Liqi Shi

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.

Conjugated polymer-titania nanoparticle hybrid films: random lasing action and ultrasensitive detection of explosive vapors.

We have first demonstrated that a random laser action generated by a hybrid film composed of a semiconducting organic polymer (SOP) and TiO(2) nanoparticles can be used to detect 2,4,6-trinitrotoluene (TNT) vapors. The hybrid film was fabricated by spin-casting SOP solution dispersed with nanosized TiO(2) particles on quartz glass. The SOP in the hybrid film functioned as both the gain medium and the sensory transducer. A random lasing action was observed with a certain pump power when the size (diameter of 50 nm) and concentration (8.9 x 10(12)/cm(3)) of TiO(2) nanoparticles were optimized. Measurements of fluorescence quenching behavior of the hybrid film in TNT vapor atmosphere (10 ppb) showed that attenuated lasing in optically pumped hybrid film displayed a sensitivity to vapors of explosives more than 20 times higher than was observed from spontaneous emission. This phenomenon has been explained with the four-level laser model. Since the sensory transducer used in the hybrid polymer/nanoparticles system could be replaced by other functional materials, the concept developed could be extended to more general domains of chemical or environment detection.

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.

Turn-on lasing sensory mechanism for vapor detection of amines with metallophenylporphrin doped polyfluorene

We report here a lasing “turn-on” sensory mechanism for highly sensitive vapor detection of amines, utilizing a polyfluorene/palladium tetraphenylporphyrin (PFO/PdTPP) composite film as the sensing medium. A rational ratio of PdTPP could effectively quench the fluorescence of PFO, and the fluorescence recovery occurs after electron donating amine binds to PdTPP, which resulting in a “turn-on” lasing action under optical pump. The lasing “turn-on” action shows sensitivity more than 5 times higher compared with the spontaneous emission (fluorescence) detection. Various amines have different binding intensity with PdTPP as well as diverse fluorescence recovery features brought on the distinction of lasing thresholds and the selectivity of sensing amines.

Fluorene-thiophene-based thin-film fluorescent chemosensor for methamphetamine vapor

We here report a new “turn-on” sensory mechanism for vapor sensing in solid-state based on binding-induced weakening of internal heavy-atom effect. Spin-coating films of 9, 9-diocylfluorene-2, 7-bisthiphene 1 and poly [(9, 9-diocylfuorenyl-2, 7-diyl)-alt (3-hexylthiophene-2, 5-diyl)] 2 were obtained and characterized by absorption and fluorescence spectra. The vapor sensing behaviors of the films were investigated with respect to the amines such as n-propylamine, aniline, benzylamine, p-toluidine, diisopropylanmine and methylamphetamine at room temperature. The result indicated that the films exhibited rapid and selective “turn-on” fluorescent response to methylamphetamine vapor.