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We present an in-depth investigation of the influence of chloro-to-iodo exchange on the thermally activated delayed fluorescence (TADF) of a dinuclear platinum(II) complex featuring monodentate halide ancillary ligands. The complexes are constructed using a ditopic bis-N^C^N-chelating ligand of the form (N^C^N–N^C^N)Pt2X2. The initially formed chloro complex (X = Cl) is readily transformed into the iodo analogue (X = I). The change is found to increase the radiative decay rate constant kr by around 3-fold to 3–4 × 105 s−1. This remarkably high value is comparable with the state-of-the-art iridium(III) organometallic phosphors. The improved luminescence properties of the iodo compound are shown to be due to a smaller singlet–triplet energy gap ΔEST compared to the chloro analogue. Iodide reduces the HOMO–LUMO overlap in a multiple resonance-like orbital structure of the complex. Iodination is therefore the first practical strategy shown to improve the TADF properties of diplatinum(II) complexes. The analogous monoplatinum(II) phosphorescent complex is studied in parallel in order to shed light more generally on the effect of iodo ligands on the triplet and singlet states and on spin–orbit coupling (SOC) in platinum(II) complexes.

We present an experimental and theoretical study of aggregate excited states formed by complexes of the type Pt(N^C^N)Cl, which display near-infrared (NIR) photoluminescence in film and NIR electroluminescence in OLED devices. Here, N^C^N represents a tridentate cyclometallating ligand binding through a central benzene ring and two lateral N-heterocycles. A simple theoretical model for the bimolecular excited states of these complexes accounts for the observed behaviour in terms of metal–metal-to-ligand charge-transfer (MMLCT). Detailed photophysical study provides insight into the kinetic properties of Pt–Pt excimers in solution, in films processed from solution, and in vacuum-deposited films. A clear distinction between emission from dimers and higher oligomers (e.g., trimers and tetramers) is evident. We also demonstrate an alternative approach to the architecture of OLEDs based on aggregate states of Pt(II) complexes. An emissive layer (EML) as thin as 1 to 2 nm can be employed, without compromising the efficiency, while reducing the use of the precious-metal compound by >90% compared to typical devices using EMLs of ∼20–40 nm thickness. For example, OLEDs obtained with an EML of 2 nm thickness display an EQE of 1.2% with λEL = 817 nm and a maximum radiosity of 1.46 mW cm−2. As for the photoluminescence of films, the longest-wavelength electroluminescence from devices employing pristine films of emitter is also attributed to trimers and tetramers.

All-round performance: a donor–π–acceptor type push–pull arylene–vinylene conjugated terpyridine showing multifunctional properties of solvatochromism, vapochromism, piezofluorochromism and remarkable fluorescence sensing properties.

A novel dinuclear platinum(ii) complex featuring a ditopic, bis-tetradentate ligand has been prepared. The ligand offers each metal ion a planar O^N^C^N coordination environment, with the two metal ions bound to the nitrogen atoms of a bridging pyrimidine unit. The complex is brightly luminescent in the red region of the spectrum with a photoluminescence quantum yield of 83% in deoxygenated methylcyclohexane solution at ambient temperature, and shows a remarkably short excited state lifetime of 2.1 μs. These properties are the result of an unusually high radiative rate constant of around 4 × 105 s−1, a value which is comparable to that of the very best performing Ir(iii) complexes. This unusual behaviour is the result of efficient thermally activated reverse intersystem crossing, promoted by a small singlet–triplet energy difference of only 69 ± 3 meV. The complex was incorporated into solution-processed OLEDs achieving EQEmax = 7.4%. We believe this to be the first fully evidenced report of a Pt(ii) complex showing thermally activated delayed fluorescence (TADF) at room temperature, and indeed of a Pt(ii)-based delayed fluorescence emitter to be incorporated into an OLED., Efficient thermally activated delayed fluorescence (TADF) in a brightly luminescent diplatinum(ii) complex results in significant enhancement of the radiative decay rate.

UDC 514.7 The object of the present paper is to study three-dimensional trans-Sasakian manifolds admitting η -Ricci soliton. Actually, we study such manifolds whose Ricci tensor satisfy some special conditions like cyclic parallelity, Ricci semisymmetry, ϕ -Ricci semisymmetry, after reviewing the properties of second order parallel tensors on such manifolds. We determine the form of Riemann curvature tensor of trans-Sasakian manifolds of dimension greater than three as Kagan subprojective spaces. We also give some classification results of trans-Sasakian manifolds of dimension greater than three as Kagan subprojective spaces.

