Photophysics of bismuth coordination complexes for optoelectronics Harsh Bhatia and Bob C. Schroeder University College London, UK
Bismuth based materials have been the focus of the scientific community for decades and these materials are extensively studied for the applications of medicinal chemistry, 1 and material chemistry 2,3 in the form of complexes, oxides, nanoparticles and perovskites. However, the coordination complexes of the bismuth are not well explored while the complexes of 1 st and 2 nd row transition metal atoms have been the focus for long to harness solar light and generate excitons in OLEDs. These complexes are well explored but many of the metal atoms are expensive, toxic, and suffer from various problems. Due to which a non-toxic and easily available substitute of transition metal is required without compromising the efficiency. Therefore, to replace transition metal complexes with bismuth for applications in material sciences, here we explore the fundamental optoelectronics properties of bismuth-based coordination complexes. In this work, we studied the detailed optical properties and photophysics of BiCl 3 , BiBr 3 and BiI 3 based coordination complexes. The complexes consist of halides (Chlorine, Bromine and Iodine) as ancillary ligand and thiophene substituted phenanthroline as the main ligand attached to the bismuth atom in bi-octahedron coordination geometry. The complexes are designed to push the electron density and shift the absorption of the complexes to visible region. The effect of the difference in electronic density with the variation of ancillary ligand in the complexes is explored in the ground state (G.S.) and excited state (E.S.) of the complexes via different spectroscopic tools: UV-Vis absorption, photoluminescence spectroscopy, lifetime measurements and nanosecond transient absorption spectroscopy (TAS). To further support the experimental data, DFT and TD-DFT studies were carried out to understand the effect of variation in the ancillary ligand over the G.S. and E.S. properties. The change in the ancillary ligand from chlorine, bromine to iodine bathochromically shifts the tail of the absorption band and leads to the formation of a new lower energy band at ~500 nm in BiI 3 complex. The comparison of the absorption properties shows that complex with Iodine as ancillary ligand have profound effect over the absorption and lead to high absorption coefficient of 46000 M -1 cm -1 . The photophysical analysis further shows that excited state of all the complexes decay with the similar lifetimes (t(Chloro) = 0.32,0.47 ns, t(Bromo) = 0.38,0.53 ns t(Iodo) = 0.36,0.5 ns) when compared with ligand (t(ligand) = 0.39, 0.6 ns) and the complexes emit at same wavelength (465 nm) as ligand. The measurements confirm that excited state properties of the complexes are ligand centred (LC) and independent of the inorganic part of the complexes. Additionally, the similar LC excited state behaviour of the complexes was further proved by nsTAS measurements. These detailed photophysical and theoretical analysis confirms that inorganic part of the complexes plays no role to govern the lowest energy E.S. properties while G.S. properties of the complexes are extensively influenced by the inorganic half. These results demonstrate that choice of inorganic part in bismuth coordination complexes can dramatically alter the photophysical properties of the complexes hence the application can be tuned from OLEDs to photovoltaics. References 1. Griffith, D. M.; Li, H., Werrett, M. V.; Andrews, P. C.; Sun, H. Soc. Rev. 2021 , 50 , 12037-12069. 2. Bothwell, J. M.; Krabbe, S. C.; Mohan, R. S. Chem. Soc. Rev. 2011 , 40 , 4649-4707. 3. Sun, H-. T.; Zhou, J.; Qiu, J.; Mater. Sci. 2014 , 64 , 1-72.
PFS01
© The Author(s), 2023
Made with FlippingBook Learn more on our blog