Amending the anisotropy barrier and luminescence behavior of heterometallic trinuclear linear M-II-Ln(III)-M-II (Ln(III)=Gd, Tb, Dy; M-II=Mg/Zn) complexes by change from divalent paramagnetic to diamagnetic metal ions

The sequential reaction of a multisite coordinating compartmental ligand LH4 [2-(2-hydroxy-3-(hydroxymethyl)-5-methylbenzylideneamino)-2-methylpropane-1,3-diol] with appropriate lanthanide salts followed by the addition of Mg(NO3)2·6H2O or Zn(NO3)2·6H2O in a 4:1:2 stoichiometric ratio in the presence of triethylamine affords a series of isostructural heterometallic trinuclear complexes containing [Mg2Ln]3+ [Ln = Dy (1), Gd (2) and Tb (3)] and [Zn2Ln]3+ [Ln = Dy (4), Gd (5) and Tb (6)] cores. The formation of 1-6 is demonstrated by X-ray crystallography as well as ESI-MS spectra. All complexes are isostructural possessing a linear trimetallic core with a central lanthanide ion. In this article we have discussed the comprehensive studies, involving synthesis, structure, magnetism and photophysical properties on this family of trinuclear [Mg2Ln]3+ and [Zn2Ln]3+ heterometallic complexes. Complexes 1 and 4 show slow relaxation of the magnetization below 12 K under zero applied direct-current field, but without reaching a neat maximum which is due to the overlapping with a faster quantum tunnelling relaxation mediated through dipole-dipole and hyperfine interactions. Under a small applied direct-current field of 1000 Oe the quantum tunneling was almost suppressed and temperature and frequency dependent peaks were observed, thus confirming the SMM behavior of complexes 1 and 4. The fit of the high-temperature relaxation times to the Arrhenius equation affords an effective energy barrier for the reversal of the magnetization of Ueff =72(2) K with o = 8 x 10-9 s for the SR process and Ueff = 61(2) K with o = 4 x 10-7 s for the FR process for 1 whereas for 4, an effective energy barrier for the reversal of the magnetization Ueff = 67(3) K with o = 4.5 x 10-8 s. To rule out the involvement of intermolecular collaborative interactions in the dynamic of relaxation, we have performed ac susceptibility measurements on 1:10 Dy:Y magnetic diluted samples of of 1 and 4, named as 1' and 4'. Interestingly, the diluted compounds 1' and 4' exhibits SMM behavior under zero magnetic field, thus suggesting that their relaxation processes are single molecular in origin and arise from the M-Dy-M unit. Ab initio CASSCF+RASSI calculations carried out on 1 and 4 confirm that the magnetic anisotropy is axial along the M-Dy-M axis and that the relaxation process occurs through the first excited energy level. Furthermore, the chromophoric [LH3]2- ligand is able to act as an 'antenna' group which was found to be effective in the selective sensitization of the emissions of TbIII-based complexes 3 and 6. The emission quantum yields and the luminescence lifetimes at room temperature are 11.7 % and 0.606 ms for 3, 22.7 % and 0.799 ms for 6

Electrospun fluorescent nanofibers for explosive detection

Development of an instant on-site visual detection method for 2,4,6 trinitrotoluene (TNT) has become a significant requirement of the hour towards a secured society and a greener environment. Despite momentous advances in the respective field, a portable and reliable method for quick and selective detection of TNT still poses a challenge to many reasons attributing to inappropriate usage in subordinate areas and untrained personnel. The recent effort on the fluorescent based detection represents as one of easy method in terms of fast response time and simple on/off detection. Therefore, this chapter provides a consolidation of information relating to recent advances in fluorescence based TNT detection.Further, the main focus will be towards advances in the nanofibers based TNT detection and their reason to improving thesensitivity. © Springer International Publishing Switzerland 2015

Robust Deep-Red Emission in Iridium(III) Complexes Assisted by Ancillary Ligand for Solution-Processable Phosphorescent OLEDs

1

Photophysical and electroluminescence properties of bis(2′,6′-difluoro-2,3′-bipyridinato-N,C4′)iridium(picolinate) complexes: effect of electron-withdrawing and electron-donating group substituents at the 4′ position of the pyridyl moiety of the cyclometalated ligand

