Broadband Visible‐Light‐Harvesting trans‐Bis(alkylphosphine) Platinum(II)‐Alkynyl Complexes with Singlet Energy Transfer between BODIPY and Naphthalene Diimide Ligands

Abstract

A heteroleptic bis(tributylphosphine) platinum(II)-alkynyl complex (Pt-1) showing broadband visible-light absorption was prepared. Two different visible-light-absorbing ligands, that is, ethynylated boron-dipyrromethene (BODIPY) and a functionalized naphthalene diimide (NDI) were used in the molecule. Two reference complexes, Pt-2 and Pt-3, which contain only the NDI or BODIPY ligand, respectively, were also prepared. The coordinated BODIPY ligand shows absorption at 503 nm and fluorescence at 516 nm, whereas the coordinated NDI ligand absorbs at 594 nm; the spectral overlap between the two ligands ensures intramolecular resonance energy transfer in Pt-1, with BODIPY as the singlet energy donor and NDI as the energy acceptor. The complex shows strong absorption in the region 450 nm-640 nm, with molar absorption coefficient up to 88 000 M(-1) cm(-1) . Long-lived triplet excited states lifetimes were observed for Pt-1-Pt-3 (36.9 μs, 28.3 μs, and 818.6 μs, respectively). Singlet and triplet energy transfer processes were studied by the fluorescence/phosphorescence excitation spectra, steady-state and time-resolved UV/Vis absorption and luminescence spectra, as well as nanosecond time-resolved transient difference absorption spectra. A triplet-state equilibrium was observed for Pt-1. The complexes were used as triplet photosensitizers for triplet-triplet annihilation upconversion, with upconversion quantum yields up to 18.4 % being observed for Pt-1.

Photophysical Properties of Visible‐Light‐Harvesting PtII Bis(acetylide) Complexes

“…Bis(phosphine)Pt II bis(acetylide) complex 26 , with Bodipy and NDI moieties, and the reference complexes 27 and 28 were prepared (Figure ) . Complex 26 shows broadband visible‐light‐harvesting ability in the range of 450–650 nm (Figure ).…”

“…Multiple‐chromophore bis(phosphine)Pt II bis(acetylide) complex 26 , together with reference complexes 27 and 28 …”

“…UV/Vis absorption spectra of complexes 26 – 28 . Reprinted from the literature, with permission . Copyright 2014, Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim.…”

“…In deaerated toluene, λ ex = 503 nm for complex 26 , λ ex = 590 nm for complex 27 , and λ ex = 495 nm for complex 28 . Reprinted from the literature, with permission . Copyright 2014, Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim.…”

Harnessing Reversible Electronic Energy Transfer: From Molecular Dyads to Molecular Machines

“…Te mperature-dependent transienta bsorption spectroscopy permitted energy gap determination( 1740 cm À1 )b etween the MMLCT and PNI triplet states alongw ith the time constants associated with the interconversion betweene xcited states, which decayed to the ground state with at ime constant of 65 ms. Zhao and Zhang reported another example where at riplet equilibrium was proposed between aP ta nd ar ylene dye. [36] Ar ange of spirobifluorene bridged heteroleptic mono-and trinuclearc omplexes comprising Pt II ,O s II and Ir III metalsw ere described (26)(27)(28). [37] Here, the luminescence of the tetrad consisting of spirobifluorene-bridgedP t, Ir and Os complexes were studied by comparison with the reference complexes bearing two identical luminophores (Ir or Os) at the periphery.T he LC and 3 M Pt LCT states serve as energy reservoirs for the quasi-isoenergetic metal excited states, resulting in ae xtended excited state lifetimei nt he arrays.…”