In this work we present synthesis and an in-depth photophysical analysis of a di-Pt(II) complex with a ditopic bis-N^C^N ligand. The complex exhibits a dual luminescent behaviour by emitting simultaneously delayed fluorescence and phosphorescence. By comparing with the mono-Pt(II) analogue, we demonstrate that thermally activated delayed fluorescence (TADF) is turned on in the di-Pt(II) complex due to the occurrence of three main factors which are not verified in the mono-Pt(II) analogue: a larger singlet radiative rate (krS), a smaller singlet-triplet energy gap (ΔEST) and a longer phosphorescence decay lifetime (τPH). We observe similar trends among other di-Pt(II) complexes and concluded that bimetallic structures promote conditions favourable for TADF to occur. The diplatinum(II) complex also shows a long wavelength-emissive excimer which yields near infrared electroluminescence, λel = 805 nm, in a solution-processed OLED device with EQEmax = 0.51 %. We believe this is the highest efficiency reported to date for an excimer Pt(II) emitter with λel > 800 nm in a solution-processed OLED device.

In this paper it is shown that a three-dimensional non-cosymplectic quasi-Sasakian manifold admitting Ricci almost soliton is locally $$\phi $$-symmetric. It is proved that a Ricci almost soliton on a three-dimensional quasi-Sasakian manifold reduces to a Ricci soliton. It is also proved that if a three-dimensional non-cosymplectic quasi-Sasakian manifold admits gradient Ricci soliton, then the potential function is invariant in the orthogonal distribution of the Reeb vector field $$\xi$$. We also improve some previous results regarding gradient Ricci soliton on three-dimensional quasi-Sasakian manifolds. An illustrative example is given to support the obtained results.

A BODIPY (borondipyrromethane) based fluorescence probe anchored with N,N-bis(2-(pyridin-2-ylmethoxy)ethyl)aniline receptor (BDPS) has been designed, synthesized and successfully characterized. It can selectively sense Hg2+ ion by giving significant emission enhancement at 514 nm over other biologically and environmentally relevant metal ions in CH3CN/H2O (1:1) medium. The turn-on behaviour of the sensor is due to the metal chelation enhanced fluorescence (MCHEF) effect which has been confirmed by deriving the Job's plot from titration experiment and the high binding constant of 4.19 ± 2.67 × 105 M‐1 between Hg2+ and BDPS. Furthermore, the sensor can efficiently detect Hg2+ in a competitive environment upto submicromolar range revealing high selectivity towards Hg2+. The sensing probe is reversible on adding excess amount of S2− to the solution of BDPS pre-incubated with Hg2+. Reusability of the probe has been demonstrated successfully by multiple cycles of alternative addition of Hg2+ ions followed by S2− ions. Consequently, INHIBIT molecular logic gate can be constructed with the help of OFF-ON-OFF signal on successive addition of Hg2+ (input 1) and S2− (input 2) to the probe. Finally, the test paper experiment demonstrates the practical utility of BDPS for the easy and visual detection of Hg2+.

Highly soluble and emissive poly(metaphenylene-alt-fluorene) π-conjugated alternative copolymers, with pendant terpyridyl binding sites conjugated to metaphenylene unit, have been synthesized through Pd(0)-catalyzed Suzuki coupling polymerization. For solubilizing in common organic solvents, octyl (P1) or 2-(2-(2-methoxyethoxy)ethoxy)ethyl (P2) side groups have been introduced at 9-position of fluorene. The well-defined copolymers have been characterized by multinuclear NMR and tetradetector GPC with excellent PDI values of 1.28 and 1.14 respectively. The blue emissive π-conjugated polymers show remarkable selectivity and sensitivity towards Cu2+ as turn off fluorescent probes without interference by other competing metal ions, as a result of molecular wire effect. The detailed photophysical and sensing studies have been demonstrated to understand the insight of polymer-metal ion interaction which is responsible for selective fluorescence quenching. Moreover, the polymeric sensors (P1 and P2) are reversible, and can also act as secondary sensors for S2−. The limit of detection (LOD) towards Cu2+ in ppb level with relatively high association constants of 4.1–3.2 × 105 M−1 has prompted us to explore as thin-film polymeric sensor for Cu2+ to develop solid state test kits for practical utility.

