Defeng Zhu

High performance aniline vapor detection based on multi-branched fluorescent triphenylamine-benzothiadiazole derivatives: branch effect and aggregation control of the sensing performance

A series of benzothiadiazole-pyridine branched triphenylamine derivatives TPA1BP, TPA2BP and TPA3BP have been designed and synthesized to sense aniline vapor with distinguished sensitivity, selectivity and repeatability via photoinduced electron transfer (PET). Suitable energy levels ensure the high selectivity to aniline for all three sensory materials. However, the aggregations of the three materials in the film state on a quartz substrate increase along with the branches, which highly deteriorate the sensing performance for less efficient fluorescence, lower contact area and inferior vapor penetration. The oriented ZnO nanorod array is introduced as the substrate to eliminate the aggregation and enhance the sensing performance, because of its high surface-to-volume ratio and 3D structure. Therefore, the cooperative effect that the sensing performance of TPAnBP increases with the number of branches could be observed; fluorescence intensities of the films on the nano-substrate are 34%, 45% and 54% quenched for TPA1BP, TPA2BP and TPA3BP, respectively, after exposure to 300 ppm aniline vapor for less than 5 s. Moreover, the fluorescences of all three sensory materials are almost 100% recovered by eluting with fresh air for 20 s and could be reused immediately. The detection limits are predicted to be 1 ppm for TPA1BP, 100 ppb for TPA2BP and 1 ppb for TPA3BP according to the fitted plot, demonstrating a significant cooperative effect of the molecular branches.

Sensitivity gains in chemosensing by optical and structural modulation of ordered assembly arrays of ZnO nanorods.

Nanomaterials and -structures have attracted much attention owing to their applications to ultrasensitive nanodevices. In this work, ordered assembly arrays of ZnO nanorods have been hydrothermally fabricated and used as optical substrates of fluorescence sensors for toxic vapors. The unique fastigiate nanorod assembly combines merits of single fibers and clusters, possessing identical orientation, large surface-to-volume ratio, evanescent transmission, and evanescent coupling. As coated on the assembly arrays, different sensing materials all generated amplified spontaneous emission (ASE) action such that the fluorescence intensity of the narrowed spectrum was 52.4-fold enhanced. Results of sensing experiments indicate that sensors based on the assembly arrays displayed 100% elevated normalized quenching rate and several times longer full-load time compared with reference sensors. This work provides a facile method to fabricate secondary structures of 1D rigid material and presents a new way to design highly sensitive optic sensors. Furthermore, evanescent excitation caused ASE action of fluorescent organics, and the correlative sensitivity gain is of interest in both theoretical research and the applications field.

Concise and Efficient Fluorescent Probe via an Intromolecular Charge Transfer for the Chemical Warfare Agent Mimic Diethylchlorophosphate Vapor Detection

Sarin, used as chemical warfare agents (CWAs) for terrorist attacks, can induce a number of virulent effects. Therefore, countermeasures which could realize robust and convenient detection of sarin are in exigent need. A concise charge-transfer colorimetric and fluorescent probe (4-(6-(tert-butyl)pyridine-2-yl)-N,N-diphenylaniline, TBPY-TPA) that could be capable of real-time and on-site monitoring of DCP vapor was reported in this contribution. Upon contact with DCP, the emission band red-shifted from 410 to 522 nm upon exposure to DCP vapor. And the quenching rate of TBPY-TPA reached up to 98% within 25 s. Chemical substances such as acetic acid (HAc), dimethyl methylphosphonate (DMMP), pinacolyl methylphosphonate (PAMP), and triethyl phosphate (TEP) do not interfere with the detection. A detection limit for DCP down to 2.6 ppb level is remarkably achieved which is below the Immediately Dangerous to Life or Health concentration. NMR data suggested that a transformation of the pyridine group into pyridinium salt via a cascade reaction is responsible for the sensing process which induced the dramatic fluorescent red shift. All of these data suggest TBPY-TPA is a promising fluorescent sensor for a rapid, simple, and low-cost method for DCP detection, which could be easy to prepare as a portable chemosensor kit for its practical application in real-time and on-site monitoring.

A BODIPY dye as a reactive chromophoric/fluorogenic probe for selective and quick detection of vapors of secondary amines

A new reaction based fluorescence turn-off strategy for detection of secondary amines was developed. The probe shows fast response and high selectivity to secondary amines in solution/film at sub-ppm levels through chromogenic and fluorescent dual-mode signal changes.

Poly(phenylene ethynylene)-coated aligned ZnO nanorod arrays for 2,4,6-trinitrotoluene detection

The structure of ZnO nanorods coated with fluorescent polymer poly(phenylene ethynylene) (PPE) have been fabricated for 2,4,6-trinitrotoluene (TNT) detection. In this structure, hydrothermally synthesized crystalline ZnO nanorod arrays were used as waveguides and supporting materials for the TNT sensitive polymer, PPE. The evanescent-wave guiding property of the ZnO nanorod waveguide considerably increased fluorescence intensity. The space between the adjacent nanorods and the larger surface-to-volume ratio of the nanorods enhanced the fluorescence response (quenching) to TNT vapor. This work will contribute to design of combining ZnO nanorod arrays with a functional polymer for sensor applications.

