Search

Several γ-cyclodextrin (CD) derivatives mono- or di-substituted by pyrenes at the primary rim of the CD were demonstrated to aggregate into nano-strips in aqueous solutions, with the pyrene moieties interpenetrating into γ-CD cavities. The hydrophobic complexation-induced aggregation provides a rigid chiral environment for the pyrenes and leads to significant electronic circular dichroism (ECD) and circularly polarized luminescence (CPL) activities, giving unprecedently high g abs and g lum values up to 4.3×10 -2 and 5.3×10 -2 , respectively. The aggregates lead to excimer emission with high quantum yields and show B CPL and B i CPL up to 338. 6 M -1  cm -1 and 169.3 M -1  cm -1 , respectively., (© 2022 Wiley-VCH GmbH.)

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.

A cost-effective LED/photodiode(PD)-based time-domain luminescent lifetime measuring device with rugged electronics and simplified algorithms was assembled and successfully used to characterize oxygen sensing films, by continuously monitoring phosphorescence lifetime changes of phosphorescent platinum octaethylporphyrin (PtOEP) in cardo poly(aryl ether ketone) polymer (IMPEK-C) vs. variation of the oxygen partial pressure in a gas mixture (O(2)/N(2)). The results determined by both phosphorescence lifetime and intensity monitoring were compared and the lifetime mode gave results which are in good agreement with the intensity mode. The lifetime-based linear Stern-Volmer plot indicates that the PtOEP molecules are nearly homogeneously distributed in the sensing film. The phosphorescent lifetime of the PtOEP film changes from 75 micros in neat N(2) to less than 2 micros in neat O(2). The sensing system (by combination of the PtOEP sensing film with the home-assembled lifetime device) gives a high lifetime-based O(2) sensing resolution, e.g. about 2 micros Torr(-1) for low O(2) concentration (below 3.5% O(2), V/V). This feasible lifetime device configuration is affordable to most sensor laboratories and the device may facilitate the study of O(2) sensing material with the continuous lifetime monitoring method.

Several γ‐cyclodextrin (CD) derivatives mono‐ or di‐substituted by pyrenes at the primary rim of the CD were demonstrated to aggregate into nano‐strips in aqueous solutions, with the pyrene moieties interpenetrating into γ‐CD cavities. The hydrophobic complexation‐induced aggregation provides a rigid chiral environment for the pyrenes and leads to significant electronic circular dichroism (ECD) and circularly polarized luminescence (CPL) activities, giving unprecedently high gabs and glum values up to 4.3×10−2 and 5.3×10−2, respectively. The aggregates lead to excimer emission with high quantum yields and show BCPL and BiCPL up to 338. 6 M−1 cm−1 and 169.3 M−1 cm−1, respectively. [ABSTRACT FROM AUTHOR]

The poor excited-state properties of bis-terpyridine Ru(II) complexes have significantly limited the applications of these complexes as sensitizers in photocatalysis and triplet–triplet annihilation upconversion. In the present work, two novel ruthenium bis-terpyridine complexes (Ru-1 and Ru-2) conjugated with visible-light-harvesting bodipy chromophores were synthesized. These complexes showed strong absorption of visible light, the bodipy-localized intraligand triplet state (3IL) was efficiently populated, and the phosphorescence of bodipy at room temperature in both complexes was observed. The luminescence lifetimes of these complexes were significantly prolonged, with that of the heteroleptic complex Ru-2 prolonged to 37.9 μs and that of the homoleptic bis-terpyridine complex Ru-1 unprecedentedly prolonged to 356 μs, which was hundreds of times longer than the current longest emissive state achieved in ruthenium terpyridine complexes. The ultra-long triplet lifetimes and strong visible-light absorbing ability made them new candidates of triplet sensitizers, and were first applied to TTA-UC for terpyridine Ru(II) complexes with a Ru-1/Py system showing a ΦUC of 2.93% in dilute solutions at concentrations as low as 1.0 μM. [ABSTRACT FROM AUTHOR]