Fluorenyl-alkynyl based π-conjugated rod-shaped oligomers bearing different central aromatic moieties and functionalizable di-alkynyl termini, such as H––Fl––Fl––Fl––H (OH1), H––Fl––Btz––Fl––H (OH2) and H––Fl––Btd––Fl––H (OH3) where Fl = 9,9-dioctylfluorene, Btz = N-hexylbenzotriazole, and Btd = benzothiadiazole, were successfully synthesized by a Pd(0) catalyzed Stille coupling protocol. Electron withdrawing benzothiadiazole and benzotriazole as strong to moderate acceptors and fluorene as the donor have been incorporated to adjust the Donor–Acceptor (D–A) strength for fine-tuning the bandgap (Eg) as well as the emission wavelength. The corresponding digold(I) σ-complexes (PPh3)Au––Fl––Fl––Fl––Au(PPh3) (OM1), (PPh3)Au––Fl––Btz––Fl––Au(PPh3) (OM2) and (PPh3)Au––Fl––Btd––Fl––Au(PPh3) (OM3) have also been prepared by a reaction of Au(PPh3)Cl and methanolic NaOMe in DCM with the corresponding alkynyl functionalized oligomers to take advantage of the heavy-atom effect on their emissive properties. The synthesized rod-shaped π-conjugated fluorene based oligomers and their binuclear Au(I) σ-complexes have been unambiguously characterized by various spectroscopic tools such as FTIR and multinuclear NMR as well as MALDI-TOF and CHN analyses. The absorption and emission spectral studies exhibited a progressive red shift with increasing the electron withdrawing character of the central aromatic unit. The rod-like oligomers having alkynyl termini and the corresponding digold(I) complexes are found to be blue, cyan and yellow emissive, demonstrating the fine-tuning of the emission wavelength. Most importantly, the fluorene based π-conjugated yellow light emitters OH3 and OM3 are successfully achieved by varying the donor/acceptor moiety to the fluorenyl-alkynyl backbone. The digold(I) diacetylide organometallic wires exhibit phosphorescence at 77 K in degassed CH2Cl2 due to the efficient intersystem crossing from the S1 to the T1 excited state as induced by heavy atoms.

2,6-Diacetylenyl- and 2,6-bis(arylacetylenyl)-functionalized pentamethyl-difluoroborondipyrromethene (BODIPY) derivatives, namely, PBDP1 and PBDP2–4 (aryl = phenyl, 4-methoxyphenyl, or 4-cyanophenyl), respectively, which exhibit extended π-conjugation, were synthesized and characterized by various spectroscopic methods. Significant bathochromic shifts in both absorption and emission were observed upon modifying the structure of the BODIPY core via the strategy of extending its π-conjugation. The derivatives displayed efficient emission in the yellow-to-red spectral region, with a high fluorescence quantum yield and a relatively large Stokes shift. Under conditions of transverse pumping in a cuvette, PBDP1 and PBDP2 exhibited highly efficient and stable laser activity for up to 180 and 110 minutes of continuous irradiation, respectively. Amplified spontaneous emission (FWHM of ca. 2.5 nm) with an efficiency of 41% and 36% was achieved for PBDP1 and PBDP2, respectively, in toluene, which had tunable ranges of 561 to 580 nm and 602 to 617 nm, respectively, on irradiation with a Q-switched Nd:YAG laser at 532 nm. The lasing properties of PBDP3 and PBDP4, which contain electron-donating (–OMe) and electron-withdrawing (–CN) arylacetylenyl moieties, respectively, were also investigated. A corresponding digold(I) diacetylide organometallic complex, namely, (PPh3)Au–CC–BODIPY–CC–Au(PPh3) (PBDP5) was also synthesized and characterized to study the effect of Au(I). PBDP5 exhibited phosphorescence in the vis-NIR region centered at 751 nm at 77 K owing to heavy-atom-induced intersystem crossing.

A series of highly emissive arylene–vinylene conjugated 4′-(4-{2-[aryl]-ethenyl}phenyl)-2,2′:6′,2′′-terpyridines (aryl = 4-methylphenyl, 4-fluorophenyl, 1-naphthyl, and 9-anthralyl in P1–P4 respectively) have been explored for the detection of nitroaromatic compounds (NACs). The synthesized push–pull fluorescent probes show remarkable sensitivity toward NACs in solution, vapor and contact mode as ‘turn-off’ sensors which can be visualized by the naked eye. The photophysical studies reveal that electron transfer occurs from the electron rich arylene–vinylene conjugated terpyridines to the electron-deficient NACs through supramolecular complexation which is further illustrated by the time-resolved fluorescence and 1H NMR titration experiment. The arylene–vinylene conjugated terpyridines offer excellent sensitivity toward picric acid (PA) exhibiting nanomolar detection in contact mode, and ppm level detection in the solution state with association constants in the range of 2.54–8.08 × 104 M−1. The HOMO–LUMO energy levels have been calculated from the electrochemical and TDDFT studies to understand the efficacy and the mechanism of electron transfer from the probe to the NACs leading to fluorescence quenching. The reversibility, recyclability and contact mode detection of PA at a nanomolar level demonstrates the practical utility of the probes as a solid state kit for the onsite detection of NAC explosives.

