Xiuyu Yi

Red-light excitable fluorescent platinum(II) bis(aryleneethynylene) bis(trialkylphosphine) complexes showing long-lived triplet excited states as triplet photosensitizers for triplet–triplet annihilation upconversion

Symmetric and asymmetric platinum(II) bis(phosphine) bis(aryleneethynylene) complexes that show strong absorption of visible light and long-lived triplet excited states with boron dipyrromethane (Bodipy) chromophore visible light-harvesting antennae attached to the Pt(II) centres were prepared for the first time. The bisnuclear complexes Pt-2 and Pt-3, with two Pt(II) coordination centres connected to the π-core of the Bodipy ligands, show red-shifted absorption (e.g.Pt-2, λabs = 643 nm, e = 42 300 M−1 cm−1) compared to the mononuclear Pt(II) complexes (Pt-1 and Pt-4), in which only one Pt(II) coordination centre is connected to the Bodipy chromophore (e.g.Pt-1, λabs = 570 nm, e = 38 300 M−1 cm−1). The complexes are excitable with red-light, which is rare for transition metal complexes. All the complexes show fluorescence at room temperature (627–671 nm, ΦF = 1.4–6.7%), and weak phosphorescence. Long-lived Bodipy ligand-localized triplet excited states are observed for all the complexes (τT = 57.9–72.4 μs) with nanosecond transient absorption spectra, which is supported by spin density analysis. The platinum(II) bis(phosphine) bis(aryleneethynylene) complexes are used as triplet photosensitizers for the first time for red-light excited triplet–triplet annihilation (TTA) based upconversion and upconversion quantum yields of up to 19.0% are observed, and the anti-Stokes shift is up to 0.82 eV. The effects of different triplet energy transfer driving forces on the TTA upconversion with perylene and perylenebisimide as triplet acceptors are investigated. Our results are useful for the preparation of visible light-harvesting linear platinum(II) phosphine alkynyl complexes and for their applications in photocatalysis, non-linear optics and TTA upconversions.

Using C60-bodipy dyads that show strong absorption of visible light and long-lived triplet excited states as organic triplet photosensitizers for triplet–triplet annihilation upconversion

The synthesis of visible light-harvesting C60-bodipy dyads (bodipy = boron-dipyrromethene), and the study of the photophysical properties and the application of dyads as heavy-atom free organic triplet photosensitizers for triplet–triplet annihilation (TTA) based upconversion, are reported. By attaching carbazole units to the π-core of the bodipy chromophore via an ethynyl linker, the absorption wavelength of the antenna in the dyads is readily tuned from 504 nm for the unsubstituted bodipy, to 538 nm (one carbazole unit, e = 61 800 M−1 cm−1) and 597 nm (two carbazole units, e = 58 200 M−1 cm−1). Upon photoexcitation at 538 nm (dyad C-1) or 597 nm (dyad C-2), intramolecular energy transfer from the antenna to the C60 unit occurs, and as a result, the singlet excited state of the C60 unit is populated. Subsequently, with the intrinsic intersystem crossing (ISC) of C60, the triplet excited state of the C60 unit is produced (τT up to 24.5 μs). Thus, without the need for any heavy atoms, the triplet excited state of the dyads was populated upon visible light excitation. The population of the C60-localized triplet excited state of the dyads was confirmed by nanosecond time-resolved transient difference absorption spectra and spin density analysis. The dyads were used as triplet photosensitizers for TTA upconversion and upconversion quantum yields of up to 2.9% were observed.