Porphyrin is an essential compound used in nature: processes like photosynthesis and oxygen fixation on blood are assisted by porphyrins. Scientists (chemists, physicists, engineers, and others) are also exploiting porphyrins for artificial photosynthesis and energy generation, pigments and catalysts, given their success in nature. Among the most studied porphyrins is the octaethylporphyrin class (commonly used as a benchmark compound for study), containing eight ethyl radicals attached to the main ring. Those molecules are reported to have a fast internal conversion from the first excited singlet state to the second singlet and subsequentially a cascade decay passing through the triplet state and eventual return to the ground state. Artificial porphyrins sent by Prof Bruecker, University of Connecticut, could share vital information about tuning the photophysical properties of porphyrins. We studied these molecules using ultrafast time-resolved spectroscopy and mapped the energy decay within the set, finding a significant decrease in lifetime (146 microseconds for H2OEP to 22 microseconds for 2,13-dioxoisobacteriochlorin) for internal conversion and intersystem crossing going from H2OEP to Isobacteriochlorins. Dr Cardozo from UFRJ supported the finding with computational calculations, establishing a relationship between carbonyl deformations and spin-orbit coupling.
The world worries about disease spread are in the spotlight once again. This body of work investigates a practical and low-cost way to sterilize medical tools is thus investigated in this body of work. Metal oxides are well known and explored by their antibacterial properties by triggering a chain reaction upon light exposition. We investigated these films' photophysical and chemical properties alongside their antibacterial efficiency. The samples were provided by Dr Sami Rtimi (EPFL), who synthesised metal oxide films and double metal oxide films. We use several methods of characterisation to map electronic and structural properties. XPS results elucidate the atomic composition and bonding between the atoms in the films, quantifying the composition, whereas AFM shows the samples’ surface area and thickness. In both sets of samples, it became clear that the mix of oxides (Copper-Iron and Copper-Titanium) is more effective in killing bacteria, as shown by experiments provided by Dr Rtimi. Transient absorption data show a decrease in overall lifetime when comparing the pure oxides with the mixed ones. We also show that the metal in the mixed oxides is relevant and interferes with how the decaying pathway occurs. The titanium-copper sample has different TA spectra depending on the film composition: the signal is mostly copper in the 20% Titanium and 80%
copper. When the amount of titanium increases, 60% titanium and 40% copper, the spectra show both copper and titanium features, suggesting some interplay between these atoms. Finally, a comprehensive understanding of reactive oxygen species generation and photophysical properties are achieved.