Herein, we have synthesized a series of 2′,6′-difluoro-2,3′-bipyridine cyclometalating ligands by substituting electron-withdrawing (–CHO, –CF3, and –CN) and electron-donating (–OMe and –NMe2) groups at the 4′ position of the pyridyl moiety and utilized them for the construction of five new iridium(III) complexes (Ir1–Ir5) in the presence of picolinate as an ancillary ligand. The photophysical properties of the developed iridium(III) compounds were investigated with a view to understand the substituent effects. The strong electron-withdrawing (–CN) group containing the iridium(III) compound (Ir3) exhibits highly efficient genuine green phosphorescence (λmax = 508 nm) at room temperature in solution and in thin film, with an excellent quantum efficiency (ΦPL) of 0.90 and 0.98, respectively. On the other hand, the –CF3 group substituted iridium(III) compound (Ir2) displays a sky-blue emission (λmax = 468 nm) with a promising quantum efficiency (ΦPL = 0.88 and 0.84 in solution and in thin film, respectively). The –CHO substituted iridium(III) complex (Ir1) showed greenish-yellow emission (λmax = 542 nm). Most importantly, the strong electron-donating –NMe2 substituted iridium(III) complex (Ir5) gives a structureless and a broad emission profile in the wavelength region 450 to 700 nm (λmax = 520 nm) with a poor quantum efficiency. An intense blue phosphorescence with impressive quantum efficiency, especially in thin-film noted in the case of the –OMe substituted iridium(III) complex (Ir4). Comprehensive density functional theory (DFT) and time-dependent DFT (TD-DFT) approaches have been performed on the ground and excited states of the synthesized iridium(III) complexes, in order to obtain information about the absorption and emission processes and to gain deeper insights into the photophysical properties. The combinations of a smaller ΔES1–T1 and higher contribution of 3MLCT in the emission process result in the higher quantum yields and lifetime values for complexes Ir1–Ir3. Multi-layered Phosphorescent Organic Light Emitting Diodes (PhOLEDs) were designed using the phosphorescent dopants Ir2, Ir3 and Ir4 and their elecroluminescence properties were evaluated. Compound Ir4 at a doping level of 5 wt% shows the best performance with an external quantum efficiency of 4.7%, in the nonoptimized device, and a power efficiency of 5.8 lm W-1, together with a true-blue chromacity CIEx,y = 0.15, 0.17 recorded at the maximum brightness of 33 180 cd m-2

A Highly Selective Chemosensor for Cyanide Derived from a Formyl-Functionalized Phosphorescent Iridium(III) Complex

A new phosphorescent iridium­(III) complex, bis­[2′,6′-difluorophenyl-4-formylpyridinato-<i>N</i>,<i>C</i>4′]­iridium­(III) (picolinate) (<b>IrC</b>), was synthesized, fully characterized by various spectroscopic techniques, and utilized for the detection of CN^– on the basis of the widely known hypothesis of the formation of cyanohydrins. The solid-state structure of the developed <b>IrC</b> was authenticated by single-crystal X-ray diffraction. Notably, the iridium­(III) complex exhibits intense red phosphorescence in the solid state at 298 K (Φ_PL = 0.16) and faint emission in acetonitrile solution (Φ_PL = 0.02). The cyanide anion binding properties with <b>IrC</b> in pure and aqueous acetonitrile solutions were systematically investigated using two different channels: i.e., by means of UV–vis absorption and photoluminescence. The addition of 2.0 equiv of cyanide to a solution of the iridium­(III) complex in acetonitrile (<i>c</i> = 20 μM) visibly changes the color from orange to yellow. On the other hand, the PL intensity of <b>IrC</b> at 480 nm was dramatically enhanced ∼5.36 × 10²-fold within 100 s along with a strong signature of a blue shift of the emission by ∼155 nm with a detection limit of 2.16 × 10^–8 M. The cyanohydrin formation mechanism is further supported by results of a ¹H NMR titration of <b>IrC</b> with CN^–. As an integral part of this work, phosphorescent test strips have been constructed by impregnating Whatman filter paper with <b>IrC</b> for the trace detection of CN^– in the contact mode, exhibiting a detection limit at the nanogram level (∼265 ng/mL). Finally, density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were performed to understand the electronic structure and the corresponding transitions involved in the designed phosphorescent iridium­(III) complex probe and its cyanide adduct

