Vol.:(0123456789) 1 3 Theoretical Chemistry Accounts (2018) 137:180 https://doi.org/10.1007/s00214-018-2396-8 REGULAR ARTICLE Structural, optical and nonlinear optical properties and TD‑DFT analysis of heteroleptic bis‑cyclometalated iridium(III) complex containing 2‑phenylpyridine and picolinate ligands Djebar Hadji 1  · Houari Brahim 1 Received: 30 August 2018 / Accepted: 20 November 2018 / Published online: 23 November 2018 © Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract In this work, we studied the structural, optical and nonlinear optical properties and UV–visible absorption spectrum of the heteroleptic bis-cyclometalated iridium(III) complex (tfmppy) 2 Ir(pic) recently synthesized with tfmppy = 5-trifuoromethyl- 2-phenylpyridine and pic = picolinate. The calculations were performed by means of density functional theory (DFT) and time-dependent density functional (TD-DFT) methods using four functionals B3LYP, PBE0, CAM-B3LYP and M06-2X. Calculated geometric parameters agree with the experimental data. CAM-B3LYP and M06-2X lower the HOMO energy level and give a large energy gaps compared with B3LYP and PBE0. The four functionals show that LUMO is delocalized over  ∗ ppy orbital, and HOMO is contributed by  ppy and dIr orbitals. The studied complex gets a remarkably large frst-order NLO response. B3LYP would provide good estimates of the energy gap and shows the strongest values of the frst hyperpo- larizabilities β HRS ; M06-2X and CAM-B3LYP functionals overestimate the gaps and lower β HRS values. PBE0 and B3LYP spectra agree better with the experimental spectrum in the visible region, while CAM-B3LYP and M06-2X are more accurate in UV-C region. Natural transition orbital analysis shows that the weak band observed at 468 nm corresponds to MLCT/ LLCT charge transfer transitions and the intense band observed at 270 nm is mainly assigned to intra-ligand state. Keywords TD-DFT · Picolinate · NTO · Complexes · Absorption spectrum · Iridium · Excited states · Wiberg indices · Optical, nonlinear optical · Hyperpolarizability 1 Introduction In the last years, cyclometalated iridium(III) complexes have attracted much attention and have been extensively studied [1–4] due to their remarkable photoluminescence proper- ties and their wide range of applications, like chemosen- sors, cellular imaging reagents, photocytotoxic agents, and are namely used to produce organic light-emitting diode (OLED) devices [5–9]. Tris-cyclometalated “homoleptic or heteroleptic” iridium complexes based on 2-phenylpyri- dine (ppy) ligands are the most popular cyclometalated iridium(III) complexes due to their high phosphorescence quantum efciency, and they were often studied to improve their performance in OLEDs by introducing different substituents (electron-donating or electron-withdrawing) on ppy ligands at diferent positions on the phenyl or pyridyl fragments in order to adjust their spectroscopic and optical properties to obtain better efciency or to obtain a precise emitting color [10–12]. The structure modifcation can be radical by replacing the phenyl with another group to obtain a bis-cyclometalated “heteroleptic” complex containing two ppy ligands and another bidentate anionic ligand. In this regard, several studies have been carried out on bis-cyclo- metalated iridium complexes containing bidentate auxiliary ligands instead of one ppy ligand such as acetylacetonate and picolinate ligands [13–15]. On the other hand, this type of complexes becomes a good choice in the nonlinear optical feld due to their thermal stability and their greater design fexibility [16] and also due to the diferent form of charge transfer that occur there like metal–ligand charge transfer (MLCT), intramolecular charge transfer (ICT) and ligand–metal charge transfer (LMCT) which plays an important role in increasing the nonlinear optical properties, * Houari Brahim brahim.h@outlook.com 1 Department of Chemistry, University of Saida - Dr Moulay Tahar, 20000 Saida, Algeria