BODIPYs offer a versatile platform to build organic triplet photosensitisers for PDT, TTA upconversion and photocatalysis. Tuning their properties provides the opportunity of replacing heavy-metal complexes and can lead to improved sustainability.

The goal of this paper concerns the first evaluation of two recently reported coumarins to initiate photopolymerization reactions. These two compounds (CoumA and CoumB) are proposed as high performance visible light photoinitiators and evaluated as photoredox catalysts (PCs), in the presence of an iodonium salt or with an amine, for both the free radical polymerization (FRP) of (meth)acrylates and the cationic polymerization (CP) of epoxides upon visible light exposure using an LED at 405 nm. These coumarin derivatives showed a high photoinitiation ability i.e. excellent polymerization rates and high final monomer conversions were obtained. The photophysical and photochemical properties of the coumarin derivatives were studied in terms of absorption, steady state photolysis and fluorescence spectroscopy. The photoinitiation mechanisms of the coumarin derivatives were discussed from fluorescence quenching, redox behavior and cyclic voltammetry experiments. A full picture of the involved photochemical mechanisms is provided. Coumarin-based systems are high performance photoinitiators, and their use in new photosensitive 3D printing resins will also be presented. Remarkably, CoumB is also found to be very efficient for the preparation of hydrogels under mild conditions due to its high solubility in water i.e. CoumB corresponds to a high-performance water soluble photoinitiator. Finally, the usage of the new coumarin derivatives for photocomposite synthesis with glass fibers (thick samples with a good depth of cure) using a near-UV conveyor (LED @395 nm) is particularly outlined.

A mechanism based on the sequential absorption of two photons by the components of a redox couple has been recently proposed for catalysis of the energetically demanding reduction of aryl halides. Here, we analyze the suggested photochemical mechanism of this reaction, which employs perylenediimide (PDI) as a photocatalyst, on the basis of spectroscopic, electrochemical and electron paramagnetic resonance data. Our results indicate that the photoexcited PDI radical anion (*PDI˙⁻) cannot play the role of a photosensitizer in the aforementioned process. Instead, the reduction of 4′-bromoacetophenone likely involves *PDI˙⁻ decomposition products. The extremely short lifetime of the photoexcited transient species, as *PDI˙⁻, is a major general limitation for photocatalytic schemes based on sequential two-photon excitation. In order to better understand the potential of such schemes, we discuss them in the context of the Z-scheme in natural photosynthesis.

A Barbier-type Cp2TiCl2-mediated (10 mol%) photoredox allylation of aldehydes under irradiation with visible light (blue LEDs, 450 nm) and in the presence of an organic dye (3DPAFIPN, 5 mol%) with allylbromides is described.

Using ascorbate as a sacrificial reductant, iodo-Bodipy dye 1b is able to promote the ATRA reaction between bromoderivatives and alkenes. This finding expands the possibility of using Bodipy dyes to promote photocatalytic reactions in efficient ways.