Search

We describe the mononuclear anionic cyanido-pentafluorophenyl complexes, (NBu4)[Pt(C^N)(C6F5)(CN)] [C^N = 7,8-benzoquinolate (bzq) 1, 2-(2,4-difluorophenyl)pyridinate (dfppy) 2] and the heteropolynuclear derivatives [{Pt(C^N)(C6F5)(CN)}Tl] (C^N = bzq 3, dfppy 4). These complexes were synthesized via a two-step modular synthesis by reaction of the corresponding potassium salts K[Pt(C^N)(C6F5)(CN)], prepared in situ from [Pt(C^N)(C6F5)(DMSO)] and KCN in acetone/H2O, with TlPF6. The structures of {[Pt(bzq)(C6F5)(CN)Tl]·THF}n (3·THF)n and [{Pt(dfppy)(C6F5)(CN)}Tl]4·dioxane [4]4·dioxane, determined by X-ray crystallography, confirm the presence of Pt(II)–Tl(I) bonds [2.9795(6)–3.0736(3) Å], but in the dfppy complex, the incorporation of dioxane, causes a significant structural change. Thus, whereas [3·THF]n achieves a bent-ladder shape extended double chain Tl⋯[Pt⋯Tl]n⋯Pt supported by lateral bridging [Pt](μ-CN)[Tl] ligands, [4]4·dioxane is formed by discrete Pt4Tl4 rectangular aggregates stabilized by [Pt](μ-CN)[Tl] and Pt⋯Tl bonds, which are connected by dioxane bridging molecules through Tl⋯O(dioxane) additional contacts. Solid state emissions are redshifted compared with the mononuclear derivatives 1 and 2 and have been assigned, with the support of theoretical calculations on Pt4Tl4 models, to metal–metal′-to-ligand charge transfer (3MM′LCT [d/s σ*(Pt, Tl) → π*(C^N)]) for 3 and mixed 3MM′LCT/3IL for 4. In fluid THF solution, the complexes are not emissive. At 77 K, 3 and 4 exhibit bright emissions attributed to the formation of bimetallic [{Pt(C^N)(C6F5)(CN)}Tl(THF)x], and anionic [Pt(C^N)(C6F5)(CN)]− fragments. Furthermore, both 3 and 4 exhibit a reversible mechanochromism with a red shift of the emissions upon crushing, suggesting some degree of shortening of metal–metal separation. Finally, complex 3 shows solvatochromic behavior with color/luminescence changes by treatment with a drop of MeOH, CH2Cl2, THF or Et2O, with shifts from 583 in 3-MeOH to 639 nm in 3-THF. However, 4 only demonstrates a bathochromic response to MeOH. [ABSTRACT FROM AUTHOR]

Given the widely recognized bioactivity of 2-arylbenzothiazoles against tumor cells, we have designed a new family of luminescent heteroleptic pentafluorophenyl-bis(2-phenylbenzothiazolyl) PtIV derivatives, fac-[Pt(pbt)2(C6F5)L]n+ (n = 1, 0) [L = 4-Mepy 1, 4-pyridylbenzothiazole (pybt) 2, 4,4′-bipyridine (4,4′-bpy) 3, 1,2-bis-(4-pyridyl)ethylene (bpe) 4 (E/Z ratio: 90/10), 1,4-bis-(pyridyl)butadiyne (bpyb) 5, trifluoroacetate (−OCOCF3) 6] and a dinuclear complex [{Pt(pbt)2(C6F5)}2(μ-bpyb)](PF6)27, in which the trans ligand to the metalated C-(pbt) was varied to modify the optical properties and lipophilicity. Their photophysical properties were systematically studied through experimental and theoretical investigations, which were strongly dependent on the identity of the N-bonded ligand. Thus, complexes 1, 3 and 6 display, in different media, emission from the triplet excited states of primarily intraligand 3ILCT nature localized on the pbt ligand, while the emissions of 2, 5 and 7 were ascribed to a mixture of close 3IL′(N donor)/3ILCT(pbt) excited states, as supported by lifetime measurements and theoretical calculations. Irradiation of the initial E/Z mixture of 4 (15 min) led to a steady state composed of roughly 1 : 1.15 (E : Z) and this complex was not emissive at room temperature due to an enhanced intramolecular E to Z isomerization process of the 1,2-bis-(4-pyridyl)ethylene ligand. Complexes 1–3 and 6 showed excellent quantum yields for the generation of singlet oxygen in aerated MeCN solution with the values of φ(1O2) ranging from 0.66 to 0.86 using phenalenone as a reference. Cationic complexes 1–3 exhibited remarkable efficacy in the nanomolar range against A549 (lung carcinoma) and HeLa (cervix carcinoma) cell lines with notable selectivity relative to the non-tumorigenic BEAS-2B (bronchial epithelium) cells. In the A549 cell line, the neutral complex 6 showed low cytotoxicity (IC50: 29.40 μM) and high photocytotoxicity (IC50: 5.75) when cells were irradiated with blue light for 15 min. These complexes do not show evidence of DNA interaction. [ABSTRACT FROM AUTHOR]