A blue light emitting phenylene–vinylene functionalized terpyridine conjugate was developed as a ‘turn-on’ fluorescent probe exhibiting a high selectivity towards toxic Cd2+ without interference by other competing metal ions in submicromolar level. The specific response towards Cd2+ and the ability in discriminating Zn2+ offer an opportunity to develop on-site test paper kit for practical utility to detect toxic Cd2+.

A series of heterobimetallic wire-like organometallic complexes [(tpy-C6H4-R)(PPh3)2Ru–C≡C–Fc]+ (tpy-C6H4-R = 4′-(aryl)-2,2′:6′,2′′-terpyridyl, Fc = [(η5-Cp)2Fe], R = -H, -Me, -F, -NMe2 in complexes 5–8, respectively) featuring ferrocenyl and 4′-(aryl)-2,2′:6′,2′′-terpyridyl ruthenium(II) complexes as redox active metal termini, have been synthesized. Various spectroscopic tools, such as multinuclear NMR, IR spectra, HRMS, CHN analyses, and single crystal X-ray crystallography have been utilized to characterize the heterobimetallic complexes. The electrochemical and UV–vis–NIR spectroscopic studies have been investigated to evaluate the electronic delocalization across the molecular backbones of the Ru(II)–Fe(II) heterobinuclear organometallic dyads. Electrochemical studies reveal two well-separated reversible redox waves as a result of successive oxidation of the ferrocenyl and Ru(II) redox centers. The spin density distribution analyses reveal that the initial oxidation process is associated with the Fe...

Organometallic molecular wires with π-conjugation along their molecular backbones are of considerable interest for application in molecular-scale electronics. In this regard, thienylethynyl-based π-conjugated oligomers of three, five and seven thienylethynyl units with -C[triple bond, length as m-dash]C-H termini have been successfully synthesized through stepwise Pd(0)/Cu(i)-catalyzed Sonogashira coupling. The corresponding highly soluble diruthenium(ii) diacetylide complexes (O1-Ru2, O3-Ru2, O5-Ru2 and O7-Ru2, respectively) have been prepared by the reaction of cis-Ru(dppe)2Cl2 and NaPF6 in DCM with the corresponding rigid rod-like thienylethynyl oligomers with one, three, five and seven thienylethynyl π-conjugated segments containing alkynyl termini (O1, O3, O5 and O7). These Ru(ii)-Cl capped diacetylide complexes have been further functionalized by incorporating a phenylacetynyl moiety to afford [Ru(ii)-C[triple bond, length as m-dash]C-Ph]-capped diacetylide organometallic wires (O1-Ru2-Ph, O3-Ru2-Ph, O5-Ru2-Ph and O7-Ru2-Ph). The photophysical properties of the highly soluble thienylethynyl-based oligomers and Ru(ii)-organometallic wires have been explored to understand their electronic properties. Electrochemical studies of the binuclear ruthenium(ii)-alkynyl complexes showed highly interesting results, revealing long-range electrochemical communication between the two remote Ru(ii) termini connected even with five and seven thienylethynyl units. DFT computational studies further support the long range electrochemical communication between the redox active metal termini through heavy participation of the thienylethynyl bridge in the corresponding mono-oxidized mixed valence species of the organometallic wire-like complexes.

High purity Sn(0) has been obtained as a result of reduction of SnO by sodium stannite (Na2SnO2) in aqueous solution. The process stands unique for the production of tin metal. The as-synthesized tin finds applications in synthetic organic chemistry as a reagent for the allylation of aldehydes and ketones in distilled water at room temperature to give rise to the corresponding homoallylic alcohols with high yield. The reaction occurs without the assistance of heat, ultrasonic vibration, co-solvents/co-reagents, etc. Enhancement of the reaction rate of allylation was observed in water rather than THF. The manipulation of allylation reaction becomes easy with active tin material.

Homoallylic alcohols (III), (V) are obtained by allylation of the various substituted aldehydes or ketones using high purity Sn(0) as catalyst.