A deep-red xanthene-based highly sensitive fluorescent probe for detection of hypochlorite.

As an oxidant, deodorant and bleaching agent, the hypochlorous acid (HClO) and hypochlorite (ClO- ) are widely used in corrosion inhibitors, textile dyes, pharmaceutical intermediates and in our daily lives. However, excess usage or aberrant accumulation of ClO- leads to tissue damage or some diseases and even cancer. Therefore, it is necessary to develop a fluorescent probe that specifically identifies ClO- . In this article, we synthesized a deep-red xanthene-based fluorescent probe (XA-CN). The strong electron deficient group dicyano endows the probe XA-CN deep-red fluorescent emission with high solubility, selectivity and sensitivity for ClO- detection. Studies showed that the probe demonstrated turn-off fluorescence (643 nm) at the presence of ClO- in dimethylsulfoxide/phosphate-buffered saline 1:1 (pH 9) solution with a limit of detection of 1.64 µM. Detection mechanism investigation revealed that the electron deficient group -CN and the hydroxyl group was oxidized into aldehyde or carbonyl groups at the presence of ClO- , resulting ultraviolet-visible absorption of the probe blue shifted and turned-off fluorescence. Furthermore, XA-CN was successfully used for the detection of ClO- in tap water samples.

Synthesis of carbazole-based dendritic conjugated polymer: a dual channel optical probe for the detection of I- and Hg2.

A new type of carbazole-based blue-emitting dendritic conjugated polymer, poly[(9,9-dioctyl)-2,7-fluorene-co-4,4',4"-triphenylamine-co-9-(4-(9H-carbazol-9-yl)butyl)-3,6-carbazole](P), was successfully synthesized by Suzuki coupling reaction. Chemical structures of monomers and polymer were verified by FI-IR and 1HNMR characterizations. We found that polymer showed a special selectivity and high sensitivity for I-. With the addition of I-, the fluorescent polymer solution was obviously quenched. The polymer showed a special detection effect on I-. However, the fluorescent polymer was obviously restored when Hg2+ was added to the P/I- system due to the large complexation between I- and Hg2+. The anti-interference experiments of probe P/I- showed that other background cations have a slight influence on detecting Hg2+, and the calculated detection limit of Hg2+ reached 9.7 × 10-8 M, which could be a potential application for a two-channel cyclic detection of I- and Hg2+. Additionally, it was found that the theoretical values were in agreement with the experimental data.

Highly Efficient Fluorescent Organic Light-Emitting Devices Using a Luminescent Radical as the Sensitizer.

In traditional fluorescent organic light-emitting diodes (OLEDs), the upper limit of internal quantum efficiency (IQE) is only 25% because 75% of triplet excitons created on the fluorescent dyes are nonluminous. Here luminescent radicals are proposed as the sensitizer. Under ideal conditions, electrons and holes first recombine on the sensitizer molecule to create doublet excitons, then through energy transfer to generate singlet excitons on the fluorescent dye, and, finally, via radiative decay to emit light. The upper limit of IQE can theoretically reach 100%. As an example, the maximum external quantum efficiency (EQE) of a fluorescent OLED sensitized by a luminescent radical, TTM-1Cz, has reached 8.1%, which is much higher than the upper limit of EQE of traditional fluorescent OLEDs. Our results suggest a new route to realize highly efficient fluorescent OLEDs.

Radical-Based Organic Light-Emitting Diodes with Maximum External Quantum Efficiency of 10.6.

A new luminescent radical, tris-2,4,6-trichlorophenylmethyl-1,5-diazarcarbazole (TTM-DACz), was synthesized and characterized. The photoluminescence quantum yield of TTM-DACz in solid 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene matrix film (5 wt %) is as high as 57.0%. Organic light-emitting diodes (OLEDs) employing TTM-DACz as the emitter were fabricated. By rational design of the device structure and host-guest doping system, external quantum efficiency (EQE) of up to 10.6% of the optimized device with a red CIE chromaticity of (0.62, 0.36) was obtained, which is among the highest values for red OLEDs using nonphosphorescent materials as the emitters. This work will accelerate the development of luminescent radical materials for high-performance OLEDs.

