Showing papers by "Wenting Wu published in 2010"

Tuning the luminescence lifetimes of ruthenium(II) polypyridine complexes and its application in luminescent oxygen sensing

Abstract: Ru(Phen)(bpy)2 (1) and its new derivatives (2–5) with pyrenyl or ethynylated pyrene and phenyl units appended to the 3-position of the phenanthroline (Phen) ligand were prepared and these complexes generate long-lived room temperature phosphorescence in the red and near IR range (600–800 nm). The photophysical properties of these complexes were investigated by UV-Vis absorption, luminescence emission, transient absorption spectra and DFT/TDDFT calculations. We found the luminescence lifetime (τ)can be drastically extended by ligand modification (increased up to 140-fold), e.g. τ = 58.4 μs for complex 3 (with pyrenyl ethynylene appendents) was found, compared to τ = 0.4 μs for the reference complex 1. Ethynylated phenyl appendents alter the τ also (complex 2, τ = 2.4 μs). With pyrenyl appendents (4 and 5), lifetimes of 2.5 μs and 9.2 μs were observed. We proposed three different mechanisms for the lifetime extension of 2, 3, 4 and 5. For 2, the stabilization of the 3MLCT state by π-conjugation is responsible for the extension of the lifetime. For 3, the emissive state was assigned as an intra-ligand (IL) long-lived 3π–π* state (3IL/3LLCT, intraligand or ligand-to-ligand charge transfer), whereas a C–C single bond linker results in a triplet state equilibrium between 3MLCT state and the pyrene localized 3π–π* triplet state (3IL, e.g.4 and 5). DFT/TDDFT calculations support the assignment of the emissive states. The effects of the lifetime extension on the oxygen sensing properties of these complexes were studied in both solution and polymer films. With tuning the emissive states, and thus extension of the luminescence lifetimes, the luminescent O2 sensing sensitivity of the complexes can be improved by ca. 77-fold in solution (I0/I100 = 1438 for complex 3, vs. I0/I100 = 18.5 for complex 1). In IMPES-C polymer films, the apparent quenching constant KSVapp is improved by 150-fold from 0.0023 Torr−1 (complex 1) to 0.35 Torr−1 (complex 3). The KSVapp value of complex 3 is even higher than that of PtOEP under similar conditions (0.15 Torr−1).

Tuning the emission properties of cyclometalated platinum(II) complexes by intramolecular electron-sink/arylethynylated ligands and its application for enhanced luminescent oxygen sensing

Abstract: We have synthesized five novel cyclometalated Pt(II) complexes (aryl-ppy)Pt(acac) (ppy = 2-phenyl pyridine, aryl = N-butyl naphthalimide (NI) ethynylene for Pt-1, N-butyl naphthalimide (NI)–CH2 –CO– for Pt-2, 4-cyanophenyl – CH2 – CO– for Pt-3, naphthal ethynylene for Pt-4 and naphthal-diketo for Pt-5). For the first time, π-conjugation of the ppy ligands was extended via the CC bond. Deep red/near IR emission (638 nm–700 nm) was observed for the complex containing naphthalimide ethynylene subunit (Pt-1), whereas the close analogue Pt-2 (in which the linker between the NI and the ppy subunit is a –CH2CO– group) shows a relatively blue-shifted emission (540 nm–570 nm) but much longer luminescent lifetime (τ = 25.5 μs) than Pt-1 (τ = 6.6 μs). Simultaneous fluorescence/phosphorescence emissions were observed for Pt-1 and Pt-2, but other complexes show sole phosphorescent emission. The red-shifted phosphorescence of the complexes compared to the model complex ppyPt(acac) (486 nm) was attributed to either the significant electron-sink effect of the NI fragment (Pt-1) (for which the electron withdrawing effect is stronger than the previously reported fluoren-9-one), or the extended π-conjugation of the ppy ligand (via CC bond) (e.g.Pt-4). The substantial tuning of the emission color and the luminescent lifetimes (0.86 μs–25.5 μs) of the complexes were rationalized by theoretical calculations (DFT/TDDFT), i.e. the emissive triplet excited states were assigned as the normal 3MLCT state (give smaller τ values) or the novel ligand-localized 3IL emissive state (give larger τ values). With tuning the luminescent lifetimes, the luminescent O2 sensitivity of the complexes was improved by 117-fold (Stern–Volmer quenching constants KSV = 0.234 Torr−1 for Pt-2vs. KSV = 0.002 Torr−1 for Pt-5).

