Michael Towrie

Photoelectron spectroscopy of S1 toluene: II. Intramolecular dynamics of selected vibrational levels in S1 toluene studied by nanosecond and picosecond time-resolved photoelectron spectroscopies

We present results which suggest that the photophysics of S(1) toluene is significantly more complicated than that of the related molecules p-fluorotoluene or p-difluorobenzene. We have measured a range of photoelectron spectra for a number of S(1) internal energies, on different time scales and at different temperatures, in an attempt to unravel the competing processes, but the final conclusion remains outstanding.

Mapping out the key carbon–carbon bond-forming steps in Mn-catalysed C–H functionalization

AbstractDetailed understanding of the mechanistic processes that underpin transition metal-catalysed reactions allows for the rational and de novo development of complexes with enhanced activity, efficacy and wider substrate scope. Directly observing bond-cleaving and -forming events underpinning a catalytic reaction is non-trivial as the species that facilitate these steps are frequently short-lived and present at low concentrations. Here, we describe how the photochemical activation of a manganese precatalyst, [Mn(ppy)(CO)4] (ppy = 2-phenylpyridine), results in selective loss of a carbonyl ligand simulating entry into the catalytic cycle for manganese-promoted C–H bond functionalization. Time-resolved infrared spectroscopy (on the ps–ms timescale) allows direct observation of the species responsible for the essential C–C bond formation step and an evaluation of the factors affecting its rate. This mechanistic information prompted the discovery of a new photochemically initiated manganese-promoted coupling of phenylacetylene with 2-phenylpyridine. This study provides unique insight into the mechanistic pathways underpinning catalysis by an Earth-abundant metal, manganese.Although mechanistic understanding can drive new reactivity development, the key bond-forming and -breaking steps in catalytic cycles are often sufficiently fast to elude observation. Here, the authors photochemically produce a key intermediate in Mn-catalysed C–H functionalization, and follow the subsequent steps—spanning processes occurring over seven orders of magnitude in time—using time-resolved infrared spectroscopy.n

Bound Water is Central to Both Molecular Recognition and Function in the Catalase Enzyme SUPPORTING INFORMATION

Department of Physics, University of Strathclyde, 107 Rottenrow East, Glasgow, G4 0NG, United Kingdom, Diamond Light Source, Harwell Science and Innovation Campus, Didcot, OX11 0QX, United Kingdom Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, 161 Cathedral Street, Glasgow, G4 0RE, United Kingdom, School of Biological Sciences, University of East Anglia, Norwich, NR4 7TJ, United Kingdom, Central Laser Facility, Research Complex at Harwell, Rutherford Appleton Laboratory, Didcot, OX11 0QX, United Kingdom Correspondence email: neil.hunt@strath.ac.uk

A photophysical study of substituted arylethynylenes

A study of a group of compounds based on the 1,4-bis(phenylethynyl)benzene (1) architecture was undertaken to improve our understanding of their photophysics and the factors which control their geometry and hence the π- conjugation pathway in the ground and excited state of these compounds. 1 exists as a range of molecular rotamers in the ground state, resulting from the low barrier to rotation around their C(sp)-C(sp2) bonds. These compounds are highly conjugated systems with good electron conducting properties, due to delocalisation of the HOMO and LUMO over the molecule. In the electronic excited state they are capable changing their molecular conformation and will adopt a planar, or near planar, low energy conformation prior to fluorescence emission in solution. In a glassy matrix at 77 K with sterically hindering substituents on the benzene rings of 1, emission form high and low energy conformations are observed. 1 is highly emissive owing to the high oscillator strength of the S1→S0 transition. All the compounds studied maintained their C≡C character in the excited singlet and triplet states. The substitution of the central benzene ring in 1 with a thiophene moiety increases the singlet oxygen generation quantum yield, which is consistent with greater intersystem crossing to the triplet excited state.