Photoinduced Electron Transfer Effect Research Articles

Highly sensitive and selective paper sensor based on carbon quantum dots for visual detection of TNT residues in groundwater

Nowadays, selective, sensitive and visual detection of 2,4,6-trinitrotoluene (TNT) explosives residues in groundwater system has been a great challenge for human security. Herein, a visual fluorescence paper sensor for accurate and on-site detection of TNT in groundwater system by linking the recognition molecule onto the surface of the carbon quantum dots (CDs) was introduced. The fluorescence of CDs based nanosensor can be selectively and efficiently quenched by TNT through a photo-induced electron transfer effect between primary amino groups and TNT explosives. The fluorescence quantum yield of this kind of nanosensor is up to 32.25％ and the detection limit reaches as low as 0.213μmol/L. The interference molecules, such as the nitrobenzene derivatives have no influence on the sensitive detection of TNT. Furthermore, the paper sensor based on the CDs probe has been prepared, which can efficiently detect TNT residues in groundwater system. This developed nanosensor possesses the great capability of on-site and visual detection of TNT residues in groundwater without any further processing step.

Vinylanthracene-Based Compounds as Electron-Rich Sensors for Explosives Recognition.

Four new vinylanthracene-based fluorescent molecules were synthesized and characterized. The highly fluorescent vinylanthracene moiety was coupled with the ethynylbenzene group to yield rigid and electron-rich π systems, which were utilized as selective and sensitive probes for picric acid in both the solution and solid states. In solution, the molecules demonstrated signal amplification by a combined effect of photo-induced electron transfer and resonance energy transfer, whereas in the solid state the enhanced sensitivity was attributed to a collective effect of PET and exciton migration among closely spaced molecules. In direct contact mode experiments, thin films of the molecules demonstrated discernible changes in fluorescent intensity, which shows that the molecules are potential materials for in-the-field applications.

Diaminodibenzoxanthenium based near infrared pH probes with lower pKa

The fluorescent pH probes, 3,11-diamino-7-(4-(diethylamino)-phenyl)- dibenzo[c,h]xanthen-14-ium trifluoromethanesulfonate (1a) and 3,11-bis-(diethylamino)-7-(4-(diethylamino)phenyl)dibenzo[c,h]xanthen-14-ium trifluoromethanesulfonate (1b), were reported as pH probes worked in strong acidic conditions. Probes 1a–b were prepared by one-step condensation with 4-diethylaminobenzaldehyde and aminonaphthalen-1-ol derivatives, their absorption maxima gave slight changes between neutral and acidic conditions, and they exhibited pH-dependent near-infrared OFF–ON emission in the range of pH 2.0–5.0 with increasing fluorescent intensities of 272 and 114 folds, the calculated pKa values were 3.28 and 3.24 for probe 1a and probe 1b, respectively. The probes also showed excellent selectivity toward proton over other interferents in the selectivity and competition assays. The photoinduced electron transfer effect from diethylaminophenyl group to dibenzoxanthenium skeleton was proposed and further verified by theoretical calculation. The work indicates that dibenzoxanthenium would be a near-infrared fluorophore for probe design.

Polyurethane-based Eu(iii) luminescent foam as a sensor for recognizing Cu2+ in water

A novel porous polymer material with red emissions composed of a europium silica hybrid and polyurethane foam has been assembled. Its sensing properties in water have been investigated and the fluorescence of the foam was selectively quenched in the presence of Cu2+ (detection limit 3.4 μM) compared with other cation ions (Li+, Na+, K+, Mg2+, Ca2+, Ba2+, Cr2+, Mn2+, Co2+, Ni2+, Zn2+, Cd2+, Hg2+, Al3+, Pb2+ and Ag+). The high selectivity and sensitivity were attributed to the strong chelation of Cu2+ with nitrogen atoms of the ligand (L) and the photo-induced electron transfer effect. The luminescent polyurethane foam showed a good reusability (more than 10 times). Interestingly, the red emission can be switched “off” and “on” via the addition of copper ions and EDTA, respectively. Additionally, the tensile failure tests proved that higher mechanical strength could be achieved in the silica material reinforced polyurethane foam.

