Red Fluorescence In Solid State Research Articles

Synthesis, Crystal Structure, and Photophysical Properties of Bromothiophene-Functionalized BF2-Curcuminoid as a Versatile Building Block.

A novel bromothiophene-functionalized BF2-curcuminoid (BTC-BF2) is synthesized by Knoevenagel condensation reaction. The structure of BTC-BF2 is determined by 1H-nuclear magnetic resonance (1H NMR), 13C-nuclear magnetic resonance (13C NMR), and high-resolution mass spectrometry (HRMS). Moreover, a nearly coplanar single crystal structure is successfully obtained and form a mesh structure through intermolecular multiple C─H···F hydrogen bond interactions. As expected, as-prepared BTC-BF2 exhibits solvent-dependent photophysical properties in solvents with different polarity and an intense red solid-state fluorescence. Density functional theory calculations further verify the relationships between its intrinsic electronic features and the photophysical properties. For its potential application aspect, BTC-BF2 shows a certain ability to generate singlet oxygen under irradiation with 530nm green light. Moreover, BTC-BF2 can be utilized as versatile building block to construct novel far-red or NIR BF2-curcuminoid complexes for widely biological applications.

Design, synthesis, and biological application of A-D-A-type boranil fluorescent dyes.

For the first time, three acceptor-donor-acceptor (A-D-A)-type boranil fluorescent dyes, CSU-BF-R (R = H, CH3, and OCH3), featuring phenothiazine as the donor, were designed and synthesized. CSU-BF-R exhibited remarkable photophysical characteristics, including large Stokes shifts (>150 nm), high fluorescence quantum yields (up to 40%), long-wavelength emissions, and strong red solid-state fluorescence. Moreover, these CSU-BF-R fluorescent dyes were demonstrated to function as highly selective and sensitive ratiometric fluorescent probes for detecting hypochlorous acid (HClO). The preliminary biological applications of CSU-BF-OCH3 for sensing intracellular HClO in living cells and zebrafish were demonstrated. Therefore, CSU-BF-R possess the potential to further explore the physiological and pathological functions associated with HClO and provide valuable insights into the design of high-performance A-D-A-type fluorescent dyes.

Two-photon AIEgen based on dicyanoisophorone derivative: Synthesis, characterization and cells imaging

A dicyanoisophorone derivative (1) with a D-π-A structure has been synthesized. 1 displayed characteristic of intramolecular charge transfer (ICT) and exhibited very weak fluorescence in solvents (ϕf ≤ 0.01) but strong red fluorescence in solid-state (ϕf = 0.45). Mechanism demonstrated that the strong emission in solid state resulted from aggregation-induced emission (AIE). Furthermore, 1 exhibited a strong two-photon fluorescence in solid-state and a bright two-photon fluorescence imaging in live cells was obtained upon irradiation with 900 nm fs laser.

Orange-red thermally activated delay fluorescence emitters based on asymmetric difluoroboron chelated enaminone: Impact of donor position on luminescent properties

Asymmetric enaminone difluoroboron complexes (BFs) exhibit highly solid emission and appropriated electron-accepting properties, whereas the position of the substituents has a significant influence on their optical properties due to the structural asymmetry. In this work, we employed BF as acceptor and 9,9-dimethylacridine (DMAC) as donor to construct two thermally activated delay fluorescence (TADF) molecules DMAC-BF and BF-DMAC, in which DMAC unit was set on the B-O and B-N sides of BF, respectively. DMAC-BF and BF-DMAC exhibited the broad orange-red emission bands in toluene, while they emitted yellow and red fluorescence in solid state, respectively. The photoluminescence quantum yield (PLQY) of DMAC-BF (52%) is higher than that of BF-DMAC (29%), owing to its lower nonradiative decay rate. Solution-processed organic light-emitting diode (OLED) devices based on both of DMAC-BF and BF-DMAC exhibited orange-red electroluminicence spectra. Owing to its higher photoluminescence quantum yield, DMAC-BF-based OLED exhibited better electroluminicence performance with a maximum current efficiency of 24.9 cd/A, a maximum power efficiency of 23.0 lm/W, and a maximum EQE of 11.3%.