Doublet-Triplet Energy Transfer-Dominated Photon Upconversion.

Stable luminescent π-radicals with doublet emission have aroused a growing interest for functional molecular materials. We have demonstrated a neutral π-radical dye (4-N-carbazolyl-2,6-dichlorophenyl)bis(2,4,6-trichlorophenyl)-methyl (TTM-1Cz) with remarkable doublet emission, which could be used as triplet sensitizer to initiate the photophysical process of triplet-triplet annihilation photon upconversion (TTA-UC). Dexter-like excited doublet-triplet energy transfer (DTET) was confirmed by theoretical calculation. With the same sensitizer, a mixed solution of TTM-1Cz and aromatic emitters could upconvert red light (λ = 635 nm) to blue or cyan light. An anti-Stokes energy shift as large as 0.92 eV was observed from red to blue light upconversion. This finding of DTET phenomena offers a new kind of triplet sensitizer for TTA-UC.

Up to 100% Formation Ratio of Doublet Exciton in Deep-Red Organic Light-Emitting Diodes Based on Neutral π-Radical.

In a neutral π-radical-based organic light-emitting diode (OLED), although the emission comes from the doublet excitons and their transition to the ground state is spin-allowed, the upper limit of internal quantum efficiency (IQE) is not clear, 50% or 100%? In this work, the deep-red OLEDs based on a neutral π-radical were fabricated. Up to 100% doublet exciton formation ratio was obtained through rational designing device structure and host-guest doping system. This indicates the IQE of neutral π-radical-based OLEDs will reach 100% if the nonradiative pathways of radicals can be suppressed. The maximum external quantum efficiency of the optimized device is as high as 4.3%, which is among the highest values of deep-red/near-infrared OLEDs with nonphosphorescent materials as emitters. Our results also indicate that using partially reduced radical mixture as emitter may be a way to solve aggregation-caused quenching in radical-based OLEDs.

Triplet-Polaron-Interaction-Induced Upconversion from Triplet to Singlet: a Possible Way to Obtain Highly Efficient OLEDs.

Two D-A-type molecules, 4-N-[4-(9-phenylcarbazole)]-3,5-bis(4-diphenylamine)phenyl-4H-1,2,4-triazole and 4,4'-(9-(4-(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)phenyl)-9H-carbazole-3,6-diyl) bis-(N,N-diphenylaniline), are designed and synthesized. Organic lightemitting diodes based on them exhibit deep-blue emission and the singlet formation ratios are higher than the simple spin-statistics of 25%. A triplet-polaroninteraction-induced upconversion from triplet to singlet through a one-electron transfer mechanism is proposed, and is proven by magnetocurrent measurement and quantum-chemistry computation.

Organic Light-Emitting Diodes Using a Neutral π†Radical as Emitter: The Emission from a Doublet.

Triplet harvesting is a main challenge in organic light-emitting devices (OLEDs), because the radiative decay of the triplet is spin-forbidden. Here, we propose a new kind of OLED, in which an organic open-shell molecule, (4-N-carbazolyl-2,6-dichlorophenyl)bis(2,4,6-trichlorophenyl)methyl (TTM-1Cz) radical, is used as an emitter, to circumvent the transition problem of triplet. For TTM-1Cz, there is only one unpaired electron in the highest singly occupied molecular orbital (SOMO). When this electron is excited to the lowest singly unoccupied molecular orbital (SUMO), the SOMO is empty. Thus, transition back of the excited electron to the SOMO is totally spin-allowed. Spectral analysis showed that electroluminescence of the OLED originated from the electron transition between SUMO and SOMO. The magneto-electroluminescence measurements revealed that the spin configuration of the excited state of TTM-1Cz is a doublet. Our results pave a new way to obtain 100% internal quantum efficiency of OLEDs.