We describe a family of dicationic heteroleptic complexes of the type [Pt(pbt)2(N^N)]Q2, bearing two cyclometalating 2-phenylbenzothiazole (pbt) groups and a N^N phenanthroline-based ligand [N^N = 1,10-phenanthroline (phen) 4, pyrazino[2,3-f][1,10]-phenanthroline (pyraphen) 5, 5-amine-1,10-phenanthroline (NH2-phen) 6], with two different counteranions (Q = CF3CO2 and PF6). Complexes 4–6-PF6 and 4–6-CF3CO2 were obtained through ligand substitution from cis-[Pt(pbt)2Cl2] 2 and cis-[Pt(pbt)2(OCOF3)2] 3, respectively. The molecular structures of 2, 3 and 4-PF6 and the photophysical and electrochemical properties of all complexes were studied in detail. The precursors 2 and 3 exhibit high-energy emissions from 3IL excited states centered on the cyclometalated pbt, with lower efficiency in 2 in relation to 3 by the presence of closer thermally accessible deactivating 3LMCT excited states in 2. The PtIV complexes 4–5-CF3CO2/PF6 display orange emission in CH2Cl2 solution, solid state (298, 77 K) or PS films, arising from a 3IL(pbt) emissive state. The NH2-phen derivatives 6-CF3CO2/PF6 show dual emission associated to two close different emissive states, 3IL′CT (L′ = NH2-phen) and 3IL(pbt), depending on the medium and the excitation wavelength. DFT and time-dependent TD-DFT calculations support these assignments and allow explain the luminescence of these tris-chelate PtIV complexes. [ABSTRACT FROM AUTHOR]

Two series of cyclometalated PtII and IrIII complexes with general formulas [Pt(pbt){PPh2(R)-κP,O}] (2a–2c) and [Ir(pbt)2{PPh2(R)-κP,O}] (3a–3c), where Hpbt is 2-phenylbenzothiazol and PPh2(R) is a diphenylphosphino donor functionalized deprotonated acid (R = o-C6H4CO2a, o-C6H4SO3b, CH2CH2CO2c) are presented. The structures of 1, 2a–2c, 3a and 3b were confirmed by single X-ray diffraction analyses, and the intermolecular interactions in 2a were studied using Hirshfeld surface analysis and non-covalent interaction (NCI) methods on its X-ray structure. Their photophysical properties were investigated by absorption and emission analyses [CH2Cl2, solid (298, 77 K) and doped polystyrene (PS) films], supported by TD-DFT calculations on 1, 2a–2c and 3a. The PtII complexes exhibit bright phosphorescence in the region 525–542 nm, ascribed to a mixed 3IL/3MLCT excited state with a predominant 3IL contribution. The IrIII derivatives (3a–3c) show orange photoluminescence (535–584 nm, 298 K), blue shifted at 77 K (527–560 nm), originated from the admixture of 3IL/3MLCT/3LLCT excited states. Interestingly, the photoluminescence quantum yields of the Pt complexes 2a–2c (φ = 46.5–66.5%) in PS films are remarkably higher than those of the corresponding iridium complexes (φ = 17.3–32%) and the precursor 1 (φ = 17%). The calculated 3MC-3IL/3MLCT energy gap for 2a and 3a accounts for the higher quantum yield of the Pt in relation to the Ir complex. [ABSTRACT FROM AUTHOR]

