Guest Fluorophore Research Articles

Lanthanide metal-organic framework functionalized with 10-hydroxybenzo[h]quinoline for ratiometric sensing to real-time determine monophenolase activity through indicator displacement assay

Tyrosinase monophenolase activity plays a crucial role in various biological processes and industrial applications, making the development of continuous monophenolase assays highly significant. In this study, ratiometric fluorescence sensing using a dual-emission sensor was established to determine monophenolase activity in real-time by integrating indicator displacement assay with lanthanide metal-organic frameworks (MOFs). Europium MOFs functionalized with 10-hydroxybenzo[h]quinoline (HBQ) were fabricated by conjugating an HBQ guest fluorophore to the 3,5-dicarboxyphenylboronic acid (DBA) ligand using a solvothermal method. The conjugated HBQ served as an optical indicator at 510 nm with large Stokes shift, whereas the Eu-MOFs acted as a fluorescent internal standard at 616 nm for dual emission. DBA acts as an antenna ligand and provides a competitive receptor site for L-3,4-dihydroxyphenlalanine (L-DOPA) and HBQ. L-DOPA competitively binds to DBA owing to its higher affinity and displaces the conjugated HBQ, resulting in the quenching of HBQ and Eu-MOFs fluorescence. A linear change in the dual-emission intensity ratio was observed as a ratiometric response towards L-DOPA. The sensor quantified L-DOPA with a detection limit of 0.13 μM. Monophenolase activity was correlated with the real-time change in the ratiometric signal using L-DOPA as the product of the enzymatic reaction. A progression curve for the formation of L-DOPA was constructed to calculate the initial rate, yielding a low detection limit for monophenolase activity of 0.15 U·mL−1. The method has been successfully applied to real samples, kinetic studies, and high-throughput screening of inhibitors. This sensing platform opens a new avenue for determining tyrosinase activity.

Photoluminescent Silica Nanostructures and Nanohybrids.

The complicated photophysics of wide variety of defects existing in silica (SiO2 ) layer of nanometer thickness determines widespread photoluminescence bands of Si/SiO2 based system as well as SiO2 nanoparticles (NPs) for their applications in photovoltaic and optoelectronic devices. This review attempts to summarize different photophysical processes in pure SiO2 NPs. Moreover, these NPs also act as scaffolds for various guest molecules to perform their specific functions. Guest fluorophore molecules when trapped inside pores of SiO2 NPs exhibit a different photodynamics than free state, which opens up several important applications of hybrid SiO2 NPs in artificial photosynthesis, sensing, biology and optical fiber.

Excited state intramolecular proton transfer of 2-Aryl,3-Hydroxybenzo[g]quinolones in surfactant supramolecular assemblies

The 2-Aryl 3-Hydroxybenzo[g]quinolones (2Ar3HBQ) are a relatively new family of ESIPT fluorophores distinguished by their visible absorption spectra, which makes them potential ratiometric probes for biological media. In the present work, we found that 2Ar3HBQ residing as guest fluorophores inside biomimetic host systems like surfactant supramolecular assemblies like micelles and reverse micelles, exhibit dual emission attributable to ESIPT. Ratiometric analysis of the two emission peaks corresponding to the normal (N*) and tautomer (T*) species indicated that the ESIPT rates depend strongly on the nature of the host supramolecular assembly. For example, the ESIPT rate in reverse micelles containing no water was found to be similar to that in weak H-bonding and low polar solvents like acetonitrile. However, addition of water leads to the formation of water nano-droplets inside the reverse micelles, with concomitant sharp decrease of ESIPT rates. In each of the cases studied, the major factor determining the ESIPT rate appears to be the competition between intramolecular H-bonding within the guest fluorophore on the one hand, and intermolecular H-bonding involving the guest fluorophore and water molecules in its local environment, on the other hand.

Plastic scintillators with 1-phenyl-3-(mesityl)-2-pyrazoline as unique fluorophore for efficient neutron/gamma pulse shape discrimination

The development of highly efficient plastic scintillators for neutron/gamma pulse shape discrimination is a matter of current interest. This is generally achieved using two fluorophores, with one of them being added to the polymer formulation at a concentration higher than typically 15 weight percent (wt%). Here, we report our results concerning the development of highly performant poly(vinyltoluene)-based (PVT) plastic scintillators for efficient fast neutron/gamma pulse shape discrimination, using 1-phenyl-3-(mesityl)-2-pyrazoline (1) as the only guest fluorophore. On our route during this study, the synthesis of the compound 1 has been revisited. Analysis and evaluation of the radioluminescence properties of these novel PVT-based plastic scintillators containing compound 1 are also described. In particular their light output and neutron/gamma discrimination ability were characterized. The sample doped with 15 wt% of compound 1 has a light output of 0.65 relative to EJ-200 and a neutron/gamma discrimination figure of merit of 0.84 in the range 450–500 keVee.