Effect of the electron donor/acceptor orientation on the fluorescence transduction efficiency of the d-PET effect of carbazole-based fluorescent boronic acid sensors.

Abstract: We have synthesized three new carbazole-based fluorescent boronic acid sensors to investigate the fluorescence transduction efficiency of the novel d-PET effect, in which the fluorophore acts as the electron donor and the protonated amine/boronic acid group as the electron acceptor of the photoinduced electron transfer process (PET). Aryl ethynyl groups are attached at the 3,6-position of carbazole (aryl = 4-dimethylaminophenyl for sensor 1 or phenyl for sensor 2). Sensor 3 is without 3,6-substitutions. The phenylboronic acid moiety is attached at the 9-position (N-atom) of the carbazole in these sensors. We found that 1 and 3 are d-PET sensors (fluorophore as the electron donor, supported by DFT/TDDFT calculations), which show diminished emission at acidic pH but intensified emission at neutral/basic pH, which is in stark contrast to the normal a-PET (fluorophore as the electron acceptor) sensors, e.g., 2, which shows intensified emission at acidic pH but diminished emission at neutral pH. The fluorescen...

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 (3IL) of dbbpy Pt(II) bis(acetylide) (dbbpy = 4,4′-di-tert-butyl-2,2′-bipyridine) complexes Pt-1 (λem = 629 nm, τ = 118 μs, quantum yield ϕ = 17.5%) and Pt-3 (λem = 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, λem = 559 nm, τ = 0.7 μs, ϕ = 49.6%) with the normal 3MLCT 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 3IL 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 3MLCT/3LLCT 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 O2 sensitivity of Pt-1 (quenching constant KSV = 0.085 Torr−1) and Pt-3 (KSV = 0.062 Torr−1) is 70-fold and 50-fold of Pt-2 (KSV = 0.0012 Torr−1), respectively.

Tuning the Emission Colour of Triphenylamine-Capped Cyclometallated Platinum(II) Complexes and Their Application in Luminescent Oxygen Sensing and Organic Light-Emitting Diodes

Abstract: [(aryl-ppy)pt(acac)] (ppy = 2-phenylpyridine, acac = acetylacetonato) derivatives with triphenylamine (tpa) substituents on the ppy ligand have been prepared. the tpa fragment is either directly cyclometallated (pt-1) or attached to the ppy ligand through a c-c single bond (pt-2) or a novel alpha-diketo group (pt-3). all the complexes show room-temperature phosphorescence in fluid solution with emission bands in the range of 530-590 nm, which are red-shifted relative to the model complex [ppypt(acac)] (lambda(em) = 486 nm). this emission colour tuning effect is attributed to either an elevated homo energy caused by electron-donating tpa substituents on the ppy ligand or a decreased lumo energy caused by the electron-trap effect of electron-withdrawing substituents; both result in a smaller homo-lumo energy gap and thus red-shifted emission. the complexes show extended luminescence lifetimes (tau = 3.0-5.5 mu s) relative to the parent complex [ppypt(acac)] (tau = 2.6 mu s). the luminescent oxygen-sensing properties of the complexes were studied in solution and polymer films. white light emission was observed with an oled device fabricated with complex pt-3 with cie coordinates of (0.32, 0.32).

