A novel path to luminescent hybrid molecular materials: modifying the hydroxyl group of 6‐hydroxynicotinic acid by grafting to a silica network

In this paper, a novel path was put forward to modify the hydroxyl group of 6‐hydroxynicotinic acid by 3‐(triethoxysilyl)‐propyl isocyanate and prepare the corresponding organic–inorganic molecular‐based hybrid material with the two components connected by covalent bonds. The bridging unit is a derivative of 6‐hydroxynicotinic acid that is utilized to coordinate to Tb³⁺ via hydrolysis and polycondensation processes with functional triethoxysilyl groups. Ultraviolet absorption, phosphorescence spectra and luminescence spectra were applied to characterize the photophysical properties of the hybrid material obtained and the spectroscopic data show that the triplet energy of modified 6‐hydroxynicotinic acid efficiently initiates the antenna effect and matches the emissive energy level of the metal ions. As a result, the intramolecular energy transfer process is completed within these molecular‐based hybrids. Copyright © 2005 John Wiley & Sons, Ltd.     

Terbium/zinc luminescent hybrid siloxane-oxide materials bridged by novel ureasils linkages

Covalently bonded silicate/modified aromatic acid luminescent composites have been prepared from 3-(triethoxysilyl)-propyl isocyanate (TEPIC) grafted salicylic acid and central metal ions (Tb, Zn). The existence of covalent linkages between TEPIC and silica matrices were realized by after hydrolysis and polycondensation processes of ethoxysilyl groups. Luminescence spectra were utilized to characterize the photophysical properties of the obtained hybrid material and the above spectroscopic data reveal that the triplet energy of modified salicylic acid in this favorable hybrid system matches with the emissive energy level of Tb³⁺. In addition, Zn containing hybrids exhibit a broad band around 420 nm which may be beneficial to fabricate blue emission materials.     

Molecular design and photo-physics of quaternary hybrid terbium centered systems with novel functional di-urea linkages of strong chemical bonds through hydrogen transfer addition

Two kinds of crosslinking reagents, 3-aminopropyl-methyl-diethoxylsiliane (H₂N(CH₂)₃SiCH₃(OC₂H₅)₂, abbreviated as APMES) and N-2-aminoethyl-3-aminopropyltriethoxylsiliane (H₂N(CH₂)₂HN(CH₂)₃Si(OC₂H₅)₃, abbreviated as AEAPES) are modified by 3-(triethoxysilyl)-propyl isocyanate (TESPIC) to afford two novel crosslinking molecular derivatives as bridge ligands. Then the ternary organic-inorganic molecular-based hybrid system with these functional bridge ligands and 1,10-phenanthroline (phen) are constructed with the two components equipped with covalent bonds. The two components of APMES (or AEAPES) and TESPIC is linked through -NHC(O)NH- groups which is applied to coordinate to Tb³⁺ and further formed Si-O backbones after co-hydrolysis and co-polycondensation processes, while phen behaves as the main energy donor for the sensitization of luminescence of Tb³⁺. Luminescence spectra were utilized to characterize the photo-physical properties of the obtained hybrid system and the above spectroscopic data reveal that the phen in this favorable hybrid system behaves the main energy donor for the luminescence of Tb³⁺. In this way, the intra-molecular energy transfer process took place within these molecular-based hybrids and strong green and blue emissions of Tb³⁺ have been achieved.     

Optically hybrid lanthanide ions (Eu3+, Tb3+)‐centered materials with novel functional di‐urea linkages

The synthesis of 3‐(triethoxysilyl)‐propyl isocyanate (TEPIC) modified by (3‐aminopropyl)triethoxysilane (APS) and the preparation of the corresponding organic–inorganic molecular‐based hybrid material with the two components equipped with covalent bonds is described. The coupling agent moiety is a convolution of TEPIC and APS through ? NHC(?O)NH? groups, which is applied to coordinate to RE³⁺ and further formed Si? O backbones after hydrolysis and polycondensation processes. For comparison and luminescence efficiency purposes, we added 2,2‐bipyridyl to the above hybrids in order to increase the conjugating effects and sensitize rare earth ions emissions. Luminescence spectra were utilized to characterize the photophysical properties of the hybrid material obtained, and the above spectroscopic data reveal that the triplet energy of 2,2‐dipyridyl in this favorable hybrid system matches with the emissive energy level of RE³⁺. In this way, the intramolecular energy transfer process took place within these molecular‐based hybrids and strong green and red emissions of RE³⁺ have been achieved. Copyright © 2005 John Wiley & Sons, Ltd.     

