Octahedral chromium(III) complexes and their photophysical properties

Abstract

The push for increased sustainability in recent times has resulted in a desire for more earth-abundant alternatives to precious metal-containing photoactive transition metal complexes, including the well-established d^{6 3}MLCT-emitter complexes of ruthenium(II), osmium(II), iridium(III) etc. This has reinvigorated research into octahedral complexes of chromium(III), amongst other first row transition metal complexes, for their luminescence and excited state redox  properties.

Reported herein is the preparation and characterisation of multiple novel octahedral chromium(III) complexes, along with steady-state and time-resolved photophysical studies to probe their excited state dynamics. This includes homoleptic  1,2,3-triazolylcontaining chromium(III) complexes, of which one was studied using fluorescence upconversion spectroscopy to directly determine the rate of inter-system crossing from the quartet to doublet excited states for the first time.  Chromophoric pyridyl-imine and Ar-BIAN ligands were also used in heteroleptic chromium(III) complexes in attempts to boost absorption within the visible region, and achieve luminescence from visiblelight excitation. The redox non- innocence and rich electrochemistry of the chromium(III) Ar-BIAN complexes were explored spectroscopically. Also, the first homoleptic N-heterocyclic and mesoionic carbene chromium(III) complexes were prepared using ligands bearing  imidazolylidene and 1,2,3-triazolylidene donors, and their photophysical properties and excited state dynamics were studied and compared using ultrafast transient absorption spectroscopy. The varying nephelauxetic parameters of the  different carbene donors allowed tuning of the spin-flip emission energy within the NIR region.

Date of Award	21 Dec 2023
Original language	English
Supervisor	Paul Elliott (Main Supervisor) & Paul Scattergood (Co-Supervisor)