Ultrafast excited state relaxation dynamics of pyran-based D-π-A systems: solvent polarity controls the triplet state.

The excited state relaxation dynamics of V-shaped D-π-A systems having 4H-pyranylidene appended barbituric acid as an acceptor and diphenylamine (TPAPBA) and diethyl amine (EAPBA) as donors were investigated using steady-state and time-resolved spectroscopy along with theoretical optimization. The steady-state photophysical characterization exhibited the bathochromic shift of the emission maximum (∼6400 cm-1) and large change in the dipole moment (∼24D) with an increase of solvent polarity, reflecting the occurrence of the intramolecular charge transfer state (ICT) in the excited state. The nanosecond and femtosecond transient absorption spectra of these derivatives in a non-polar solvent, toluene, reveal that the excited state relaxation pathway involving a local excited state (LE) decayed to ICT followed by the formation of a twisted ICT state by conformational relaxation, finally leading to the triplet state. The lack of observation of a triplet state in the polar solvent, acetonitrile, signifies that the relaxation dynamics of V-shaped triads in the excited state are influenced by the polarity of the solvent.

Antenna Effect in Noble Metal-Free Dye-Sensitized Photocatalytic Systems Enhances CO2 -to-CO Conversion.

Dye-sensitized photocatalytic systems (DSPs) have been extensively investigated for solar-driven hydrogen (H2 ) evolution. However, their application in carbon dioxide (CO2 ) reduction remains limited. Furthermore, current solar-driven CO2 -to-CO DSPs typically employ rhenium complexes as catalysts. In this study, we have developed DSPs that incorporate noble metal-free components, specifically a zinc-porphyrin as photosensitizer (PS) and a cobalt-quaterpyridine as catalyst (CAT). Taking a significant stride forward, we have achieved an antenna effect for the first time in CO2 -to-CO DSPs by introducing a Bodipy as an additional chromophore to enhance light harvesting efficiency. The energy transfer from Bodipy to zinc porphyrin resulted in remarkable stability (turn over number (TON)=759 vs. CAT), and high CO evolution activity (42 mmol g-1 h-1 vs. CAT).

Dye-Sensitized Photocatalysis: Hydrogen Evolution and Alcohol-to-Aldehyde Oxidation without Sacrifical Electron Donor.

There is a growing interest in developing dye-sensitized photocatalytic systems (DSPs) to produce molecular hydrogen (H2 ) as alternative energy source. To improve the sustainability of this technology, we replaced the sacrificial electron donor (SED), typically an expensive and polluting chemical, with an alcohol oxidation catalyst. This study demonstrates the first dye-sensitized system using a diketopyrrolopyrrole dye covalently linked to 2,2,6,6-tetramethyl-1-piperidine-N-oxyl (TEMPO) based catalyst for simultaneous H2 evolution and alcohol-to-aldehyde transformation operating in water with visible irradiation.