Chemically Bonded Hybrid Systems from Functionalized Hydroxypyridine Molecular Bridge: Characterization and Photophysical Properties

A series of novel photoactive hybrid materials with organic parts covalently linked to inorganic parts via the acylamino group have been assembled by sol–gel process. The organic parts as molecular bridge derive from α-hydroxypyridine (HP) functionalized by 3-(triethoxysilyl)-propyl isocyanate (TESPIC). Finally homogeneous, molecular-based hybrid materials with different microstructure (uniform spherical or clubbed) are obtained, in which no phase separation is observed. This may be ascribed as the different coordination behavior of metal ions (Eu³⁺ (Tb³⁺) or Zn²⁺). Red emission of Eu–HP–Si, green emission of Tb–HP–Si and violet-blue luminescence of Zn–HP–Si hybrids can be achieved within these molecular-based hybrid materials. Besides, both Eu(Tb) and Zn are introduced into the same hybrid systems (Eu(Zn)–HP–Si or Tb(Zn)–HP–Si) through the covalent Si–O bond, whose sphere particle size can be modified. Especially the photoluminescence behavior can be enhanced, suggesting that intramolecular energy transfer takes place between inert Zn²⁺ and Eu³⁺ (Tb³⁺) in the covalently bonded hybrid systems.     

Luminescent lanthanide molecular‐based hybrid materials bridged through novel urethane linkages

Novel organosilicates with covalently linked functional modified aromatic acid have been synthesized from 3‐aminopropyl triethoxysilane (APS) grafted 4‐ethoxy benzoic acid (EB‐Si) and terbium ions via a simple low‐temperature route. The existence of covalent bonds between EB‐Si and silica matrices was shown by the hydrolysis and polycondensation processes of ethoxysilyl groups. Luminescence spectra were used to characterize the photophysical properties of the obtained hybrid material and the above spectroscopic data reveal that the triplet energy of modified para ethoxy benzoic acid in this favorable hybrid system matches the emissive energy level of RE³⁺. Copyright © 2006 John Wiley & Sons, Ltd.     

Mesoporous hybrids containing Eu complexes covalently bonded to SBA-15 functionalized: Assembly, characterization and photoluminescence

A novel series of luminescent mesoporous organic-inorganic hybrid materials has been prepared by linking Eu³⁺ complexes to the functionalized ordered mesoporous SBA-15 which was synthesis by a co-condensation process of 1,3-diphenyl-1,3-propanepione (DBM) modified by the coupling agent 3-(triethoxysilyl)-propyl isocyanate (TEPIC), tetraethoxysilane (TEOS), Pluronic P123 surfactant as a template. It was demonstrated that the efficient intramolecular energy transfer in the mesoporous material Eu(DBMSi-SBA-15)₃phen mainly occurred between the modified DBM (named as DBM-Si) and the central Eu³⁺ ion. So the Eu(DBMSi-SBA-15)₃phen showed characteristic emission of Eu³⁺ ion under UV irradiation with higher luminescence quantum efficiency. Moreover, the mesoporous hybrid materials exhibited excellent thermal stability as the lanthanide complex was covalently bonded to the mesoporous matrix.     