Effect of π-conjugation on solid-state fluorescence in highly planar dyes bearing an intramolecular H-bond

Efficient solid emitters with planar architectures are desirable for some practical applications. However, molecules with coplanar structures and conformational rigidity generally exhibit small Stokes shifts, thus resulting in self-absorption. Multi-aromatic hydrocarbons are one typical example that easily undergoes aggregation-caused quenching (ACQ) due to intermolecular π-π interactions. Herein, a highly planar seven-ringed dye containing benzothiazole- and triphenyl-fused moieties (HTpT) without any bulky or propeller-shaped substituent at its periphery was facilely synthesized from a Cu+-catalyzed Scholl reaction. By extending the phenyl in excited-state intramolecular proton transfer (ESIPT)-active dye (HBT) to naphthyl (HNT) and to triphenyl (HTpT), HNT shows hypsochromic emission and small Stokes shift (20 nm) in comparison with parent HBT, and suffers from ACQ. Contrarily, HTpT exhibits bright red solid-state fluorescence (λem: 600 nm, Φf: 22.7%) with a 200 nm Stokes shift. Steady-state fluorescence spectra, theoretical calculations, and X-ray diffraction analysis are performed to elucidate these different photo-physical properties. In addition, unlike most lysosomal targeting probes containing proton-binding amino or morpholine moieties, which can cause an “alkalinizing effect” that interferes with the activity of normal cells, HTpT without a basic amino group can specifically light up cellular lysosomes.

Chlorine (Cl) - Substituted Carbazole Based A-π-D-π-a Push-Pull Chromophores as Aggregation Enhanced Emission (AEE) Active Viscosity Sensors: Synthesis, DFT and NLO Approach.

Three new carbazole functionalized A-π-D-π-A extended chromophores 4a, 4b and 4c comprising of different chemical functional groups on C=C bond with the assistance of chlorovinylene group in π-conjugation are synthesized and investigated spectroscopically. We have investigated the effect of different electron acceptors - carboxycyanomethylene, dicyanomethylene and 2-(benzothiazol-2-yl) cyanomethylene, the effect of the insertion of chlorine in π-conjugation on photophysical properties and the effect of double acceptors. The chromophores 4a, 4b and 4c exhibited positive solvatochromism with large Stokes shifts and bright orange to red solid-state fluorescence. Amongst all the three compounds 4c exhibited maximum emission wavelength at 615nm in DMSO. They presented characteristic twisted intramolecular charge transfer (TICT) emission. Observations exhibited that 4c containing long hexyl group in donor unit and 2-(benzothiazol-2-yl) cyanomethylene as an acceptor group formed an aggregate in the mixture of solvents and exhibited better aggregation enhanced emission (AEE) compared to the other two derivatives. Amongst the three styryls, 4c showed the highest emission intensity 299a.u. at 90% water:DMF fraction (fw). Chromophores 4a-4c also exhibited good fluorescence response towards viscosity. Among the three fluorescent molecular rotors (FMR), 4c exhibited excellent viscosity sensitivity with x value = 0.687. The Non-linear (NLO) characters are estimated with the help of solvatochromic and computational methods using the functionals, B3LYP and CAM-B3LYP. The dyes showed large "linear polarizability (αCT)", "first order hyperpolarizability" (β) and "second order hyperpolarizability" (γ) values which show that synthesized styryls can be used as a "NLO" material. The αCT, β and γ for 4c are found to be the maximum amongst the all three dyes which can be ascribed to the smaller band gap apparent from experimental as well as DFT method.

Design and construction of lanthanide metal-organic frameworks through mixed-ligand strategy: Sensing property of acetone and Cu2+

Four isostructural 3D lanthanide metal-organic frameworks (Ln-MOFs) {[Ln(L)(ox)0.5(H2O)2]·H2O}n (Ln=Pr 1, Nd 2, Sm 3 and Eu 4) were constructed by 5-hydroxyisophthalic acid (H2L) and oxalate (ox) through solvothermal methods, which show a (4,5)-connected tcs net with the point symbol of (44·62)(44·66). Compound 4 exhibits an intense red fluorescence in solid state and is an excellent dual-functional recyclable luminescent sensor which can sense acetone and Cu2+ with high sensitivity and selectivity simultaneously.

