Synthesis, Structure, and Photophysical Properties of Blue‐Emitting Zinc(II) Complexes with 3‐Aryl‐Substituted 1‐Pyridylimidazo[1,5‐a]pyridine Ligands

Abstract

Six zinc(II) complexes of the general formula [Zn(LR)X2] (1: R = Me, X = Cl; 2: R = Me, X = Br; 3: R = Me, X = I; 4: R = OH, X = Cl; 5: R = OH, X = Br; 6: R = OH, X = I), in which LR is 1‐(pyridin‐2‐yl)‐3‐o‐tolylimidazo[1,5‐a]pyridine (LMe) or 2‐[1‐(pyridin‐2‐yl)imidazo[1,5‐a]pyridin‐3‐yl]phenol (LOH), have been prepared and characterized. The X‐ray structural analysis performed on complexes 1, 3, and 4 showed that both LMe and LOH act as N,N‐bidentate ligands and coordinate to the ZnII metal center through the pyridine ring (Npy) and the pyridine‐like nitrogen atom of the imidazo[1,5‐a]pyridine group (Nim). The photophysical properties of these compounds have been investigated, both in solution and in the solid state. The complexes showed intense blue luminescence when excited with UV light (λexc = 366–410 nm) with λmax of emission between 440–460 nm in the solid state. Complexes 1–3 showed moderate‐to‐good absolute photoluminescence quantum yields (PLQYs) in the solid state with a maximum PLQY of 0.40 for 1. These values were slightly lower than the PLQY of free LMe (0.60). On the other hand, the PLQY of LOH increased after coordination to ZnCl2, and a PLQY of 0.29 was recorded for 4. A possible interpretation of this behavior is reported.

A Quantitative Description of the σ‐Donor and π‐Acceptor Properties of Substituted Phenanthrolines

“…The first step in this method is the optimization of the geometries of the complexes under investigation. In the present study we employed the hybrid functional PBE0, which previously proved to give computational results consistent with the experimental data . Taking into consideration the complex [Mo(CO) 4 (phen)] ( 1 ) as a paradigmatic example of the series 1 – 13 , its molecular structure was optimized starting from the X‐ray data taken from the literature .…”

Diversifying the luminescence of phenanthro-diimine ligands in zinc complexes

“…2), which is in accordance with the reported effect of zinc complexation. [55][56][57][58] The metal perturbation evidently leads to an appreciable π phen → π* py intraligand charge transfer (ILCT) character and stabilization of the π* py orbitals (LUMO) as confirmed by TD-DFT analysis (see the predicted low energy excitations and frontier molecular orbitals of 1X in Table S1 † and Fig. 3, S4 †).…”

“…[58][59][60][61] Halide ligands at the zinc metal show little influence on the emission wavelength of 1Cl and 1I, but drastically affect the intensity of emission that has also been noticed for the related ZnX 2 (X = Cl, I) compounds. 55 Replacing chloride with iodide decreases the quantum yield from 0.45 (1Cl) to 0.02 (1I).…”

Tuning the Fluorescence Emission and HOMO‐LUMO Band Gap in Homoleptic Zinc(II) Complexes with N,O‐Bidentate (Imidazo[1,5‐a]pyrid‐3‐yl)phenols

“…Among nitrogen‐based ligands, imidazo‐pyridines are known for their interesting photochemical properties, both as free molecules and when coordinated to transition metals . In our ongoing study on complexes with nitrogen‐containing ligands, we also investigated zinc(II), and silver(I) complexes bearing N , N ‐coordinated imidazo‐pyridines. Herein, we report on the luminescence properties of a series of homoleptic zinc(II) complexes (Zn(L R ) 2 ) with (imidazo[1,5‐ a ]pyrid‐3‐yl)phenols, which in this case act as N , O ‐bidentate ligands.…”