Chemically bonded metallic (Eu, Tb, Zn) hybrid materials through sulfide linkage: Molecular construction, physical characterization and photophysical properties

In this paper, a kind of aromatic carboxylic acid of sulfhydryl group (2-mercaptonicotinic acid) is modified with four silane crosslinking reagents (3-methacryloyloxypropyltrimethoxysilane (S₁), 3-glycidoxypropyltrimethoxysilane (S₂), 3-aminopropyltrimethoxysilane (S₃), and 3-(triethoxysilyl)propylisocyanate (S₄)) to achieve four new kinds of functionalized molecular bridge (P_i (i = 1-4)). Subsequently, four molecular bridges and lanthanides (europium and terbium) or zinc ions have been assembled via chemical bonds through a sol-gel (cohydrolysis and copolycondensation) process with inorganic precursor (tetraethoxysilane, TEOS), resulting in four novel series of chemically bonded hybrid materials which named as Ln (Zn)-M_i (i = 1-4). The coordinated bonding makes metal ions evenly dispersed in a stable hybrid system. The intramolecular energy transfer process between lanthanide ions and the molecular bridges take place within these molecular-based hybrids and especially the luminescent quantum efficiency of them are determined, suggesting that the hybrid material systems derived from different molecular bridges present different luminescence efficiencies.     

Design of a Novel Sort of Luminescent Terbium(III) Hybrid Materials with Potential Molecular Bridge

Summary. A kind of precursor molecule (abbreviated as EPDA–APMS) was synthesized by means of the amidation reaction of 5-ethylpyridine-2,3-dicarboxylic acid (EPDA) with a crosslinking molecule (3-aminopropyl)trimethoxysilane (APMS). Then the hybrid materials were obtained by reaction of this kind of monomer (EPDA–APMS), tetraethoxysilane (TEOS) and Tb(NO₃)₃·6H₂O by an in-situ sol-gel process, resulting in a novel molecular hybrid material (named as Tb–EPDA–APMS) with double chemical bonds (Tb–O coordination bond and Si–O covalent bond). Ultraviolet absorption, phosphorescence, and fluorescence spectra were applied to characterize the photophysical properties of the obtained hybrid material. The strong luminescence of Tb³⁺ substantiates optimum energy match and effective intramolecular energy transfer between the triplet state energy of modified ligand bridge and emissive energy level of Tb³⁺.     

Design of a Novel Sort of Luminescent Terbium(III) Hybrid Materials with Potential Molecular Bridge

A kind of precursor molecule (abbreviated as EPDA–APMS) was synthesized by means of the amidation reaction of 5-ethylpyridine-2,3-dicarboxylic acid (EPDA) with a crosslinking molecule (3-aminopropyl)trimethoxysilane (APMS). Then the hybrid materials were obtained by reaction of this kind of monomer (EPDA–APMS), tetraethoxysilane (TEOS) and Tb(NO₃)₃·6H₂O by an in-situ sol-gel process, resulting in a novel molecular hybrid material (named as Tb–EPDA–APMS) with double chemical bonds (Tb–O coordination bond and Si–O covalent bond). Ultraviolet absorption, phosphorescence, and fluorescence spectra were applied to characterize the photophysical properties of the obtained hybrid material. The strong luminescence of Tb³⁺ substantiates optimum energy match and effective intramolecular energy transfer between the triplet state energy of modified ligand bridge and emissive energy level of Tb³⁺.     

From chemistry to materials, design and photophysics of functional terbium molecular hybrids from assembling covalent chromophore to alkoxysilanes through hydrogen transfer addition

Two silica-based organic-inorganic hybrid materials composed of phenol (PHE) and ethyl-p-hydroxybenzoate derivatives (abbreviated as EPHBA) complexes were prepared via a sol-gel process. The active hydroxyl groups of PHE/EPHBA grafted by 3-(triethoxysilyl)-propyl isocyanate (TESPIC) through hydrogen transfer reaction were used as multi-functional bridged components, which can coordinate to Tb³⁺ with carbonyl groups, strongly absorb ultraviolet and effectively transfer energy to Tb³⁺ through their triplet excited state, as well as undergo polymerization or crosslinking reactions with tetraethoxysilane (TEOS), for anchoring terbium ions to the silica backbone. For comparison, two doped hybrid materials in which rare-earth complexes were just encapsulated in silica-based sol-gel matrices were also prepared. NMR, FT-IR, UV/vis absorption and luminescence spectroscopy were used to investigate the obtained hybrid materials. UV excitation in the organic component resulted in strong green emission from Tb³⁺ ions due to an efficient ligand-to-metal energy transfer mechanism.     

