Unveiling photophysical properties of cyclometalated iridium(iii) complexes with azadipyrromethene and dipyrromethene ancillary: a theoretical perspective

Abstract

A density functional theory/time-depended density functional theory was used to investigate a series of heteroleptic Ir(III) complexes (1-4) employing azadipyrromethene and closely related dipyrromethene derivatives as N^N ancillary ligands, in an effort to explore the underlying reasons of non-radiative behaviour of 1 and further adjust the photophysical properties by the modification of N^N ancillary ligands. The results reveal that the non-emissive phenomenon of 1 can be attributed to the weak 3 ILCT character of the emissive excited state and large structure distortion, as well as the small T opt 1 -S opt 0 energy gap. Upon tailoring the N^N ancillary ligands, the geometry distortion of 2-4 becomes obviously smaller in comparison with 1, accordingly, the spectrum properties are also markedly affected.For instance, the enlargement of frontier molecular orbital energy gaps from 1 to 4 results in the blueshift of their absorption and emission spectra, which is considered to be dominated by the ancillary ligand, while there is a little contribution from the Ir(III) center. Importantly, further analysis on the quantum yield (F PL ) of these complexes also indicates a vital role of N^N ancillary ligands. It is intriguing to note that the designed complex 4 without pendant phenyl rings substituent in the ancillary ligand, possesses an efficient indirect spin-orbital coupling route, larger transition electric dipole moment (m S3 ), higher T opt 1 -S opt 0 energy gap and smaller S 3 -T 1 splitting energy (DE (S3-T1) ), which ensure its higher F PL compared to other complexes. Electronic supplementary information (ESI) available: Tables (S1) Optimized geometrical parameters for 1 in the ground state at different functional levels with experimental data. (S2) Calculated absorption spectra of 1 in CHCl 3 media with different functionals. (S3) Variations of geometry parameters from S 0 to T 1 state for 1-4. (S4) Calculated intramolecular centroid-centroid distances for 1-3. (S5) Molecular orbital compositions (%) of 1-4 in the ground state. (S6) Calculated singlet excited states in detail for 1-4. (S7-S8) The 5d(Ir) orbital compositions (%) in the T 1 state and the electronic transition of S n states based on the T 1 geometries of 2-4. (S9) The net spin values located on Ir(III) of 3 MLCT and 3 MC states for 1-4. (S10) Cartesian coordinates of 1 at the S 0 and T 1 optimized geometry. Fig. (S1) The synthetic routes of the designed ancillary ligands L1-L3. (S2) Optimized structures of 1-4 in the ground state. (S3) Orbital interaction diagram for 1. (S4) Calculated spin-density distributions for the 3 MC states. (S5) Energy level diagram of 3 MLCT/pp* and 3 MC excited states for 1-4 with the normalized S 0 levels. See

Azadipyrromethenes: from traditional dye chemistry to leading edge applications

“…21,35 To date, nine different metals including Cu, Ag, Au, Re, Ir, Rh, Pt, Pd and Zn have been incorporated into heteroleptic metal complexes 40, with a variety of associated ligands and comprehensively characterized (Scheme 17). [36][37][38][39][40][41][42][43][44][45][46] Typically, complexes are formed under mild rt conditions in THF with t-butoxide or DIPEA as base. This points to an ever expanding future for these complexes not just for their own inherent properties but also for catalysis and material applications.…”

“…[36][37][38][39][40][41][42][43][44][45][46] Typically, complexes are formed under mild rt conditions in THF with t-butoxide or DIPEA as base. This points to an ever expanding future for these complexes not just for their own inherent properties but also for catalysis and material applications.…”

Luminescent iridium(iii) dipyrrinato complexes: synthesis, X-ray structures, and DFT and photocytotoxicity studies of glycosylated derivatives

“…24–26 Their structural variations can be used to alter their reactivity from kinetically labile to inert complexes. 27,28 Such complexes revealed pronounced stability in biological media which prompted the exploration of their photoactivity, although most iridium complexes (with phenyl-pyridine and tetrazolate ligand terpyridyl, etc .) explored for ER targeting are cationic and/or neutral complexes.…”

Color-Tuning Strategy for Iridapolycycles [(N∧N)Ir(C∧C)ClPPh3]+ by the Synergistic Modifications on Both the C∧C and N∧N Units

“…A variety of cyclometalating ligands (C ∧ N ligand) and ancillary ligands (N ∧ N or L ∧ X ligand) have been exploited to form Ir­(III) complexes with specific characteristic emission wavelength . Density functional theory (DFT) calculations have recently been used to study these unique complexes with the aim of obtaining a quantitative structure–property relationship elucidation . For example, the highest occupied molecular orbital (HOMO) of a 2-phenylpyridyl Ir­(III) complex mainly localized on metal center and the phenyl rings, whereas the lowest unoccupied molecular orbital (LUMO) primarily distributed on the pyridine rings .…”