Ground and Excited State Electronic Structures of d 8 -Squared Planar Platinum(II) and Gold(III) Complexes Bearing Cyclo
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Ground and Excited State Electronic Structures of d8-Squared Planar Platinum(II) and Gold(III) Complexes Bearing Cyclometallated 2,6-Diphenylpyridine and Pyrene-Derived N-Heterocyclic Carbene Nguyen Van Haa, * and Doan Thanh Data aFaculty
of Chemistry, VNU University of Science, Vietnam National University, Hoan Kiem, Hanoi, 110403 Vietnam *e-mail: [email protected] Received February 12, 2020; revised February 12, 2020; accepted April 3, 2020
Abstract—Electronic structures of four pyrene-derived N-heterocyclic carbene complexes of platinum(II) and gold(III) bearing cyclometallated 2,6-diphenylpyridine have been investigated theoretically. The structures of all complexes in gas phase have been first optimized. Different functionals and basis sets have been tested to find the best theoretical method. The results show that B3PW91 (LANL2DZ/6-31G*) combination give the best description of the molecules as compared with experimentally determined structural features. Using the calculation data from that best functional and mixed basis set combination, frontier molecular orbitals of the complexes have been examined. To gain understanding on the nature of electronic transitions in the UV-vis absorption spectra of the compounds, TD-DFT calculations have been carried out. A details analysis of the vertical excitation reveals that the nature of all the vertical electronic transitions in the complexes. Notably, the lowest energy transitions are πcb + dPt → π*cb (for Pt1 and Pt2) and πCNC → dAu + π*CNC (for Au1 and Au2) charge transfer in nature. A sharp contrast in lowest energy triplet excited state for d8-squared planar Au1 and Pt1 has been demonstrated. While no contribution from gold(III) d orbital to the SOMO and SOMO – 1 orbital of Au1, there is significant contribution of platinum(II) dyz orbital in the SOMO – 1 orbital of Pt1, suggesting possible interaction of this singly occupied orbital with radical of π-symmetry substrates. Keywords: N-heterocyclic carbene, cyclometallated Pt(II) and Au(III), electronic property, UV-vis absorption spectroscopy, lowest energy triplet excited state DOI: 10.1134/S0036023620110145
INTRODUCTION In the past few decades, N-heterocyclic carbene (NHC) has undoubtedly becoming an essential class of ligand in organometallic chemistry [1–7]. Due to their excellent steric and electronic turnability [8, 9], NHC transition metal complexes are now found potential applications in various areas, such as drug development, catalysis and advanced material development, including light absorbing and emitting materials [1–4, 10–14]. In parallel, luminescent transition metal complexes have recently attracted a lot of attention due to their potential application in many processes, such as light emitting material, bioimaging, photocatalysis [15–23]. Among the various platforms, d8 squared planar cyclometallated platinum(II) and gold(III) stand out as one of the better choice since the complexes usually highly emissive with long excited state lifetime [24–27].
Despite the success of two
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