Photophysical properties of terbium molecular-based hybrids assembled with novel ureasil linkages

Three silica-based organic-inorganic hybrid systems composed of hydroxyl aromatic derivatives (2-acetylphenol [HAP], 2-hydroxy-3-methylbenzoic acid [HMBA], 3-hydroxy-meta-phthalic acid [HMPHTH] complexes) were prepared via a sol-gel process. The active hydroxyl groups of the three ligands grafted by 3-(triethoxysilyl)-propyl isocyanate (TESPIC) through hydrogen transfer addition reaction were used as multi-functional bridge components, which can coordinate to Tb3+ with carbonyl groups, strongly absorb ultraviolet light and effectively transfer energy to Tb3+ through their triplet excited state, as well as undergo polymerization or crosslinking reactions with tetraethoxysilane (TEOS), for anchoring terbium ions to silica backbone. NMR, FT-IR, UV-vis absorption, luminescence spectroscopy was used to investigate the obtained hybrid material. UV excitation in the organic component resulted in strong green emission from Tb3+ ions due to an efficient ligand-to-metal energy transfer mechanism.     

Photophysical Properties of a Novel Organic–Inorganic Hybrid Material: Eu(III)-β-Diketone Complex Covalently Bonded to SiO2/ZnO Composite Matrix

In this article, dibenzoylmethane (DBM) was first grafted with the coupling reagent 3-(triethoxysilyl)-propyl isocyanate (TESPIC) to form precursor DBM–Si, and ZnO quantum dot was modified with 3-mercaptopropyltrimethoxysilane (MPS) to form SiO₂/ZnO nanocomposite particle. Then the precursor DBM–Si and the terminal ligand 1,10-phenthroline (phen) were coordinated to Eu³⁺ion to obtain ternary hybrid material phen–Eu–DBM–SiO₂/ZnO after hydrolysis and copolycondensation between the tetraethoxysilane (TEOS), water molecules and the SiO₂/ZnO network via the sol–gel process. In addition, for comparison, the binary hybrid material with SiO₂/ZnO network and ternary hybrid material with pure Si–O network were also synthesized, denoted as Eu–DBM–SiO₂/ZnO and phen–Eu–DBM–Si, respectively. The results reveal that hybrid material with SiO₂/ZnO network phen–Eu–DBM–SiO₂/ZnO exhibits the stronger red light, the longer lifetimes and higher quantum efficiency than hybrid material with pure Si–O network phen–Eu–DBM–Si, suggesting that SiO₂/ZnO is a favorable host matrix for the luminescence of rare earth complexes.     

Luminescent Hybrid Ionogels Functionalized with rare Earth fluoride Up‐conversion Nanocrystals Dispersing in Ionic Liquid

Rare earth doped fluorides (BaMgF₄, aYF₄ and BaYF₅/BaLuF₅) have been synthesized and dispersed in an ionic liquid compound, (3‐triethoxysilyl) propyl‐3‐methylimidazolium chloride (denoted as IM⁺Cl ^? ). Through the cohydrolysis and copolycondensatoin reaction between the alkoxy group (3‐triethoxysilyl) of IM⁺ and tetraethoxysilane in the presence of carboxylic acids (formic acid) as catalyst and water source, luminescent hybrid ionogels form subsequently. ¹H NMR spectroscopy, X‐ray diffraction, transmission electron microscopy, scanning electron microscopy and especially up‐conversion (UC) luminescence spectroscopy are used to characterize the precursors and the resulted hybrid ionogels. These hybrid ionogels exhibit the UC luminescence properties of immobilized rare earth fluoride nanocrystals (BaMgF₄, NaYF₄ and BaYF₅/BaLuF₅) doped Er³⁺/Tm³⁺, Yb³⁺.     

