Effect of β-Ketoiminato Ancillary Ligand Modification on Emissive Properties of New Iridium Complexes

Synthesis, Theoretical Study, and Anticonvulsant Evaluation of N-Arylenaminones

N-Arylenaminones are highly versatile compounds which can be synthesized in relatively simple ways. In this work we explored the synthesis of the four monosubstituted N-(4-R-phenyl)enaminones 3 a (R=NO2), 3 b (R=F), 3 c (R=H), and 3 d (R=OMe) with the goal of determining the influence of the substituents' electronic effects on tautomer stability and biological activity. These compounds were analyzed by means of Density Functional Theory calculations (DFT), to evaluate the relative stability of the possible tautomers. We found that the enaminone structure is the most stable with respect to the ketoimine and iminoenol forms. In addition, all four compounds display anticonvulsant activity, with 3 d being the one that mostly increased latency and mostly decreased the number of convulsions with respect to the control group. The suggested mechanism of action involves blockage of the voltage-dependent Na+ channels, considering that these molecules meet the structural characteristics needed to block the receptor, as is the case of the positive control molecules phenytoin (PHT) and valproic acid (VPA).

Impact of the Anthryl Linking Mode on the Photophysics and Excited-State Dynamics of Re(I) Complexes [ReCl(CO)3(4′-An-terpy-κ2N)]

Rhenium(I) complexes with 2,2′:6′,2″-terpyridines (terpy) substituted with 9-anthryl (1) and 2-anthryl (2) were synthesized, and the impact of the anthryl linking mode on the ground- and excited-state properties of resulting complexes [ReCl(CO)₃(4′-An-terpy-κ²N)] (An—anthryl) was investigated using a combination of steady-state and time-resolved optical techniques accompanied by theoretical calculations. Different attachment positions of anthracene modify the overlap between the molecular orbitals and thus the electronic coupling of the anthracene and {ReCl(CO)₃(terpy-κ²N)} chromophores. Following the femtosecond transient absorption, the lowest triplet excited state of both complexes was found to be localized on the anthracene chromophore. The striking difference between 1 and 2 concerns the triplet-state formation dynamics. A more planar geometry of 2-anthryl-terpy (2), and thus better electronic communication between the anthracene and {ReCl(CO)₃(terpy-κ²N)} chromophores, facilitates the formation of the ³An triplet state. In steady-state photoluminescence spectra, the population ratio of ³MLCT and ³An was found to be dependent not only on the anthryl linking mode but also on solvent polarity and excitation wavelengths. In dimethyl sulfoxide (DMSO), compounds 1 and 2 excited with λ_exc > 410 nm show both ³MLCT and ³An emissions, which are rarely observed. Additionally, the abilities of the designed complexes for ¹O₂ generation and light emission under the external voltage were preliminary examined.

The impact of the anthryl linking mode on the ground- and excited-state properties of [ReCl(CO)₃(4′-An-terpy-κ²N)] with 2,2′:6′,2″-terpyridines (terpy) substituted with 9-anthryl (1) and 2-anthryl (2) was thoroughly investigated. Different attachment positions of anthracene were evidenced to modify the overlap between the molecular orbitals and electronic coupling of the anthracene and {ReCl(CO)₃(terpy-κ²N)} chromophores and thus the optical properties of the resulting complexes. The striking difference between 1 and 2 was demonstrated in the triplet-state formation dynamics.

Efficient OLEDs Based on Slot-Die-Coated Multicomponent Emissive Layer

The optimization of multicomponent emissive layer (EML) deposition by slot-die coating for organic light-emitting diodes (OLEDs) is presented. In the investigated EMLs, the yellow-green iridium complex (Ir) was doped in two types of host: a commonly used mixture of poly(N-vinylcarbazole) (PVK) with oxadiazole derivative (PBD) or PVK with thermally activated delayed fluorescence-assisted dopant (10-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-10H-spiro[acridine-9,9′-fluorene], SpiroAC-TRZ). In this article, OLEDs with EML prepared in air by slot-die coating, facilitating industrial manufacturing, are confronted with those with spin-coated EML in nitrogen. OLEDs based on PVK:PBD + 2 wt.% Ir-dopant exhibit comparable performance: ~13 cd A⁻¹, regardless of the used method. The highest current efficiency (21 cd A⁻¹) is shown by OLEDs based on spin-coated PVK with 25 wt.% SpiroAC-TRZ and 2 wt.% Ir-dopant. It is three times higher than the efficiency of OLEDs with slot-die-coated EML in air. The performance reduction, connected with the adverse oxygen effect on the energy transfer from TADF to emitter molecules, is minimized by the rapid EML annealing in a nitrogen atmosphere. This post-treatment causes more than a doubling of the OLED efficiency, from 7 cd A⁻¹ to over 15 cd A⁻¹. Such an approach may be easily implemented in other printing techniques and result in a yield enhancement.

A facile approach to C-functionalized β-ketoimine compounds via terminal alkylation of a tetralithiated intermediate

A series of C-functionalized β-ketoimine compounds at the terminal methyl groups of the β-ketoimine precursor L^phH₂ (L^ph = C₆H₄[NC(Me)CHC(Me)O]₂) were prepared. This convenient transformation was realized via straightforward double alkylation on the terminal C_α of a novel bis-dianionic β-ketoiminate lithium complex [L^ph'Li₄(THF)₄]₂ (L^ph' = C₆H₄[NC(Me)CHC(O)CH₂]₂) followed by hydrolysis.

Effect of TADF Assistance on Performance Enhancement in Solution Processed Green Phosphorescent OLEDs

Many methods have been proposed to increase the efficiency of organic electroluminescent materials applied as an emissive layer in organic light emitting diodes (OLEDs). Herein, we demonstrate enhancement of electroluminescence efficiency and operational stability solution processed OLEDs by employing thermally activated delayed fluorescence (TADF) molecules as assistant dopants in host-guest systems. The TADF assistant dopant (SpiroAC–TRZ) is used to facilitate efficient energy transfer from host material poly(N–vinylcarbazole) (PVK) to a phosphorescent Ir(III) emitter. We present the analysis of energy transfer and charge trapping—two main processes playing a crucial role in light generation in host–guest structure OLEDs. The investigation of photo-, electro- and thermoluminescence for the double-dopant layer revealed that assistant dopant does not only harvest and transfer the electrically generated excitons to phosphorescent emitter molecules but also creates exciplexes. The triplet states of formed PVK:SpiroAC–TRZ exciplexes are involved in the transport process of charge carriers and promote long–range exciton energy transfer to the emitter, improving the efficiency of electroluminescence in a single emissive layer OLED, resulting in devices with luminance exceeding 18 000 cd/m² with a luminous efficiency of 23 cd/A and external quantum efficiency (EQE) of 7.4%.