photocatalysts outside of the CDCB group has been limited. Herein, we report an alternative donor−acceptor TADF structure, 9,9′-(sulfonylbis(pyrimidine-5,2-diyl))bis(3,6-di-tert-butyl-9H-carbazole), pDTCz-DPmS, for use as a photocatalyst (PC). A comparison of the electrochemical and photophysical properties of pDTCz-DPmS with 4CzIPN in a range of solvents identifies the former as a better ground state reducing agent and photoreductant, while both exhibit similar oxidation capabilities in the ground and excited state. The increased conjugation of pDTCz-DPmS relative to 4CzIPN presents a more intense CT band in the UV−vis absorption spectrum, aiding in the light absorption of this molecule. Prompt and delayed emission lifetimes are observed for pDTCz-DPmS, confirming the TADF nature, both of which are sufficiently long-lived to participate in productive photochemistry. These combined properties make pDTCz-DPmS useful in photocatalysis reactions, covering a range of photoredox oxidative and reductive quenching reactions, as well as those involving a dual Ni(II) cocatalyst, alongside energy transfer processes. The higher triplet energy and increased photostability of pDTCz-DPmS compared with 4CzIPN were found to be advantages of this organic PC.
Phototherapies, in the form of photodynamic therapy (PDT) and photothermal therapy (PTT), are very promising treatment modalities for cancer since they provide locality and turn-on mechanism for toxicity, both of which are critical in reducing off-site toxicity. Irradiation of photosensitive agents demonstrated successful therapeutic outcomes; however, each approach has its limitations and needs to be improved for clinical success. The combination of PTT and PDT may work in a synergistic way to overcome the limitations of each method and indeed improve the treatment efficacy. The development of single photosensitive agents capable of inducing both PDT and PTT is, therefore, extremely advantageous and highly desired. Cyanine dyes are shown to have such potential, hence have been very popular in the recent years. Luminescence of cyanine dyes renders them as phototheranostic molecules, reporting the localization of the photosensitive agent prior to irradiation to induce phototoxicity, hence allowing image-guided phototherapy. In this review, we mainly focus on the cyanine dye–based phototherapy of different cancer cells, concentrating on the advancements achieved in the last ten years.
The stability of a photocatalyst under irradiation is important in photoredox applications. In this work, we investigated the stability of a thermally activated delayed fluorescence (TADF) photocatalyst {3DPAFIPN [2,4,-5-fluoroisophthalonitrile]}, recently employed in photoredox-mediated processes, discovering that in the absence of quenchers the chromophore is unstable and is efficiently converted by irradiation with visible light into another species based on the carbazole-1,3-dicarbonitrile moiety. The new species obtained is itself a TADF emitter and finds useful applications in photoredox transformations. At the excited state, it is a strong reductant and was efficiently applied to cobalt-mediated allylation of aldehydes, whereas other TADFs (4CzIPN and 3DPAFIPN) failed to promote efficient photocatalytic cycles.
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