Coordination bonding assembly and photophysical properties of Europium organic/inorganic/polymeric hybrid materials

Ternary organic/inorganic/polymeric hybrid material PVP-Eu-(DBM-Si)₃ (DBM = dibenzoylmethane; PVP = poly(4-vinylpyridine)) have been synthesized through the coordination bonds. The precursor DBM-Si is obtained by the modification of DBM molecule with a cross-linking reagent TEPIC (3-(triethoxysilyl)-propyl isocyanate), which is used to form the inorganic Si–O–Si networks with TEOS (tetraethoxysilane) after a hydrolysis and polycondensation process. PVP, which is obtained through the polymerization reaction using 4-vinylpyridine as the monomer in the presence of BPO (benzoyl peroxide), is used to form the organic polymeric C–C chains. For comparison, the binary organic/inorganic hybrid material Eu-(DBM-Si)₃ was also synthesized simultaneously. FT-IR (Fourier-transform infrared spectra), UV (ultraviolet absorption spectra), UV-DR (ultraviolet–visible diffuse reflection absorption spectra), SEM (scanning electron micrograph), PL (photoluminescence spectroscopy) and LDT (luminescence decay time) measurements are used to investigate the physical properties of the obtained hybrid materials. The results reveal that the ternary hybrids presents more regular morphology, higher red/orange ratio, stronger luminescent intensity, higher ⁵D₀ luminescence quantum efficiency and longer lifetime than the binary one, suggesting the property of the overall hybrid system is improved with the introduction of the organic polymer PVP.     

Luminescent organic–inorganic hybrid materials based on lanthanide containing ionic liquids and sylilated β-diketone

In this work, we report the luminescent organic–inorganic hybrid materials prepared by hydrolysis and condensation of sylilated β-diketone under acid conditions in the presence of carboxyl-functionalized ionic liquid in which Eu³⁺ ions are coordinated to the oxygen atoms of carboxylate groups from the ionic liquids. The obtained materials were characterized with FT-IR, TG and photoluminescence spectroscopy. FT-IR spectra imply that Eu³⁺ ions are still coordinated to the ionic liquid in the hybrid materials. Excitation and emission spectra demonstrate that the energy transfer occurs from the β-diketone molecules covalently bonded with silica to Eu³⁺ ions. The Eu³⁺ (⁵D₀) quantum efficiency value of the hybrid materials has been estimated based on the emission spectrum and the value of lifetime. A large value of ratio (16.44) between the intensities of the ⁵D₀→⁷F₂ and ⁵D₀→⁷F₁ transition and high value of ⁵D₀ quantum efficiency (51.01%) are obtained.     

Molecular design of luminescent organic-inorganic hybrid materials activated by europium (III) ions

Luminescent hybrid materials consisting in rare-earth (Eu³⁺, Gd³⁺) organic complexes covalently attached to a silica-based network have been obtained by a sol–gel process. Four dicarboxylic acids with different aromatic subunits (dipicolinic acid, 4-phenyl-2,6-pyridinedicarboxylic acid, 4-(phenylethynyl)-2,6-pyridinedicarboxylic acid and 2,6-Bis(3-carboxy-1-pyrazolyl)pyridine) have been chosen as ligands for Ln³⁺ ions. They were grafted to 3-aminopropyltriethoxysilane (APTES) to give organically modified alkoxysilanes that were used as molecular precursors for the preparation of hybrid materials. Ln³⁺ first coordination sphere, composition of the siloxane matrix and connection between the organic and inorganic parts have been characterized by infrared spectroscopy, by ¹³C²⁹Si solid-state NMR as well as by elemental analyses. UV excitation in the organic component resulted in strong emission from Eu³⁺ ions due to an efficient ligand-to-metal energy transfer. As compared to reference organic molecules, hybrid samples exhibited similar emission properties under UV excitation in addition to mainly unchanged excited states lifetimes. However, by direct excitation of the Eu³⁺-⁵D₀ energy level, the presence of two different site distributions were evidenced in the four hybrid compounds. Emission features related to each of these site distributions and their respective attribution were investigated. Variations in the relative emission intensities were observed according to the nature of the organic chromophore. These variations were discussed in relation to the ATE (Absorption-Transfer-Emission) mechanism and to the relative energy positions of the ligand and the rare-earth ions respectively.     