A Highly Selective Chemosensor for Cyanide Derived from a Formyl-Functionalized Phosphorescent Iridium(III) Complex

A new phosphorescent iridium­(III) complex, bis­[2′,6′-difluorophenyl-4-formylpyridinato-<i>N</i>,<i>C</i>4′]­iridium­(III) (picolinate) (<b>IrC</b>), was synthesized, fully characterized by various spectroscopic techniques, and utilized for the detection of CN^– on the basis of the widely known hypothesis of the formation of cyanohydrins. The solid-state structure of the developed <b>IrC</b> was authenticated by single-crystal X-ray diffraction. Notably, the iridium­(III) complex exhibits intense red phosphorescence in the solid state at 298 K (Φ_PL = 0.16) and faint emission in acetonitrile solution (Φ_PL = 0.02). The cyanide anion binding properties with <b>IrC</b> in pure and aqueous acetonitrile solutions were systematically investigated using two different channels: i.e., by means of UV–vis absorption and photoluminescence. The addition of 2.0 equiv of cyanide to a solution of the iridium­(III) complex in acetonitrile (<i>c</i> = 20 μM) visibly changes the color from orange to yellow. On the other hand, the PL intensity of <b>IrC</b> at 480 nm was dramatically enhanced ∼5.36 × 10²-fold within 100 s along with a strong signature of a blue shift of the emission by ∼155 nm with a detection limit of 2.16 × 10^–8 M. The cyanohydrin formation mechanism is further supported by results of a ¹H NMR titration of <b>IrC</b> with CN^–. As an integral part of this work, phosphorescent test strips have been constructed by impregnating Whatman filter paper with <b>IrC</b> for the trace detection of CN^– in the contact mode, exhibiting a detection limit at the nanogram level (∼265 ng/mL). Finally, density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were performed to understand the electronic structure and the corresponding transitions involved in the designed phosphorescent iridium­(III) complex probe and its cyanide adduct

A Highly Selective Chemosensor for Cyanide Derived from a Formyl-Functionalized Phosphorescent Iridium(III) Complex

A new phosphorescent iridium­(III) complex, bis­[2′,6′-difluorophenyl-4-formylpyridinato-<i>N</i>,<i>C</i>4′]­iridium­(III) (picolinate) (<b>IrC</b>), was synthesized, fully characterized by various spectroscopic techniques, and utilized for the detection of CN^– on the basis of the widely known hypothesis of the formation of cyanohydrins. The solid-state structure of the developed <b>IrC</b> was authenticated by single-crystal X-ray diffraction. Notably, the iridium­(III) complex exhibits intense red phosphorescence in the solid state at 298 K (Φ_PL = 0.16) and faint emission in acetonitrile solution (Φ_PL = 0.02). The cyanide anion binding properties with <b>IrC</b> in pure and aqueous acetonitrile solutions were systematically investigated using two different channels: i.e., by means of UV–vis absorption and photoluminescence. The addition of 2.0 equiv of cyanide to a solution of the iridium­(III) complex in acetonitrile (<i>c</i> = 20 μM) visibly changes the color from orange to yellow. On the other hand, the PL intensity of <b>IrC</b> at 480 nm was dramatically enhanced ∼5.36 × 10²-fold within 100 s along with a strong signature of a blue shift of the emission by ∼155 nm with a detection limit of 2.16 × 10^–8 M. The cyanohydrin formation mechanism is further supported by results of a ¹H NMR titration of <b>IrC</b> with CN^–. As an integral part of this work, phosphorescent test strips have been constructed by impregnating Whatman filter paper with <b>IrC</b> for the trace detection of CN^– in the contact mode, exhibiting a detection limit at the nanogram level (∼265 ng/mL). Finally, density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were performed to understand the electronic structure and the corresponding transitions involved in the designed phosphorescent iridium­(III) complex probe and its cyanide adduct

Dimorphs of a Benzothiophene-quinoline Derivative with Distinct Mechanical, Optical, Photophysical and Conducting Properties