Molecular Rotors as Guest Fluorophores Probing the Local Environment inside Host G4 Supramolecular Hydrogels

Fluorescent molecular rotors with a high binding affinity toward the guanosine quartet (G4) were incorporated as guest fluorophores into host supramolecular hydrogels based on the self-assembly of G4 units, to probe the local environment. Torsional dynamics of the rotors were severely inhibited inside the hydrogels in comparison with aqueous solutions, although the hydrogels were composed of >95% water. Moreover, even though all the gels were rigid bodies with no spontaneous deformation or flow property at room temperature, torsional dynamics in G4 borate gels was found to be consistently several orders of magnitude slower than those in the other G4 gels, irrespective of the identity of the molecular rotor probe. This clear difference in the molecular mobilities of the guest fluorophore could be attributed to systematic differences in the internal structure between the two categories of host G4 hydrogels. In specific terms, the borate groups in G4 borate hydrogels serve as bridging units between separate G4 quadruplex strands, generating additional cross-links that reinforce the network structure of the gel. The results demonstrate that molecular rotors act as efficient fluorescent probes for the quantitative assessment of the molecular-level environment and dynamics inside the hydrogels, an aspect that is missed out by most other analytical methods that are routinely employed for studying them.

Synthesis, Adsorption, and Recognition Properties of a Solid Symmetric Tetramethylcucurbit[6]uril-Based Porous Supramolecular Framework

In this work, we reported a porous supramolecular framework (A) constructed of a symmetric tetramethylcucurbit[6]uril (TMeQ[6]) in aqueous HCl solutions; the driving force was the outer surface interaction of cucurbit[n]urils, as well as hydrogen bonding between latticed water molecules and portal carbonyl oxygens of TMeQ[6]. Adsorption experimental results revealed that the porous supramolecular framework can absorb certain fluorophore guests (FGs) to form luminescent assemblies (FG@As) by fluorescence enhancement or colour change, and some of them can respond to certain volatile organic compounds. Thus, the TMeQ[6]-based supramolecular framework could be used as a sensor for certain gas or volatile compounds.

Specific Recognition of Methanol Using a Symmetric Tetramethylcucurbit[6]uril-Based Porous Supramolecular Assembly Incorporating Adsorbed Dyes

A symmetric tetramethylcucurbit[6]uril-based porous supramolecular assembly was prepared in an aqueous H2SO4 solution (5M). The driving force for the formation of this assembly is mainly the outer surface interaction of Q[n], which includes the ion-dipole interaction of SO42− anions and the positive electrostatic potential of the outer surface of the symmetric tetramethylcucurbit[6]uril (TMeQ[6]), the dipole-dipole interactions between the positive electrostatic potential of the outer surface of TMeQ[6] and portal carbonyl oxygens of TMeQ[6], and the hydrogen bonding between lattice water molecules and portal carbonyl oxygen atoms in TMeQ[6]. The TMeQ[6]-based porous supramolecular assembly exhibits the characteristics of absorbed fluorophore guests (FGs), such as dyes and polycyclic compounds with different fluorescence characteristics. Moreover, the resulting luminescent assemblies (FG@As) can respond to certain volatile organic compounds; in particular, the luminescent assemblies of rhodamine B or pyrene display a unique fluorescence enhancement in response to methanol.

Preparation and adsorption properties of a facile solid cucurbit[8]uril-based porous supramolecular assembly

Cucurbit[8]uril (Q[8]) was used as the building block for the facile preparation of Q[8]-based supramolecular assemblies in aqueous HCl solutions (A). The Q[8]-based supramolecular assembly was constructed of Q[8] molecules held together through outer surface interactions of cucurbit[ n]urils, and hydrogen bonding between latticed water molecules and portal carbonyl oxygens of Q[8]. The porous structure resulted in different adsorption properties for different fluorophore guests (FGs), including dyes and fused-ring compounds, and fluorescence enhancement or colour changes resulted in luminescent materials (FG@As). Moreover, some of the FG@A systems could selectively respond to certain volatile organic compounds, for which they can be used as solid sensors.

Unusual intermolecular charge transfer enables supramolecular fluorescent viscosity sensors

We propose and demonstrate a novel molecular design strategy to develop supramolecular fluorescent viscosity probes. Our new probes are constructed based on host-guest chemistry, in which the guest fluorophore itself is not a viscosity sensor. However, upon complexation with the host molecule, the resulted supramolecule exhibits unusual intermolecular charge transfer between the host and guest molecules. This intermolecular charge transfer drives molecular rotations and suppresses fluorescence output. As solvent viscosity increases from 1.1 cP to 612.6 cP, hindering molecular rotations leads to considerable fluorescence intensification by up to 21 times in our probes. Our design strategy opens a new avenue for developing fluorescent viscosity sensors.