Observation of Room‐Temperature Deep‐Red/Near‐IR Phosphorescence of Pyrene with Cycloplatinated Complexes: An Experimental and Theoretical Study

Abstract: Pyrene-containing cyclometallated Pt" complexes, with the pyrene moiety directly cyclometallated (Pt-1) or connected to a 2-phenylpyridine (ppy) ligand through a C-C (Pt-2) or C=C bond (Pt-3), and a control complex with a phenyl group attached to the ppy ligand (Pt-4) have been prepared. Room-temperature deep-red/near-IR (NIR) phosphorescence emission (650-800 nm) was observed for Pt-1, Pt-2 and Pt-3, whereas Pt-4 showed emission at 528 nm. We found that Pt-2, in which the pyrene moiety is not directly cyclometallated, shows intense pyrene-based phosphorescence, which contrasts with a previous report that direct cyclometallation is necessary for the observation of the phosphorescence of pyrene in cyclometallated complexes. Besides the phosphorescence emission in the deep-red/near-IR range, a fluorescence emission band at higher energy was observed. Thus, these complexes can be described as unichromophore multi-emissive materials. Normal 3 MLCT/ 3 IL emission at 528 nm was observed for Pt-4. The UV/Vis absorption and phosphorescence emissions of the complexes were rationalized by DFT/ TDDFT calculations. Theoretical calculations propose pyrene-localized T 1 states ( 3 IL) for Pt-1, Pt-2 and Pt-3, which is supported by the experimental results. The complexes were used in luminescent O 2 -sensing experiments. These studies will be helpful in the development of room-temperature phosphorescent materials and their application as luminescent molecular sensing or electroluminescent materials are promising.

Enhanced luminescence oxygen sensing property of Ru(II) bispyridine complexes by ligand modification

Abstract: Phenylethynylene containing polypyridyl ruthenium (Ru) complexes 1 and 2 were prepared using chemistry-on-complex approach. The luminescent lifetimes of these complexes were extended by more than 2-fold ( τ = 1.8 μs for complex 1 ) when compared to the reference complex 3 (i.e. Ru(Phen)(bpy) 2 , τ = 0.8 μs). Based on DFT/TDDFT calculations, we propose that 3 LLCT/ 3 MLCT mixed states are the emissive triplet states of 1 and 2 . Luminescence oxygen sensitivity of the complexes are improved with extension of the lifetimes, e.g. I 0 / I 100 = 15.4 for complex 3 , but I 0 / I 100 = 36.8 was observed for the complex 1 in MeCN solution ( I 0 is the emission in N 2 and I 100 is the emission intensity under O 2 atmosphere). O 2 sensitivity of the complexes were also studied in polymers IMPES-C, PES-C and polyvinyl chloride (PVC). The IMPES-C sensing film demonstrated very short response time and recovery time (3.4 and 7.5 s, respectively), which is ideal for practical O 2 sensors. Modified Stern–Volmer equation and the two-sites model were used to fit the luminescent O 2 sensing data. We found that with tuning the luminescence lifetimes, the luminescence O 2 sensitivity of the Ru complexes (quenching constant, k SV ) can be improved by up to 20-fold.

Synthesis of polypyridyl ruthenium complexes with 2-(1-aryl)-1H-imidazo[4,5-f]-1,10-phenanthroline ligand and its application for luminescent oxygen sensing

Abstract: Polypyridyl ruthenium (Ru) complexes 1–3 were prepared. Their photophysical properties were investigated by UV-Vis absorption and luminescence emission spectra. The luminescent lifetimes of these Ruthenium complex were prolonged by more than 5 folds (τ = 2.50 μs for complex 3) when compared with the parent Ru complex 1 (τ = 0.45 μs). We propose that the extended luminescent lifetime of complex 3 is due to the equilibrium between 3MLCT state and the pyrene localized 3π-π* triplet state (3IL). The luminescent O2-sensing property of the complexes in solution and the IMPEK-C polymer film were studied, and the O2 sensing was quantified with the two-site model. The oxygen-sensing property of the Ru complexes can be improved by 104-fold with extension of the luminescent lifetimes. For example, the quenching constant K SV was improved from 0.0023 Torr−1 of 1 to 0.2393 Torr−1 for 3. Our results demonstrated a versatile approach for the preparation of Ru (II) polypyridine complexes with extended luminescent lifetimes as functional materials, for example, for luminescent oxygen-sensing applications.