Because of distinct molecular conformations, packing modes, interaction types, and consequently their physicochemical properties, polymorphic forms of organic conjugated small molecules are intrinsically ideal for elucidating the relationship between their microstructures and the transcribed properties. Ethyl-2‐(1‐benzothiophene‐2‐yl)quinoline‐4‐carboxylate (BZQ) exists as dimorphs with distinct crystal habits―blocks (BZB) and needles (BZN). The crystal forms differ in their molecular arrangements―BZB has a slip-stacked column-like structure in contrast to a zig-zag crystal packing with limited π–overlap in BZN―and their photophysical and conducting properties. The BZB crystals characterized by extended π-stacking along [100] demonstrated semiconductor behavior, whereas the BZN, with its zig-zag crystal packing and limited stacking characteristics, was reckoned as an insulator. Monotropically related crystal forms also differ in their nanomechanical properties, with BZB crystals being considerably softer than BZN crystals. This discrepancy in mechanical behavior can be attributed to the distinct molecular arrangements adopted by each crystal form, resulting in unique mechanisms to relieve the strain generated during nanoindentation experiments. Waveguiding experiments on the acicular crystals of BZN revealed the passive waveguiding properties of the crystals. Excitation of these crystals using a 532 nm laser confirmed the propagation of elastically scattered photons (green) and the subsequent generation of inelastically scattered (orange) photons by the crystals. Further, the dimorphs display dissimilar photoluminescence properties; they are both blue-emissive, but BZN displays twice the quantum yield of BZB. This study underscores the integral role of polymorphism in modulating the mechanical, photophysical, and conducting properties of functional molecular materials. Importantly, our findings reveal the existence of light-emitting crystal polymorphs with varying electric conductivity, a relatively scarce phenomenon in the literature

Distinct Mechanoresponsive Luminescence, Thermochromism, Vapochromism, and Chlorine Gas Sensing by a Solid-State Organic Emitter

In this study, we report a synthetically simple donor–acceptor (D–A)-type organic solid-state emitter <b>1</b> that displays unique fluorescence switching under mechanical stimuli. Orange and yellow emissive crystals of <b>1</b> (<b>1O</b>, <b>1Y</b>) exhibit an unusual “back and forth” fluorescence response to mechanical force. Gentle crushing (mild pressure) of the orange or yellow emissive crystal results in hypsochromic shift to cyan emissive fragments (λ_em = 498–501 nm) with a large wavelength shift Δλ_em = −71 to −96 nm, while further grinding results in bathochromic swing to green emissive powder λ_em = 540–550 nm, Δλ_em = +40 to 58 nm. Single-crystal X-ray diffraction study reveals that molecules are packed by weak interactions, such as C–H···π, C–H···N, and C–H···F, which facilitate intermolecular charge transfer in the crystal. With the aid of structural, spectroscopic, and morphological studies, we established the interplay between intermolecular and intramolecular charge-transfer interaction that is responsible for this elusive mechanochromic luminescence. Moreover, we have also demonstrated the application of this organic material for chlorine gas sensing in solid state

Distinct Mechanoresponsive Luminescence, Thermochromism, Vapochromism, and Chlorine Gas Sensing by a Solid-State Organic Emitter

In this study, we report a synthetically simple donor–acceptor (D–A)-type organic solid-state emitter <b>1</b> that displays unique fluorescence switching under mechanical stimuli. Orange and yellow emissive crystals of <b>1</b> (<b>1O</b>, <b>1Y</b>) exhibit an unusual “back and forth” fluorescence response to mechanical force. Gentle crushing (mild pressure) of the orange or yellow emissive crystal results in hypsochromic shift to cyan emissive fragments (λ_em = 498–501 nm) with a large wavelength shift Δλ_em = −71 to −96 nm, while further grinding results in bathochromic swing to green emissive powder λ_em = 540–550 nm, Δλ_em = +40 to 58 nm. Single-crystal X-ray diffraction study reveals that molecules are packed by weak interactions, such as C–H···π, C–H···N, and C–H···F, which facilitate intermolecular charge transfer in the crystal. With the aid of structural, spectroscopic, and morphological studies, we established the interplay between intermolecular and intramolecular charge-transfer interaction that is responsible for this elusive mechanochromic luminescence. Moreover, we have also demonstrated the application of this organic material for chlorine gas sensing in solid state