Given the widely recognized bioactivity of 2-arylbenzothiazoles against tumor cells, we have designed a new family of luminescent heteroleptic pentafluorophenyl-bis(2-phenylbenzothiazolyl) Pt IV derivatives, fac -[Pt(pbt) 2 (C 6 F 5 )L] n + ( n = 1, 0) [L = 4-Mepy 1, 4-pyridylbenzothiazole (pybt) 2, 4,4'-bipyridine (4,4'-bpy) 3, 1,2-bis-(4-pyridyl)ethylene (bpe) 4 ( E / Z ratio: 90/10), 1,4-bis-(pyridyl)butadiyne (bpyb) 5, trifluoroacetate ( - OCOCF 3 ) 6] and a dinuclear complex [{Pt(pbt) 2 (C 6 F 5 )} 2 (μ-bpyb)](PF 6 ) 2 7, in which the trans ligand to the metalated C-(pbt) was varied to modify the optical properties and lipophilicity. Their photophysical properties were systematically studied through experimental and theoretical investigations, which were strongly dependent on the identity of the N-bonded ligand. Thus, complexes 1, 3 and 6 display, in different media, emission from the triplet excited states of primarily intraligand 3 ILCT nature localized on the pbt ligand, while the emissions of 2, 5 and 7 were ascribed to a mixture of close 3 IL'(N donor)/ 3 ILCT(pbt) excited states, as supported by lifetime measurements and theoretical calculations. Irradiation of the initial E / Z mixture of 4 (15 min) led to a steady state composed of roughly 1 : 1.15 ( E  :  Z ) and this complex was not emissive at room temperature due to an enhanced intramolecular E to Z isomerization process of the 1,2-bis-(4-pyridyl)ethylene ligand. Complexes 1-3 and 6 showed excellent quantum yields for the generation of singlet oxygen in aerated MeCN solution with the values of ϕ ( 1 O 2 ) ranging from 0.66 to 0.86 using phenalenone as a reference. Cationic complexes 1-3 exhibited remarkable efficacy in the nanomolar range against A549 (lung carcinoma) and HeLa (cervix carcinoma) cell lines with notable selectivity relative to the non-tumorigenic BEAS-2B (bronchial epithelium) cells. In the A549 cell line, the neutral complex 6 showed low cytotoxicity (IC 50 : 29.40 μM) and high photocytotoxicity (IC 50 : 5.75) when cells were irradiated with blue light for 15 min. These complexes do not show evidence of DNA interaction.

We describe a family of dicationic heteroleptic complexes of the type [Pt(pbt) 2 (N^N)]Q 2 , bearing two cyclometalating 2-phenylbenzothiazole (pbt) groups and a N^N phenanthroline-based ligand [N^N = 1,10-phenanthroline (phen) 4, pyrazino[2,3- f ][1,10]-phenanthroline (pyraphen) 5, 5-amine-1,10-phenanthroline (NH 2 -phen) 6], with two different counteranions (Q = CF 3 CO 2 and PF 6 ). Complexes 4-6-PF6 and 4-6-CF3CO2 were obtained through ligand substitution from cis -[Pt(pbt) 2 Cl 2 ] 2 and cis -[Pt(pbt) 2 (OCOF 3 ) 2 ] 3, respectively. The molecular structures of 2, 3 and 4-PF6 and the photophysical and electrochemical properties of all complexes were studied in detail. The precursors 2 and 3 exhibit high-energy emissions from 3 IL excited states centered on the cyclometalated pbt, with lower efficiency in 2 in relation to 3 by the presence of closer thermally accessible deactivating 3 LMCT excited states in 2. The Pt IV complexes 4-5-CF3CO2/PF6 display orange emission in CH 2 Cl 2 solution, solid state (298, 77 K) or PS films, arising from a 3 IL(pbt) emissive state. The NH 2 -phen derivatives 6-CF3CO2/PF6 show dual emission associated to two close different emissive states, 3 IL'CT (L' = NH 2 -phen) and 3 IL(pbt), depending on the medium and the excitation wavelength. DFT and time-dependent TD-DFT calculations support these assignments and allow explain the luminescence of these tris-chelate Pt IV complexes.