Near-room-temperature phase-change fluorescent molecular rotor and its hybrids

A unique molecular rotor consisting of a tetraphenylethylene derivative with a paraffin wax-like long alkyl chain (TPE18) is synthesized and compared to other derivatives containing shorter alkyl chains. In differential scanning calorimetry, TPE18 shows an endothermic peak (enthalpy of fusion, ΔHfus = 55.3 J g−1) at 45 °C during the heating process and an exothermic peak at 38.6 °C during the cooling process. TPE18 exhibits critical changes in the fluorescence intensity and color during the crystal–melt phase change. TPE18 can be dissolved by an octadecane melt and then absorbed by filter paper. When the waxed paper is exposed to the heat sources of an IR laser or a finger, high-resolution fluorescence images of the characters and fingerprints appear on the paper. TPE18 also serves as a host matrix in a melt state that was easily mixed with the guest fluorophores of Alq3 and rubrene. Homogeneous hybrid solids with defined features are obtained without any significant segregation after cooling to room temperature. Fluorescence images with various colors are drawn onto the surfaces of glass slides or papers using the hybrids as crayons.

Metal-assisted selective recognition of biothiols by a synthetic receptor array.

A synergistic combination of a deep cavitand host, fluorophore guests and transition metal ions can be used to sense small molecule thiols of biological interest with good efficiency and selectivity in complex aqueous media.

A novel H-bonding self-assembly heteromeric molecular duplex bearing host and guest energy transfer units as high-performance electroluminescent material

Two oligoamide strands with complementary H-bonding sequences bearing 4HB-NIM and 4HB-CzNI were synthesized. 4HB-NIM and 4HB-CzNI could be self-assembled into a heterodimeric dyad (namely 4HB-NIM-CzNI)via quadruple H-bond interactions. Photoluminescence measurements revealed that in both dilute solution and doped film states, more efficient host-guest energy transfer processes could be observed in the duplex 4HB-NIM-CzNI than the physical blends of the small molecular guest reference compound NIM and the host single strand 4HB-CzNI, which should be attributed to the shortened spatial distances in 4HB-NIM-CzNI. In addition, in comparison with NIM and the guest single strand 4HB-NIM, 4HB-NIM-CzNI shows much higher photoluminescence quantum yield [0.53 vs 0.04 (NIM) or 0.35 (4HB-NIM)] in neat-film state, indicative of the more alleviated concentration quenching of the guest fluorophore in 4HB-NIM-CzNI than 4HB-NIM and NIM. As a consequence, an organic light-emitting diode (OLED) with 4HB-NIM-CzNI as the light-emitting dopant shows much more improved electroluminescent performance than its 4HB-NIM-based reference OLED: with lower turn-on voltage (5.0 vs 5.9 V), higher maximum luminance (5260 vs 2980 cd m−2) and current efficiency (3.5 vs 3.0 cd A−1) as well as lower efficiency roll-off. All these results indicated that the integration of both host and guest fluorophores into H-bonding self-assembled material should be an effective strategy to construct high performance supramolecular electroluminescent materials.

Spin-Dependent Exciton Funneling to a Dendritic Fluorophore Mediated by a Thermally Activated Delayed Fluorescence Material as an Exciton-Harvesting Host

Thermally activated delayed fluorescence (TADF) materials generate energetically equivalent spin-singlet and spin-triplet excited states. In the presence of an energy acceptor, each excited state undergoes energy transfer on different length scales. However, the lack of quantitative understanding of the length dependence of the excited energy-transfer processes hampers the rational design of molecular systems that control exciton transport in organic light-emitting diodes (OLEDs) using TADF. We herein utilize a dendritic fluorophore G1, which consists of an anthracene-based fluorescent core encapsulated by four insulating tris(4-tert-butylphenyl)methyl groups as an energy acceptor. By combining transient photoluminescence measurements and kinetic modeling, we demonstrate the spin-dependent energy transfer in a binary host–guest system composed of a TADF material as the exciton-harvesting host and G1 as the guest fluorophore. The encapsulated structure with the dendritic shell effectively inhibits triplet ...

