Complexes trans-Pt(BODIPY)X(PEt3)2: excitation energy-dependent fluorescence and phosphorescence emissions, oxygen sensing and photocatalysis

Abstract

We report on five new complexes with the general formula trans-Pt(BODIPY)X(PEt₃)₂ (Pt–X), where the platinum(II) ion is σ-bonded to a 4,4-difluoro-4-bora-3a,4a-diaza-s-indacen-8-yl (BODIPY) and an anionic ligand X⁻ (X⁻ = Cl⁻, I⁻, NO₂⁻, NCS⁻, CH₃⁻). All five complexes were characterized by multinuclear NMR, electronic absorption and luminescence spectroscopy and by X-ray diffraction analysis. Four of these complexes show efficient intersystem crossing (ISC) from an excited singlet state to a BODIPY-centred T₁ state and exhibit dual fluorescence and phosphorescence emission from the BODIPY ligand. In Pt–I, the fluorescence is almost completely quenched, whereas the phosphorescence quantum yield reaches a value of 40%. The rate of ISC and the ratio of phosphorescence to fluorescence emissions depend on the excitation wavelength (i.e. on which specific transition is excited). The performance of these complexes as one-component oxygen sensors and their photocatalytic activities were tested by Stern–Volmer quenching experiments and by monitoring the oxidation of 1,5-dihydroxynaphthalene with ¹O₂ generated from the long-lived triplet state of the sensitizer by triplet–triplet annihilation with ³O₂. Exceptionally high ¹O₂ generation quantum yields of up to near unity were obtained.