Long-lived emissive intra-ligand triplet excited states (3IL): next generation luminescent oxygen sensing scheme and a case study with red phosphorescent diimine Pt(ii) bis(acetylide) complexes containing ethynylated naphthalimide or pyrene subunits

Abstract

The long-lived room temperature (RT) intra-ligand phosphorescence ((3)IL) of dbbpy Pt(II) bis(acetylide) (dbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine) complexes Pt-1 (λ(em) = 629 nm, τ = 118 μs, quantum yield φ = 17.5%) and Pt-3 (λ(em) = 658 nm, τ = 73.6 μs, φ = 2.1%) (dbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine), containing naphthalimide (NI) and pyrene subunits, respectively, were used for enhanced luminescent oxygen sensing, compared to the model complex dbbpyPt (bisphenylacetylide) (Pt-2, λ(em) = 559 nm, τ = 0.7 μs, φ = 49.6%) with the normal (3)MLCT excited state (metal-to-ligand-charge-transfer). The luminescent lifetimes of Pt-1 and Pt-3 are greatly extended by 168-fold and 105-fold, respectively, when compared to that of Pt-2. The (3)IL features of the photoluminescence of Pt-1 and Pt-3 are supported by DFT/TDDFT calculations, which indicated a NI localized triplet excited state but a normal (3)MLCT/(3)LLCT excited state for Pt-2. The luminescent oxygen sensing properties of the complexes in solution as well as in polymer films were studied. In polymer films, the O(2) sensitivity of Pt-1 (quenching constant K(SV) = 0.085 Torr(-1)) and Pt-3 (K(SV) = 0.062 Torr(-1)) is 70-fold and 50-fold of Pt-2 (K(SV) = 0.0012 Torr(-1)), respectively.

Room‐Temperature Long‐Lived 3IL Excited State of Rhodamine in an NN PtII Bis(acetylide) Complex with Intense Visible‐Light Absorption

“…[28] This is also different from our previous Pt II bis(acetylide) complexes with NI and NDI chromophores. [10,15,29] We therefore propose that the π-conjugated core of Rho-CϵCH is not directly coupled to the Pt II centre. Thus, interaction of the excited states is possible between the Pt II coordination centre and the Rho-CϵCH ligand.…”

“…We have also reported the Pt II bis(acetylide) complex containing NI, which showed a longlived emissive 3 IL state (τ = 118 μs), but very weak absorption in the visible region. [10,29] The dipyrrin moiety has been coordinated to iridium and the emissive 3 IL excited state accessed; however, the T 1 state lifetime was found to be Ͻ15 μs. [44] The BODIPY chromophore has been connected to the bpy ligand of a cyclometalated Ir III complex; in this case the lifetime of the T 1 excited state was 25 μs.…”

“…[10,14,15,29] These complexes, however, suffer from either short absorption wavelengths or short T 1 lifetimes. [15] Considering the large numbers of organic chromophores, much room is left for exploring different organic chromophores to prepare Pt II bis(acetylide) complexes that show intense absorption in the visible region and to access the long-lived 3 IL triplet excited state.…”

“…[30][31][32][33][34][35][36][37][38] To the best of our knowledge, the studies of its triplet excited state and its application as a light-harvesting moiety in transition-metal complexes have never been reported. In our continuous attempts to access the long-lived 3 IL excited state of organic chromophores in transition-metal complexes, [8][9][10][13][14][15]29] we herein report on the incorporation of the rhodamine chromophore into a transition-metal complex to access the rhodamine-localised long-lived 3 IL excited state (Pt-Rho, Scheme 1). Our strategy was to use the aforementioned versatile N ∧ N Pt II bis(acetylide) scaffold to attach the acetylide rhodamine chromophore.…”

Tuning the emission property of carbazole-caped cyclometalated platinum(II) complexes and its application for enhanced luminescent oxygen sensing

“…Fluorescence spectra were recorded on a JASCO FP-6500 or a Sanco 970 CRT spectrofluorometer. Phosphorescence quantum yields were measured with complex Pt( t Bu 2 bpy)(C^CePh) 2 (F ¼ 0.496 in MeCN) as the reference [49]. Luminescence lifetimes were measured on a Horiba Jobin Yvon Fluoro Max-4 (TCSPC) instrument.…”