Light-Controlled Selective Disruption, Multilevel Patterning, and Sequential Release with Polyelectrolyte Multilayer Films Incorporating Four Photocleavable Chromophores

We report photolabile polyelectrolyte multilayers (PEMs), produced by the layer-by-layer (LbL) approach, which comprise commercially available photoinert polyanions and photolabile polycations. Photochemical degradation of synthetic photolabile polycations renders these PEMs soluble in near neutral aqueous solutions. Taking advantage of the vast array of available photocleavable chromophores that absorb different wavelengths of light with different quantum yields of photolysis, we designed four photolabile polycations (P1–P4), each containing different photocleavable groups: dialkylaminocoumarin group (P1), different nitrobenzyl groups (P2 and P3), and methoxyphenacyl group (P4). PEMs containing different chromophores dissolved selectively under different irradiation conditions. Sequential photocontrolled dissolution of multilayers from a hybrid, quadruple-compartment LBL film was demonstrated using this approach, as was photolithographic patterning of films at multiple heights using different irradiation conditions and photomasks. We also demonstrated irradiation-selective, light-triggered release of guest fluorophores from microspheres coated with such PEMs.

Time-dependent fluorescence Stokes shift and molecular-scale dynamics in alginate solutions and hydrogels

Alginates are water-soluble polysaccharides that bind metal cations like Ca2+, producing hydrogels. Here, we have determined time-dependent fluorescence Stokes shift of a guest fluorophore to elucidate molecular length-scale local dynamics within alginate-based solutions and hydrogels. We find a major bulk water-like fast response emanating from large water pools interspersed between the polysaccharide chains, together with a minor but significant slow response. The possible origin of the latter is discussed in terms of either water molecules constituting the polysaccharide hydration shells or ion distribution and diffusion around the fluorophore dipole, or microscopic structural inhomogeneity inside the alginate-based media.

Tuning oxygen-sensing behaviour of a porous coordination framework by a guest fluorophore

A new oxygen-sensing material with desirable excitation/emission characteristics was achieved by using a simple guest fluorophore.

Photoisomerization and reorientational mobility of symmetric carbocyanines in AOT/alkane/polar solvent microemulsions

Molecular motion of carbocyanine fluorophores DOCI, DODCI and DTDCI were studied in AOT/n-heptane microemulsions containing added polar solvents: water, methanol or acetonitrile. The response varied remarkably depending on the nature of the fluorophore and polar solvent. When the amount of added polar solvent was low, molecular mobility was invariably retarded, due to a combination of electrostatic and hydrophobic forces that induce the guest fluorophore to cling to the AOT molecules of the host reverse micelle. However, at high amounts of added methanol or water, these interactions diminished considerably, causing increase in the mobility of the guest fluorophores up to different extents.

Energy Transfer in a Mechanically Trapped Exciplex

Host-guest complexes involving M(6)L(4) coordination cages can display unusual photoreactivity, and enclathration of the very large fluorophore bisanthracene resulted in an emissive, mechanically trapped intramolecular exciplex. Mechanically linked intramolecular exciplexes are important for understanding the dependence of energy transfer on donor-acceptor distance, orientation, and electronic coupling but are relatively unexplored. Steady-state and picosecond time-resolved fluorescence measurements have revealed that selective excitation of the encapsulated guest fluorophore results in efficient energy transfer from the excited guest to an emissive host-guest exciplex state.

Modification of Fluorophore Photophysics through Peptide-Driven Self-Assembly

We describe the formation of self-assembling nanoscale fibrillar aggregates from a hybrid system comprising a short polypeptide conjugated to the fluorophore fluorene. The fibrils are typically unbranched, approximately 7 nm in diameter, and many microns in length. A range of techniques are used to demonstrate that the spectroscopic nature of the fluorophore is significantly altered in the fibrillar environment. Time-resolved fluorescence spectroscopy reveals changes in the guest fluorophore, consistent with energy migration and excimer formation within the fibrils. We thus demonstrate the use of self-assembling peptides to drive the assembly of a guest moiety, in which novel characteristics are observed as a consequence. We suggest that this method could be used to drive the assembly of a wide range of guests, offering the development of a variety of useful, smart nanomaterials that are able to self-assemble in a controllable and robust fashion.

Fluorescent dye guest-host effects in advanced ferroelectric liquid crystals

Abstract Previous work has shown that guest-host ferroelectric systems incorporating dichroically absorbing dyes are suitable for use in colour display applications. These utilize either the dichroic absorption of a conventional dye, or the emission of a fluorescent dye. We present here the electrooptical properties of several advanced ferroelectric liquid crystals doped with a new fluorescent dye, coloured blue in emission. The data consists of measurements of tilt angle, response time, spontaneous polarization, and rotational viscosity, from which we conclude that certain hosts are not adversely affected by the fluorescent dopants. These results are then discussed in connection with the use of these mixtures in two novel colour display configurations, which are also presented, utilizing either the dichroic absorption or the polarized fluorescence of the fluorophore guests.