Luminescent Alkynylplatinum(II) Complexes of 2,6‐Bis(N‐alkylbenzimidazol‐2′‐yl)pyridine‐Type Ligands with Ready Tunability of the Nature of the Emissive States by Solvent and Electronic Property Modulation

Abstract

A new class of luminescent alkynylplatinum(II) complexes of tridentate bis(N-alkylbenzimidazol-2'-yl)pyridines (bzimpy), [Pt(R,R'-bzimpy)(C[triple chemical bond]C-R'')]X (X=PF(6), OTf), and one of their chloro precursor complexes, [Pt(R,R'-bzimpy)Cl]PF(6), have been synthesized and characterized; one of the alkynyl complexes has also been structurally characterized by X-ray crystallography. Electrochemical studies showed that the oxidation wave is alkynyl ligand-based in nature with some mixing of the metal center-based contribution, whereas the two quasi-reversible reduction couples are mainly bzimpy-based reductions. The electronic absorption and luminescence properties of the complexes have also been investigated. In solution, the high-energy and intense absorption bands are assigned as the pi-pi* intraligand (IL) transitions of the bzimpy and alkynyl ligands, whereas the low-energy and moderately intense absorptions are assigned to an admixture of metal-to-ligand charge-transfer (MLCT) (dpi(Pt)-->pi*(R,R'-bzimpy)) and ligand-to-ligand charge-transfer (LLCT) (pi(C[triple chemical bond]C-R'')-->pi*(R,R'-bzimpy)) transitions. Upon variation of the electronic effects of the arylalkynyl ligands, vibronic-structured or structureless emission bands, originating from triplet metal-perturbed intraligand (IL) or an admixture of triplet metal-to-ligand charge-transfer (MLCT) and ligand-to-ligand charge-transfer (LLCT) excited states respectively, were observed in solution. Interestingly, two of the complexes showed a dual luminescence that was sensitive to the polarity of the solvents. Upon cooling from 298 K to 155 K, drastic color, UV/Vis, and luminescence changes were observed in a butyronitrile solution of 1, and were ascribed to the formation of aggregate species through PtPt and pi-pi stacking interactions. DFT and time-dependent DFT (TD-DFT) calculations have been performed to verify and elucidate the results of the electrochemical and photophysical properties.

Luminescent Platinum(II) Complexes of 1,3‐Bis(N‐alkylbenzimidazol‐ 2′‐yl)benzene‐Type Ligands with Potential Applications in Efficient Organic Light‐Emitting Diodes

“…[9] This difference has been attributed to a stronger trans influence exerted by the anionic phenyl ring on the bzimb ligand compared to the pyridyl unit on the bzimpy ligand. The PtÀCA C H T U N G T R E N N U N G (alkynyl) bond length (2.031 ) in complex 7 is longer than that in the related platinum(II) À bzimpy system.…”

“…[9] This result may be attributed to the presence of an anionic phenyl ring on the bzimb ligand, which substantially raises the energy of the d À d excited state, thereby decreasing the rate of nonradiative deac-tivation pathways. Luminescence spectroscopy: All of these complexes, except complex 8, exhibit strong green luminescence in solution, 77 K glass, and in the solid state.…”

“…[9] All solvents were purified and distilled by using standard procedures before use. 9-(4-Ethynylphenyl)carba- were synthesized according to literature procedures.…”

Cholesterol‐/Estradiol‐Appended Alkynylplatinum(II) Complexes as Supramolecular Gelators: Synthesis, Characterization, Photophysical and Gelation Studies

“…Complex 2 is luminescent only in the glass state and both complexes 3 and 4 with much longer N-alkyl a) The electronic absorption spectra and b) CD spectra of complexes 1 (6.6 10 À5 mol dm À3 ), 5 (3.5 10 À5 mol dm À3 ), and 6 (6.4 10 À5 mol dm À3 ) in dichloromethane at room temperature. With reference to previous spectroscopic studies on other related alkynylplatinum(II) complexes, [12,16] an emission origin of a 3 MLCT [dp(Pt)!p*(2,6-bis(1-alkylpyrazol-3-yl)pyridine)] excited state, with some mixing of 3 LLCT [p(C C)p*! Complex 1 is found to exhibit luminescence at about 541 nm in dichloromethane at 298 K ( Figure 4 and Table 1).…”

Structure‐Based Design of Platinum(II) Complexes as c‐myc Oncogene Down‐Regulators and Luminescent Probes for G‐Quadruplex DNA

“…The amine side-chains were introduced to bzimpy and dPzPy to afford the ligands 2,6-bis ). With reference to previous studies, [35] the absorption bands at l = 385-412 nm are assigned to metal-to-ligand charge transfer (MLCT) and ligand-toligand charge transfer (LLCT) transitions. The absorption spectra of complexes 2-4 are similar to that of 1 in the spectral region of l = 280-450 nm, and are solvent sensitive.…”