Computational investigations into new fluorescence quenching process induced by complexation of alkali metal ion

A novel fluorescent switchable chemosensor 1, which is composed of an anthracene-modified calix[4]crown in the 1,3-alternate conformation, was calculated by density functional theory and time-dependent density functional theory method. Geometries, molecular orbitals and binding thermal energies were evaluated at the restricted hybrid Becke's three-parameter exchange functional using 6-31 G(d) basis set and relativistic effective core potentials. The metal–ligand and cation–π interactions were investigated acting as two main types of driving force. Our calculations clearly show that solvent effects strongly influence cation selectivity, and K+ selectivity is recovered when even a few waters of hydration are considered. The calculations indicate that because of the photoinduced electron transfer effect, the addition of alkali metal ions have hardly any effect on the fluorescence of ligand 1 under neutral or basic conditions. Also, the high selectivity of ligand 1 for K+ and Rb+, under acidic conditions, the complexed metal ion can result in ammonium ion deprotonation, which leads to quenching of fluorescence of 1•H+. Copyright © 2012 John Wiley & Sons, Ltd.

A new detector for metal cations based on the combined effect of photoinduced electron transfer and a light harvesting system

A new tripod comprising three 1,8-naphthalimide units having different substituents at C-4 of the naphthalimide structure has been synthesized. The new dendron has two 4-ethoxy-1,8-naphthalimide units as an energy donor and a 4- N, N-dimethialaminoethilenidamino-1,8-naphthalimide acceptor to facilitate the donor–acceptor energy transfer. The main photophysical characteristics of the dendron have been studied in organic solvents of different polarity. The established energy transfer efficiency of is about 99% revealing the excellent antenna capacities of the dendron. The fluorescence intensity of the dendron has been studied in an acetonitrile solution in the presence of metal ions of various nature (Cu 2+, Co 2+, Zn 2+, Ni 2+, and Pb 2+) using two different excitation wavelengths of 365 nm and 435 nm. The detection limit of metal cations has been determined.

The design and synthesis of a novel 1,8-naphthalimide PAMAM light-harvesting dendron with fluorescence “off-on” switching core

A novel polyamidoamine dendron core, peripherally functionalized with 1,8-naphthalimide fluorophores, was configured as a light harvesting antenna in which the system surface was labelled with blue emitting 4-allyloxy-1,8-naphthalimide “donor” dyes capable of both absorbing light and efficiently (96%) transferring the energy to a single, yellow-green emitting 4- N-methylpiperazinyl-1,8-naphthalimide “acceptor” dye. The 1,8-naphthalimide core was designed on the “fluorophore-spacer-receptor” format and was able to function as a fluorescence photoinduced electron transfer sensor. Two different photoinduced electron transfer effects were observed in the new antenna namely that from the receptor to the core fluorophore and that from the polyamidoamine backbone to the peripheral 1,8-naphthalimides. Althogh the core emission intensity of the system was enhanced > four times by reducing the pH from 10 to 2, the fluorescence enhancement of the system in acidic medium, excited within the periphery ( λ ex = 360 nm), was approximately twice that of the core fluorescence enhancement after direct excitation of the focal 1,8-naphthalimide ( λ ex = 420 nm), because of more efficient energy transfer. The observed “off-on” switching of the core fluorescence over a wid pH scale indicates that the novel light harvesting antenna would be able to act as a highly efficient fluorescent sensor.

Photoinduced electron transfer and surface plasmon resonance in materials consisting of pyrene fluorophore and Au nanorods immobilized on MCM-48 surface

Mesoporous silica of the MCM-48 type as a support for fluorophore molecules was functionalized with 3-aminopropyl and 3-thiolopropyl groups. Then, molecules consisting of a fluorophore pyrene group and receptor fragments with donor N and O atoms were covalently attached by grafting of carboxyl groups to amino groups on a mesoporous silica surface. Additionally, Au nanorods were attached to thiol groups on the same surface. The vicinity of Au nanorods in a material with pyrene derivatives covalently grafted on the functionalized MCM-48 silica enhanced fluorescence of the composite material due to the surface plasmon resonance effect. The fluorescence emission of the prepared recognition material is quenched specifically owing to the photoinduced electron transfer effect after coordination reactions with Cu(II) ions. Moreover, the material exhibits selectivity for Cu(II) cations in aqueous solutions in presence of such metal ions as: alkali, alkaline earth, transition and heavy metals. During UV irradiation the studied material undergoes slowly photochemical degradation as a potential recognition element.

