Bis-Tridentate Ruthenium Complexes with a Redox-Active Amine Substituent: Electrochemical, Spectroscopic, and DFT/TDDFT Studies

Polarity-Induced Morphological Transformation with Tunable Optical Output of Terpyridine-Phenanthro[9,10-d]imidazole-Based Ligand and Its Zn(II) Complexes with I-V Characteristics

Self-assembled nanostructures obtained from various functional π-conjugated organic molecules have been able to draw substantial interest due to their inherent optical properties, which are imperative for developing optoelectronic devices, multiple-color-emitting devices with color-tunable displays, and optical sensors. These π-conjugated molecules have proven their potential employment in various organic electronic applications. Therefore, the stimuli-responsive fabrication of these π-conjugated systems into a well-ordered assembly is extremely crucial to tuning their inherent optical properties for improved performance in organic electronic applications. To this end, herein, we have designed and synthesized a functional π-conjugated molecule (TP) having phenanthro[9,10-d]imidazole with terpyridine substitution at the 2 position and its corresponding metal complexes (TPZn and (TP)2Zn). By varying the polarity of the self-assembly medium, TP, TPZn, and (TP)2Zn are fabricated into well-ordered superstructures with morphological individualities. However, this medium polarity-induced self-assembly can tune the inherent optical properties of TP, TPZn, and (TP)2Zn and generate multiple fluorescence colors. Particularly, this property makes them useful for organic electronic applications, which require adjustable luminescence output. More importantly, in 10% aqueous-THF medium, TPZn exhibited H-type aggregation-induced white light emission and behaved as a single-component white light emitter. The experimentally obtained results of the solvent polarity-induced variation in optical properties as well as self-assembly patterns were further confirmed by theoretical investigation using density functional theory calculations. Furthermore, we investigated the I-V characteristics, both vertical and horizontal, using ITO and glass surfaces coated with TP, TPZn, and (TP)2Zn, respectively, and displayed maximum current density for the TPZn-coated surface with the order of measured current density TPZn > TP > (TP)2Zn. This observed order of current density measurements was also supported by a direct band gap calculation associated with the frontier molecular orbitals using the Tauc plot. Hence, solvent polarity-induced self-assembly behavior with adjustable luminescence output and superior I-V characteristics of TPZn make it an exceptional candidate for organic electronic applications and electronic device fabrication.

Panchromatic Ru(ii)-polypyridyl complexes as NIR emitters

Novel heteroleptic Ru(ii)-polypyridyl complexes were synthesised that exhibit panchromatic absorption up to 750 nm and ³MLCT NIR emission at λ_em > 830 nm.

Substituent Effects on the Electrochemistry and Electronic Coupling of Terphenyl-Bridged Cyclometalated Ruthenium-Amine Conjugated Complexes

Six terphenyl-bridged cyclometalated ruthenium-amine conjugated complexes 4(PF6)-9(PF6) were synthesized and studied. Three different substituents, methoxy, methyl, and chloro, were used to vary the electronic nature of the amine unit, and two terminal ligands 2,2':6',2″-terpyridine (tpy) and trimethyl-4,4',4″-tricarboxylate-2,2':6',2″-terpyridine (Me3tctpy) were used to tune the electronic nature of the ruthenium component. All complexes, except 7(PF6) with the methoxy substituent and Me3tctpy ligand, display two well-separated redox waves in the potential range of +0.5 to +1.1 V versus Ag/AgCl. The regular electrochemical changes of these complexes help to establish the oxidation order of ruthenium and amine and hence of the direction of the electron transfer in odd-electron state. The degree of electronic coupling was estimated by analyzing the donor-to-acceptor charge transfer band in the near-infrared region obtained by oxidative spectroelectrochemical measurements. Electron paramagnetic resonance analyses and density functional theory calculations were performed on the one-electron oxidized forms to obtain information on the spin distribution of these complexes.

Design of Ru(II) Complexes Based on Anthraimidazoledione-Functionalized Terpyridine Ligand for Improvement of Room-Temperature Luminescence Characteristics and Recognition of Selective Anions: Experimental and DFT/TD-DFT Study

In this work we report synthesis and characterization of three rigid and linear rodlike monometallic Ru(II) complexes based on a terpyridine ligand tightly connected to 9,10-anthraquinone electron-acceptor unit through phenyl-imidazole spacer. The motivation of designing these complexes is to enhance their excited-state lifetimes at room temperature. Interestingly it is found that all three complexes exhibit luminescence at room temperature with excited-state lifetimes in the range of 1.6-52.8 ns, depending upon the coligand as well as the solvent. Temperature-dependent luminescence investigations indicate that the energy gap between the emitting ³MLCT state and nonemitting metal-centered state ³MC in the complexes increased enormously compared with parent [Ru(tpy)₂]²⁺. In addition, by taking advantage of the imidazole NH proton(s), which became appreciably acidic upon combined effect of electron accepting anthraquinone moiety as well as metal ion coordination, we also examined anion recognition and sensing behaviors of the complexes in organic, mixed aqueous-organic as well as in solid medium through different optical channels such as absorption, steady-state and time-resolved emission, and ¹H NMR spectroscopic techniques. In conjunction with the experiment, computational investigation was also employed to examine the electronic structures of the complexes and accurate assignment of experimentally observed spectral and redox behaviors.