New cyclometalated Pt II complexes with 2-phenylbenzothiazole (pbt) and two different picolinate ligands [Pt(pbt)(R-pic-κ N,O )] (R = H ( 1 ), OH ( 2 )) were prepared. In contrast to 1 , the OH substituent group on 2 allows modulation of the packing in the solid state through donor-acceptor H-bonding interactions with the CH 2 Cl 2 solvent. Thus, three pseudopolymorphs of 2 with different aggregation degrees were isolated, including yellow 2-Y , orange-red 2-R ( 2·0.5CH 2 Cl 2 ) and black 2-B ( 2·0.75CH 2 Cl 2 ) with emissions at 540, 656, and 740 nm, respectively, in the solid state at 298 K. 2-R and 2-B can be transformed to the pristine solid 2 . Studies of their crystal structures show that 1 and 2-Y stack in columns with only π···π stacking interactions, whereas 2-R displays strong aggregated 1D infinite chains based on Pt···Pt and π···π stacking interactions, consistent with the colors and the photophysical properties, measured in several media. Interestingly, 1 and 2 exhibit reversible mechanochromic behavior with high contrast in the color and color emission upon mechanical grinding due to a phase transition between a crystalline and an amorphous state, as confirmed by powder X-ray diffraction (PXRD) studies. Theoretical calculations indicate that Pt···Pt contacts are more relevant in the trimers and tetramers than in the dimers, particularly in their T 1 states, associated with a change from a 3 IL/ 3 MLCT transition in the monomer to 3 MM(L+L')CT in the oligomers. Noncovalent interaction (NCI) theoretical studies indicate that the π···π stacking among chelates also exerts a strong influence in the metal-metal-to-ligand charge transfer transition character.

Two series of cyclometalated Pt II and Ir III complexes with general formulas [Pt(pbt){PPh 2 (R)-κ P , O }] (2a-2c) and [Ir(pbt) 2 {PPh 2 (R)-κ P , O }] (3a-3c), where Hpbt is 2-phenylbenzothiazol and PPh 2 (R) is a diphenylphosphino donor functionalized deprotonated acid (R = o -C 6 H 4 CO 2 a, o -C 6 H 4 SO 3 b, CH 2 CH 2 CO 2 c) are presented. The structures of 1, 2a-2c, 3a and 3b were confirmed by single X-ray diffraction analyses, and the intermolecular interactions in 2a were studied using Hirshfeld surface analysis and non-covalent interaction (NCI) methods on its X-ray structure. Their photophysical properties were investigated by absorption and emission analyses [CH 2 Cl 2 , solid (298, 77 K) and doped polystyrene (PS) films], supported by TD-DFT calculations on 1, 2a-2c and 3a. The Pt II complexes exhibit bright phosphorescence in the region 525-542 nm, ascribed to a mixed 3 IL/ 3 MLCT excited state with a predominant 3 IL contribution. The Ir III derivatives (3a-3c) show orange photoluminescence (535-584 nm, 298 K), blue shifted at 77 K (527-560 nm), originated from the admixture of 3 IL/ 3 MLCT/ 3 LLCT excited states. Interestingly, the photoluminescence quantum yields of the Pt complexes 2a-2c ( ϕ = 46.5-66.5%) in PS films are remarkably higher than those of the corresponding iridium complexes ( ϕ = 17.3-32%) and the precursor 1 ( ϕ = 17%). The calculated 3 MC- 3 IL/ 3 MLCT energy gap for 2a and 3a accounts for the higher quantum yield of the Pt in relation to the Ir complex.