Synthesis and photophysical properties of novel organic–inorganic hybrid materials covalently linked to a europium complex

A novel sol–gel derived hybrid material (classed as Eu-DBM-Si) covalently grafted with Eu(DBM-OH)₃·2H₂O (where DBM-OH = o-hydroxydibenzoylmethane) was prepared through the primary β-diketone ligand DBM-OH. All the synthesized ligands were characterized by ¹H NMR, elemental analyses and Fourier transform infrared spectra (FTIR). The resultant Eu-DBM-Si material exhibited good transparent and homogenous property. Compared to the Eu-DBM hybrid prepared by physically doped silicon dioxide with Eu(DBM-OH)₃·2H₂O, the Eu-DBM-Si hybrid presented more efficient ligand-to-Eu³⁺ energy transfer and a significant improvement in the measured emission quantum yield. Furthermore, the photophysical properties of these hybrid materials, such as the photoluminescence (PL) spectra, PL intensities, symmetry properties, lifetime decays, and Judd-Ofelt parameters were also investigated in detail.     

Synthesis and characterization of graphene oxide‐based hybrid ligand and its metal complexes: Highly efficient sensor and catalytic properties

A new graphene oxide‐based hybrid material (HL) and its Co(II), Cu(II) and Ni(II) metal complexes were prepared. Firstly, graphene oxide and (3‐aminopropyl)trimethoxysilane were reacted to give graphene oxide–3‐(aminopropyl)trimethoxysilane (GO‐APTMS) hybrid material. After that, hybrid material HL was synthesized from the reaction of GO‐APTMS and 2,6‐diformyl‐4‐methylphenol. Finally, Co(II), Cu(II) and Ni(II) complexes of HL were obtained. All the materials were characterized using various techniques. The chemosensor properties of HL were investigated against Na⁺, K⁺, Cd²⁺, Co²⁺, Cu²⁺, Hg²⁺, Ni²⁺, Zn²⁺, Al³⁺, Cr³⁺, Fe³⁺ and Mn³⁺ ions and it was found that HL has selective chemosensing to Fe³⁺ ion. All the graphene oxide‐supported complexes were used as heterogeneous catalysts in the oxidation of 2‐methylnaphthalene (2MN) to 2‐methyl‐1,4‐naphthoquinone (vitamin K₃, menadione) in the presence of hydrogen peroxide, acetic acid and sulfuric acid. The Cu(II) complex showed good catalytic properties compared to the literature. The selectivity of 2MN to vitamin K₃ was 60.23% with 99.75% conversion using the Cu(II) complex.     

Hybrid materials of MCM-41 functionalized by lanthanide (Tb, Eu) complexes of modified meta-methylbenzoic acid: Covalently bonded assembly and photoluminescence

Novel organic-inorganic mesoporous hybrid materials were synthesized by linking lanthanide (Tb³⁺, Eu³⁺) complexes to the mesoporous MCM-41 through the modified meta-methylbenzoic acid (MMBA-Si) using co-condensation method in the presence of the cetyltrimethylammonium bromide (CTAB) surfactant as template. The luminescence properties of these resulting materials (denoted as Ln-MMBA-MCM-41, Ln=Tb, Eu) were characterized in detail, and the results reveal that luminescent mesoporous materials have high surface area, uniformity in the ordered mesoporous structure. Moreover, the mesoporous material covalently bonded Tb³⁺ complex (Tb-MMBA-MCM-41) exhibits the stronger characteristic emission of Tb³⁺ and longer lifetime than Eu-MMBA-MCM-41 due to the triplet state energy of organic legend MMBA-Si matches with the emissive energy level of Tb³⁺ very well.