A BODIPY-based dye with red fluorescence in solid state and used as a fluorescent and colorimetric probe for highly selective detection of cyanide

Borondipyrromethene (BODIPY) dyes with strong red solid-state photoluminescence are highly desirable for their applications. In this work, a novel BODIPY dye (1) containing para-bromophenyl at meso position as a molecular separator and dicyanovinyl group on the 2 position as asymmetrical moiety was prepared. The emission peaks of 1 in THF and powder are 548nm and 640nm with emission quantum yield of 55.4% and 4.7%, respectively. Moreover, 1 can be used as a fluorescent and colorimetric probe for the detection of cyanide, which is attributable to the addition of CN− to the electron-deficient dicyanovinyl group of 1. It shows that the color changes from yellow to purple when CN− is added to 1 in THF/H2O (10/1, v/v). The maximum emission intensity at 548nm is quenched 96%, which constitutes the fluorescence signature for cyanide detection. Furthermore, probe 1 achieves rapid detection of cyanide anion within 1min. However, other anions do not induce any significant change of absorption/emission spectrum of 1. Notably, the test strips and silica based – 1 can successfully detect CN−.

Effect of alkoxy side chain length on the solid-state fluorescence behaviour of bisazomethine dyes possessing dipropylamino terminal group

A study was conducted on the optical properties of alkoxy-substituted bisazomethine dyes possessing a dipropylamino terminal group in solution and the solid state. All of the derivatives had similar optical properties in chloroform solution, showing weak fluorescence quantum yield of 5%. In the solid state, the fluorescence behaviour was found to be dependent on the length of the alkoxy side chain. The solid-state fluorescence intensity of the derivatives with the short alkoxy side chains (methoxy, propoxy, and butoxy) was rather low compared to that of the other derivatives in the near-infrared region. However, in the case of the derivatives with the ethoxy side chain the red solid-state fluorescence quantum efficiency improved to 13% at around 700 nm. On the other hand, the derivatives with the middle (pentyloxy to octyloxy) to long (dodecyloxy, hexadecyloxy, and eicosanoxy) alkoxy side chains emitted at around 680 nm, producing enhanced red fluorescence compared to that of the chloroform solution. In particular, the derivative with the hexyloxy side chain showed the highest fluorescence quantum efficiency of over 20% in the solid state. To determine the influence of the alkoxy side chain length on the observed solid-state fluorescence behaviour, X-ray structure analysis was carried out focusing on the molecular arrangement of bisazomethine dyes in crystals. The crystal structures were analysed based on the molecular arrangements of their geometrical characteristics. The result indicated that their solid-state fluorescence depends on the relative positional relationship of the neighbouring molecules and the intermolecular distance resulting from the alkoxy side chain length.

Dipyrrolylquinoxaline difluoroborates with intense red solid-state fluorescence.

A set of organic fluorescent dyes of dipyrrolylquinoxalines (PQs ) and their BF2 complexes (BPQs ) were synthesized from commercial reagents, and were characterized by their X-ray structural analysis, and optical and electrochemical properties. BPQs showed intense broad absorption in the visible region in the solution-state. In comparison with that of PQs , there is an over 110 nm red-shift of the absorption maximum in the BPQs (up to 583 nm). Interestingly, dyes all exhibit red solid-state fluorescence with moderate to high fluorescence quantum yields except for PQ which showed bright yellow solid-state fluorescence. X-ray structures of BPQs showed the planar structure of quinoxaline with one pyrrole unit via the BF2 chelation and the almost perpendicular orientation of the uncoordinated pyrrole to the NBN core plane (the dihedral angle of 70-73°). The extended π-conjugation was in good agreement with the observed red-shift of the spectra. These dyes formed well-ordered intermolecular packing structures via the intermolecular hydrogen bonding between the N atoms of quinoxaline moieties and the NH units of adjacent pyrroles. The lack of π-π stacking in their crystal packing structures may explain the interestingly intense solid-state fluorescence of these dyes.

Structure, absorption and fluorescence of (bi)thiophene substituted methylidene-pyrrolinones

Four thiophene and bithiophene substituted methylidene-pyrrolinones were synthesized and their absorption and fluorescence properties were compared with previously reported behavior of their phenyl and biphenyl substituted analogues. Their structures were estimated theoretically by density functional theory (DFT) and proved by X-ray diffraction in two cases. Thiophene derivatives show a considerable bathochromic shifts in absorption with respect to phenyl analogues, in accordance with theoretical predictions based on time dependent DFT. Conjugation extension caused a bathochromic shift in absorption, too. All compounds show fluorescence in low temperature solvent glass, while only one bithiophene substituted derivative fluoresce weakly in room temperature solution. Three of four N-methylated derivatives show strong yellow, orange and red solid-state fluorescence. An ability of solid-state fluorescence was correlated with nearest neighbor out-of-plane interactions in crystal.

