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.

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.

General methods S3Materials S3Optimization of the enantioselective photo alkylation of aldehydes S4Light/dark effect S7 Synthesis of catalyst 3 S8 Synthesys of aldehydes 1g,h S8General procedure for enantioselective photo alkylation of aldehydes. S9General procedure for determination of enantiomeric excesses of compounds 6-9. S10 Characterization data of compounds 4-15 S11Synthesis of (-)-isodeoxypodophyllotoxin S14 Mechanistic insights. S15Synthesis of aldehyde (±)-trans 1i. S15 Synthesis of aldehyde (±)-cis 1i. S16 Photoalkylation of aldehyde (±)-trans-1i. S17Photoalkylation of aldehyde (±)-cis-1i. S24 Photophysical measurements. S28Emission profile of the 23W Compact Fluorescent lamp used to irradiate the solutions. S32EPR studies S33 References. S34Copies of NMR spectra. S36Copies of HPLC, GC traces and NMR spectra for the determination of enantiomeric excess. S56S3

The goal of this paper concerns the first evaluation of two recently reported coumarins to initiate photopolymerization reactions.

A gas-phase nitrogen-nitrogen noncovalent interaction has been unveiled in the nitroethane-trimethylamine complex in an environment free from solvent and matrix effects using rotational spectroscopy in supersonic expansion. Different quantum chemical models (NOCV/CD and NBO) agree in indicating that this interaction largely prevails over the C-H⋅⋅⋅O and C-H⋅⋅⋅N hydrogen bonds. Furthermore, a SAPT analysis shows that electrostatic and dispersion interactions play a comparable role in stabilizing the complex. The conformational landscape exploration and stationary points characterization have been performed using state-of-the-art quantum-chemical computations providing significant insights on structure determination.