Photovoltaic and Electroluminescence Characters in Hybrid ZnOand Conjugated Polymer Bulk Heterojunction Devices

We report electroluminescence in hybrid ZnO and conjugated polymerpoly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene](MDMO-PPV) bulk heterojunction photovoltaic cells. Photoluminescencequenching experimental results indicate that the ultrafast photoinducedelectron transfer occurs from MDMO-PPV to ZnO under illumination. Theultrafast photoinduced electron transfer effect is induced because ZnOhas an electron affinity about 1.2 eV greater than that of MDMO-PPV.Electron `back transfer' can occur if the interfacial barrier betweenZnO and MDMO-PPV can be overcome by applying a substantial electricfield. Therefore, electroluminescence action due to the fact that theback transfer effect can be observed in the ZnO:MDMO-PPV devices sincea forward bias is applied. The photovoltaic and electroluminescenceactions in the same ZnO:MDMO-PPV device can be induced by differentinjection ways: photoinjection and electrical injection. The devicesare expected to provide an opportunity for dual functionality deviceswith photovoltaic effect and electroluminescence character.

Radical-ion mechanism of optical limiting in fullerene solutions

The effect of photoinduced electron transfer with formation of a radical-ion pair on the characteristics of optical limiting of laser radiation in specially prepared multi-component fullerene solutions is studied. The limitation efficiency in such solutions increases due to absorption of laser radiation by molecules in a metastable state. The experimental results show that the spectral and time optical limiting ranges can be expanded due to formation of radical ions.

Large Acceleration Effect of Photoinduced Electron Transfer in Porphyrin−Quinone Dyads with a Rigid Spacer Involving a Dihalosubstituted Three-Membered Ring

To understand the contribution of spacer structure toward electron transfer (ET) and to regulate electronic coupling between a redox pair, porphyrin−spacer−benzoquinone molecules were prepared where spacers are trans-decalin and dihalosubstituted tricyclo[4.4.1.0]undecane including a three-membered ring. These compounds were designed to have almost the same separation distance between a redox pair, the same number of intervening bonds, and the nearly equal free energy change associated with the ET reaction. The ET rates for the charge separation process were evaluated on the basis of the fluorescence lifetimes. A quite large difference in the ET rates was observed among these compounds, and the ET rates for the compounds having the three-membered rings were ca. 50 to 60 times larger than that with trans-decalin spacer in THF. From the analysis of temperature dependence of the ET rates, it was shown that the observed rate acceleration is caused by both an increase of the electronic coupling and a decrease of the reorganization energy. Ab initio calculations of the electronic coupling elements and on molecular orbitals for the cyclopropanes predicted that the former may be due to the enhancement of the ET pathways arising from the bent geometry of the spacer or of the mixing pathway induced by a very low lying antibonding orbital in the dihalosubstituted cyclopropane.

Sensitization of the photoconductivity of conducting polymers by C60: Photoinduced electron transfer.

We have investigated the effect of photoinduced electron transfer on the photoconductivity (PC) of conducting polymer-${\mathrm{C}}_{60}$ films by comparing the photoconductivity (carrier generation and carrier transport) of the conducting polymer sensitized with ${\mathrm{C}}_{60}$ with that of the conducting polymer alone. We present time-resolved transient PC results, subnanosecond to 0.5 \ensuremath{\mu}s, obtained from poly[2-methoxy,5-(2'-ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV) and poly(3-octylthiophene) (P3OT), and from conducting polymer films sensitized with several concentrations of ${\mathrm{C}}_{60}$. Both the magnitude and the lifetime of the transient PC increase substantially on increasing the concentration of ${\mathrm{C}}_{60}$. The results imply that quantum efficiency for photogeneration of charge carriers is increased by photoinduced electron transfer and that early time recombination is inhibited by the spatial separation of the electron and hole on the ${\mathrm{C}}_{60}$ and the conducting polymer, respectively. The greater enhancement of the transient PC in MEH-PPV (nearly two orders of magnitude with the addition of a few percent of ${\mathrm{C}}_{60}$) than in P3OT (nearly one order of magnitude with the addition of a comparable amount of ${\mathrm{C}}_{60}$) suggests a higher probability of early time recombination in pristine MEH-PPV. As a result of the enhancement in the photogeneration efficiency and the carrier lifetime, the spectral response of the steady-state PC in both MEH-PPV/${\mathrm{C}}_{60}$ and P3OT/${\mathrm{C}}_{60}$ films is significantly enhanced throughout the entire spectral range from the near infrared to the ultraviolet.