Borate ester endcapped fluorescent hyperbranched conjugated polymer for trace peroxide explosive vapor detection

The vapor of peroxide explosives (PEs) is difficult to detect using fluorescent probes because PEs are not typical quenching agents, not having nitro groups or aromatic units that can easily interact with electron-rich probes. Three borate ester endcapped pyrenyl–fluorene copolymers were reported for the detection of PEs, including a hyperbranched polymer (S1) and two linear polymers with borate esters on fluorenyl (S2) or pyrenyl (S3) units. It was found that the hyperbranched polymer S1 has greater steric hindrance, more external borate ester groups, higher HOMO level and higher fluorescence quantum yield, which give it higher sensitivity to H2O2 vapor than S2 and S3. To further amplify the sensing performance toward H2O2 vapor, a polymer/ZnO nanorod array composite was used, exploiting the catalytic ability and high area to volume ratio of the ZnO nanorod array. The fluorescence of the S1 film is quenched by ∼60% and ∼30% under saturated vapor of H2O2 and TATP, respectively, for 300 s at room temperature, and the detection limit for H2O2 is estimated to be 1.6 ppb. These results reveal that the S1/ZnO nanorod array composite is very promising for the preparation of a highly sensitive fluorescence device for detecting the vapor of peroxide explosives.

Reversible and “fingerprint” fluorescence differentiation of organic amine vapours using a single conjugated polymer probe

An ultrasensitive and reversible “fingerprint” fluorescent probe has been developed by embedding multiple reactive groups onto one conjugated polymer backbone. The probe can be used for the simultaneous detection of primary aliphatic amines, secondary aliphatic amines, aromatic amines and their mixtures.

Femtogram level detection of nitrate ester explosives via an 8-pyrenyl-substituted fluorene dimer bridged by a 1,6-hexanyl unit.

Compared with nitroaromatic explosives detection, nitrate esters are far from wide attention possibly because of their shortage of aromatic ring and difficulty in being detected. Three fluorescent chemical probes for trace nitrate ester detection: an intramolecular dimer (P3) of 8-pyrenyl-substituted fluorenes bridged by a 1,6-hexanyl unit as well as its counterparts 2PR-F (P1) and 2PR-Cz (P2) has been synthesized and characterized. Their chemical structures and photophysical and electrochemical properties show that the dimer P3 film has a higher molar extinction coefficient, larger steric hindrance, higher area-to-volume ratio, and matching energy level with nitrate ester explosives, which contributes to higher sensitivity and moderate selectivity for sensing of nitrate ester explosives such as nitroglycerin (NG). The fluorescence of the P3 film is rapidly about 90% quenched upon exposure to a saturated vapor of NG for 50 s and almost 100% quenched for 300 s at room temperature due to photoinduced electron transfer between the probe and analyte. In addition, a very sensitive, rapid, simple, and low-cost surface-sensing method by disposable filter-paper-based test strips is demonstrated. The contact-mode approach exhibits a detection limit as low as 0.5 fg/cm(2) for NG. These results reveal that the multiple-pyrenyl-unit-substituted fluorene dimer P3 is suitable for preparing a highly sensitive and efficient thin-film device for detecting nitrate esters.

Schiff Base Substituent-Triggered Efficient Deboration Reaction and Its Application in Highly Sensitive Hydrogen Peroxide Vapor Detection.

The organic thin-film fluorescence probe, with the advantages of not polluting the analyte and fast response, has attracted much attention in explosive detection. Different with nitro explosives, the peroxide-based explosives are hardly to be detected because of their poor ultraviolet absorption and lack of an aromatic ring. As the signature compound of peroxide-based explosives, H2O2 vapor detection became more and more important. Boron ester or acid is considered to be a suitable functional group for the detection of hydrogen peroxide due to its reliable reactive activity. Its only drawback lies on its slow degradation velocity. In this work, we try to introduce some functional group to make the boron ester to be easily oxidized by H2O2. Herein, 4-(phenyl(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)amino)benzaldehyde (OTB) was synthesized and its imine derivatives, OTBXAs, were easily obtained just by putting OTB films in different primary amines vapors. OTBXAs show fast deboronation velocity in H2O2 vapor compared with OTB. The complete reaction time of (E)-N-phenyl-4-((propylimino)methyl)-N-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)aniline (OTBPA) was even shortened 40 times with a response time of seconds. The detection limit for H2O2 vapor was as low as 4.1 parts per trillion (ppt). Further study showed that it is a general approach to enhance the sensing performance of borate to hydrogen peroxide (H2O2) vapor by introducing an imine into an aromatic borate molecule via a solid/vapor reaction.

Highly efficient nitrate ester explosive vapor probe based on multiple triphenylaminopyrenyl-substituted POSS

Compared with nitroaromatic explosive detection, nitrate ester explosive detection has not received considerable attention possibly due to the absence of an aromatic ring and their difficulty in being detected. An eight triphenylamino-pyrenyl substituted POSS (P8PT) was designed as a sensory material. POSS was chosen as the skeleton due to its nano structure, multiple reactive sites, structural similarity with nitrate esters and high thermal stability, which will contribute to large surface area induced high sensitivity, tunable sensory units number, stronger interaction force with nitrate esters and high stability. For comparison, triphenylamino-pyrene (Py-TPA) (without POSS), one and three Py-TPA substituted POSS were also synthesized and characterized. Their chemical structures, photophysical and electrochemical properties show that P8PT has a 3-D symmetrical spatial conformation, higher molar extinction coefficient, higher area-to-volume ratio, multiple exciton transfer path, and matched energy level with nitrate ester explosives, which will all contribute to highly efficient sensing performance and efficient selectivity for the detection of nitrate ester explosives such as nitroglycerin (NG). The fluorescence of the P8PT film is 63% quenched upon exposure to a saturated vapor of NG for 50 s and 92% quenched for 300 s at room temperature due to photoinduced electron transfer between the probe and NG. These results reveal that P8PT is suitable for preparing a highly sensitive and efficient thin-film device for detecting nitrate esters.