Pt(ii) Schiff base complexes containing pyrene subunits were prepared using the chemistry-on-complexapproach. This is the first time that supramolecular photochemical approach has been used to tune the photophysical properties of Schiff base Pt(ii) complexes, such as emission wavelength and lifetimes. The complexes show intense absorption in the visible region (= 13100 M−1cm−1at 534 nm) and red phosphorescence at room temperature. Notably, much longer triplet excited state lifetimes (τ= 21.0 μs) were observed, compared to the model complexes (τ= 4.4 μs). The extension of triplet excited state lifetimes is attributed to the establishment of equilibrium between the metal-to-ligand charge-transfer (3MLCT) state (coordination centre localized) and the intraligand (3IL) state (pyrene localized), or population of the long-lived 3IL triplet excited state. These assignments were fully rationalized by nanosecond time-resolved difference absorption spectra, 77 K emission spectra and density functional theory calculations. The complexes were used as triplet sensitizers for triplet–triplet-energy-tranfer (TTET) processes, i.e.luminescent O2sensing and triplet–triplet annihilation (TTA) based upconversion. The O2sensitivity (Stern–Volmer quenching constant) of the complexes was quantitatively evaluated in polymer films. The results show that the O2sensing sensitivity of the pyrene containing complex (KSV= 0.04623 Torr−1) is 15-fold of the model complex (KSV= 0.00313 Torr−1). Furthermore, significant TTA upconversion (upconversion quantum yield ΦUC= 17.7% and the anti-Stokes shift is 0.77 eV) was observed with pyrene containing complexes being used as triplet sensitizers. Our approach to tune the triplet excited states of Pt(ii) Schiff base complexes will be useful for the design of phosphorescent transition metal complexes and their applications in light-harvesting, photovoltaics, luminescent O2sensing and upconversion, etc. [ABSTRACT FROM AUTHOR]

Abstract: Carbazole-caped cyclometalated platinum(II) complexes aryl-R-ppyPt(acac) (where ppy = 4-phenylpyridine, acac = acetylacetonato, aryl = carbazole and R is linker) were synthesized. The carbazole group is attached to the ppy ligand via α-diketo moiety (Pt-1) and (Pt-2) or C−C single bond (Pt-3), by Sonogashira or Negishi coupling reactions. We found that the ethynylene bonds of the C^N ligands were oxidized to α-diketo or methylene-keto structure during the metalation with K2PtCl4. Emissions beyond 550 nm were observed for Pt-1, with electron-withdrawing α-diketo moiety attached to ppy ligand, compared to the emission at 486 nm for the parent complex ppyPt(acac). Extended phosphorescence lifetime (τ P = 12.4 μs) and enhanced phosphorescence quantum yield (Φ P = 66%) were observed for Pt-3 compared to ppyPt(acac) (τ P = 2.4 μs and Φ P = 15%), we attribute the enhanced phosphorescence property to the electron-donating carbazole substituent. With density functional theoretical calculations (DFT), we found that the carbazole moiety is involved in the HOMO (Pt-3), the α-diketo moiety is involved in the LUMO (Pt-1), thus the energy gaps between the HOMO and LUMO in both cases were decreased and red-shifted emission is expected, compared to ppyPt(acac). The different emission properties of 1,2-dione containing complexes (Pt-1 and Pt-2) and the Pt-3 were rationalized by the spin density surface analysis of the complexes. The luminescent O2 sensing properties of these complexes were studied in solution and in polymer films, for which fast response time (3.3 s) and recovery time (3.7 s) were observed. Two-site model fitting indicated that complex Pt-3 is the most sensitive O2 sensing material among the complexes studied herein, with quenching constant of K SV = 0.0238 Torr−1. [Copyright &y& Elsevier]

Abstract: 5,10,15,20-tetraarylporphyrins TPP, TNP and TPyP (where TPP = 5,10,15,20-tetraphenylporphyrin, TNP = 5,10,15,20-tetranaphthalporphyrin and TPyP = 5,10,15,20-tetrapyrenyl-porphyrin) and the corresponding Pt(II) complexes were prepared. The photophysical properties of the porphyrin ligands and the Pt(II) complexes were studied using UV–vis absorption and photo-luminescence spectra; the geometry and electronic structure of the ligands and the complexes were studied via DFT/TDDFT calculations. UV–vis absorption and luminescence emission spectra showed that the added aryl groups did not contribute to the π-conjugation system of either the metal-free porphyrins or the Pt(II) complexes and, therefore, all ligands (and complexes) displayed similar photophysical properties. DFT/TDDFT calculations supported the proposed photophysical process and indicated very weak involvement of the aryl appendents in the low-lying electronic excited states. The luminescent oxygen sensing properties of the Pt(II) complexes were studied in solution as well as in polymer films (monitored via emission intensity and lifetime mode). The results demonstrated that in the case of both the pyrenyl and naphthyl groups, the oxygen sensing character of the complexes could be improved (quenching constant K SV = 0.068 Torr−1 for Pt–TNP vs. K SV = 0.040 Torr−1 for the parent complex Pt–TPP). [ABSTRACT FROM AUTHOR]

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 =1.8μs for complex 1) when compared to the reference complex 3 (i.e. Ru(Phen)(bpy)2, τ =0.8μs). Based on DFT/TDDFT calculations, we propose that 3LLCT/3MLCT 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 N2 and I 100 is the emission intensity under O2 atmosphere). O2 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 7.5s, respectively), which is ideal for practical O2 sensors. Modified Stern–Volmer equation and the two-sites model were used to fit the luminescent O2 sensing data. We found that with tuning the luminescence lifetimes, the luminescence O2 sensitivity of the Ru complexes (quenching constant, k SV) can be improved by up to 20-fold. [ABSTRACT FROM AUTHOR]