Ligand design and nuclearity variation towards dual emissive Pt(ii) complexes for singlet oxygen generation, dual channel bioimaging, and theranostics. Issue 14 (16th March 2022)

• Record Type: Journal Article
• Authors: Shafikov, Marsel Z.; Suleymanova, Alfiya F.; Kutta, Roger J.; Gorski, Alexander; Kowalczyk, Aleksandra; Gapińska, Magdalena; Kowalski, Konrad; Czerwieniec, Rafał
• Is Part Of: Journal of materials chemistry. Volume 10:Issue 14(2022)
• Page Start: 5636
• Page End: 5647
• Publication Date: 2022-03-16
• Subjects: Materials -- Periodicals; Chemistry, Analytic -- Periodicals; Optical materials -- Research -- Periodicals; Electronics -- Materials -- Research -- Periodicals; 543.0284
• DOI: 10.1039/d2tc00257d
• Languages: English
• ISSNs: 2050-7526

Abstract

Abstract : Mono- and dinuclear Pt(ii ) complexes of a new ditopic ligand with a thiophene cyclometalating core are reported. The mononuclear complex shows dual emission of fluorescence and phosphorescence and is demonstrated as a dual channel bioimaging probe. Abstract : Organic ligands comprising thiophene ring(s) afford complexes of transition metals, such as Pt(ii ) and Ir(iii ), with photoluminescence readily tunable via ligand modifications. In this work we demonstrate the targeted design of a N^C-C^N type ditopic ligand with a central thiophene ring as the cyclometalating core and variation of the nuclearity of the complex to fine-tune the photophysical properties of the material. The mononuclear complex Pt-1 shows red T1 → S0 phosphorescence with the emission maximum at λ = 660 nm. The dinuclear complex Pt-2 shows near infrared (NIR) T1 → S0 phosphorescence peaking at λ = 710 nm. In both cases the phosphorescence is quenched by molecular oxygen generating singlet oxygen molecules with high efficiencies of ϕ Δ ≈ 83% (Pt-1 ) and ϕ Δ ≈ 70% (Pt-2, respectively) in air-equilibrated CH2 Cl2 solutions under ambient conditions. The red phosphorescence of Pt-1 is accompanied by green S1 → S0 fluorescence with the maximum at λ = 495 nm. This makes Pt-1 a dual emissive material with two emissions stemming from a single chromophore moiety. Transient absorption studies revealed a relatively low rate of ISC from the S1 state to the triplet manifold with a time constant τ (ISC) of about 4 ps. The slow ISC in Pt-1 is rationalized by a specific electronic structure with a relatively large energy gap Δ E (S1 → T1 ) ≈ 0.63 eV and the higher triplet state T2 being higher in energy than the singlet state S1 . In dinuclear Pt-2, state T2 lies below S1 opening fast T2 → S1 ISC paths with a time constant τ of only ≈ 0.13 ps. The unique dual emission of Pt-1 was beneficial for its imaging in HeLa cells as it enabled switching between green fluorescence and red phosphorescence channels of detection in the time-span of the single confocal luminescence microscopy experiment. Pt-1 represents a prototype of new theranostic agents combining cytotoxic activity with a unique dual wavelength mode of detection.