Synthesis, characterization and fluorescence of N,N'-BIS (6-metyl-2-pyridine-carboxylamide-N-oxide)-1,2-ethane and corresponding rare earth (III) complexes

A new ligand, N,N-BIS (6-metyl-2-pyridinecarboxylamide-N-oxide)-1,2-ethane (L) and six lanthanide(III) complexes (RE=La, Sm, Eu, Tb, Gd, Yb) were synthesized and characterized in detail. The results indicated that the composition of the binary complexes was determined as [REL(H 2O)(NO 3) 2]NO 3· nH 2O ( n=0–2), and the Eu 3+ complex had bright red fluorescence in solid state. Three complexes of Eu 3+, Tb 3+, and Gd 3+ with 6-methylpicolinic acid N-oxide (L') were also synthesized. The relative intensity of sensitized luminescence for Eu 3+ increased in the following order: L>L'. The phosphorescence spectra of the Gd 3+ complexes at 77 K were measured. The energies of excited triplet state for the ligands were 20704 cm −1 (L) and 20408 cm −1 (L'). The facts that the ligands sensitized Eu 3+ strongly and the order of the emission intensity for Eu 3+ complexes were explained by Δ E(T- 5D). This meant that the triplet energy level of the ligand was the main factor to influence RE 3+ luminescence.

Synthesis, characterizations and luminescent properties of three novel aryl amide type ligands and their lanthanide complexes

Three new aryl amide type ligands, N-(phenyl)-2-(quinolin-8-yloxy)acetamide (L1), N-(benzyl)-2-(quinolin-8-yloxy)acetamide (L2) and N-(naphthalene-1-yl)-2-(quinolin-8-yloxy)acetamide (L3) were synthesized. With these ligands, three series of lanthanide(III) complexes were prepared: [Ln(L1)2(NO3)2]NO3, [Ln(L2)2(NO3)2(H2O)2]NO3·H2O and [Ln(L3)2(NO3)2(H2O)2]NO3·H2O (Ln=La, Sm, Eu, Gd). The complexes were characterized by the elemental analyses, molar conductivity, 1H NMR spectra, IR spectra and TG–DTA. The fluorescence properties of complexes in the solid state and the triplet state energies of the ligands were studied in detail, respectively. It was found that the Eu(III) complexes have bright red fluorescence in solid state. The energies of excited triplet state for the three ligands are 20325cm−1 (L3), 21053cm−1 (L2) and 22831cm−1 (L1), respectively. All the three ligands sensitize Eu(III) strongly and the order of the emission intensity for the Eu(III) complexes with the three ligands is L3>L2>L1. It can be explained by the relative energy gap between the lowest triplet energy level of the ligand (T) and 5D1 of Eu(III). This means that the triplet energy level of the ligand is the chief factor, which dominates Eu(III) complexes luminescence.

Synthesis and Characterization of 3,4-Diphenylmaleimide Copolymers That Exhibit Orange to Red Photoluminescence and Electroluminescence

A series of newly designed 3,4-diphenylmaleimide-based π-conjugated copolymers that exhibit red fluorescence in both solution and solid state were synthesized and characterized. Bright and efficient red fluorescence in the solid state was achieved by varying the structural combination of thiophene and/or fluorene with 3,4-diphenylmaleimide fluorophore. The range of thiophene- and fluorene-derived 3,4-diphenylmaleimide model compounds revealed that thiophene moieties were effective in extending the emission wavelength to the red region, and fluorene moieties significantly enhanced fluorescence intensity. Polymer light-emitting diodes (PLEDs) fabricated from 3,4-diphenylmaleimide−terthiophene copolymer (PTTML) exhibited saturated red electroluminescence (EL) with emission of 676 nm, although the diode was inefficient and dim. TPBI (2,2‘,2‘ ‘-(1,3,5-phenylene)-tris(1-phenyl-1H-benzimidazole)) as the electron-transporting layer in PLEDs was found to improve the performance of 3,4-diphenylmaleimide−bithiophene...