Department of Chemistry, William Mong Institute of Nano Science and Technology, Bioengineering Graduate Program, The Hong Kong University of Science & Technology (HKUST), Clear Water Bay, Kowloon, Hong Kong, China, and Department of Polymer Science and Engineering, Key Laboratory of Macromolecular Synthesis and Functionalization of the Ministry of Education, Institute of Biomedical Macromolecules, Zhejiang University, Hangzhou 310027, China

Acetylenic polymers: syntheses, structures, and functions.

It has been difficult to decipher the mechanistic issue whether E/Z isomerization is involved in the aggregation-induced emission (AIE) process of a tetraphenylethene (TPE) derivative, due to the difficulty in the synthesis of its pure E and Z conformers. In this work, pure stereoisomers of a TPE derivative named 1,2-bis{4-[1-(6-phenoxyhexyl)-4-(1,2,3-triazol)yl]phenyl}-1,2-diphenylethene (BPHTATPE) are successfully synthesized. Both isomers show remarkable AIE effect (αAIE ≥ 322) and high fluorescence quantum yield in the solid state (ΦF 100%). The conformers readily undergo E/Z isomerization upon exposure to a powerful UV light and treatment at a high temperature (>200 °C). Such conformational change, however, is not observed under normal fluorescence spectrum measurement conditions, excluding the involvement of the E/Z isomerization in the AIE process of the TPE-based luminogen. The molecules of (E)-BPHTATPE self-organize into ordered one-dimensional nanostructures such as microfibers and nanorods that...

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Click Synthesis, Aggregation-Induced Emission, E/Z Isomerization, Self-Organization, and Multiple Chromisms of Pure Stereoisomers of a Tetraphenylethene-Cored Luminogen

Metallic nanostructures now play an important role in many applications. In particular, for the emerging fields of plasmonics and nanophotonics, the ability to engineer metals on nanometric scales allows the development of new devices and the study of exciting physics. This review focuses on top-down nanofabrication techniques for engineering metallic nanostructures, along with computational and experimental characterization techniques. A variety of current and emerging applications are also covered.

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Engineering metallic nanostructures for plasmonics and nanophotonics

There is a great demand for long-term cellular tracers because of their great importance in monitoring biological processes, pathological pathways, therapeutic effects, etc. Herein we report a new type of fluorescence “turn-on” probe for tracing live cells over a long period of time. We synthesized the fluorogenic probe by attaching a large number of tetraphenylethene (TPE) labels to a chitosan (CS) chain. The resultant TPE–CS bioconjugate shows a unique aggregation-induced emission (AIE) behavior. It is nonfluorescent when dissolved but becomes highly emissive when its molecules are aggregated. The AIE aggregates can be readily internalized by HeLa cells. The cellular staining by the TPE–CS aggregates is so indelible that it enables cell tracing for as long as 15 passages. The internalized AIE aggregates are kept inside the cellular compartments and do not contaminate other cell lines in the coculture systems, permitting the differentiation of specific cancerous cells from normal healthy cells.

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Long-term fluorescent cellular tracing by the aggregates of AIE bioconjugates.

Whereas chain aggregation commonly quenches light emission of conjugated polymers, we here report a phenomenon of aggregation-induced emission enhancement (AIEE): luminescence of polyacetylenes is dramatically boosted by aggregate formation. Upon photoexcitation, poly(1-phenyl-1-alkyne)s and poly(diphenylacetylene)s emit blue and green lights, respectively, in dilute THF solutions. The polymers become more emissive when their chains are induced to aggregate by adding water into their THF solutions. The polymer emissions are also enhanced by increasing concentration and decreasing temperature. Lifetime measurements reveal that the excited species of the polymers become longer-lived in the aggregates. Conformational simulations suggest that the polymer chains contain n = 3 repeat units that facilitate the formation of intramolecular excimers. The AIEE effects of the polymers are rationalized to be caused by the restrictions of their intramolecular rotations by the aggregate formation.

Aggregation-Enhanced Emissions of Intramolecular Excimers in Disubstituted Polyacetylenes

Very recently, in a short letter [Appl Phys Lett 91, 111111 (2007)], we outlined some important results of electromagnetic transmission in dual-metallic grating structures composed of two identical single-metallic gratings with periodic subwavelength slit arrays Here we describe and explain our theoretical study on the propagation property of the electromagnetic radiation in such structures in detail The results manifest that the longitudinal interval and lateral displacement between the two single-metallic gratings strongly influence the electromagnetic transmission behavior in the dual-metallic grating structures We discover some interesting phenomena such as the frequency shift and splitting of the high transmission peak, and the transmission suppression over a broad frequency region We reveal that the coupling between the two single-metallic gratings is responsible for those phenomena In addition, the case of oblique incidence is also explored

Physical mechanism of extraordinary electromagnetic transmission in dual-metallic grating structures

Electromagnetic (EM) transmission through dual-metallic grating (DMG) structures composed of slits arrays, with the longitudinal interval G and the lateral displacement L, is investigated by using the finite-difference time-domain method. The results show that the EM transmission property can be controlled by changing G or/and L, such as tunable wavelength of high transmission, changeable transmittance for a special wavelength, and suppressed EM transmission over a broad spectral range. The DMG structures have potential applications in the future photonics. In addition, some advantages of DMGs with respect to the single-metallic gratings are also discussed.

Controllable electromagnetic transmission based on dual-metallic grating structures composed of subwavelength slits

We focus on the lateral shift for an electromagnetic wave reflected from a weakly absorbing double negative medium (DNM). A large lateral shift near the pseudo-Brewster angle is found, which may be negative or positive. We give an analytic expression for such a kind of lateral shift, from which the critical transition point for sign-changing of the lateral shift can be easily obtained. Theoretical analysis shows that the absorption of DNM, even though very weak, plays an important role in determining the lateral shift. As evidences, we calculate the lateral shift by means of the momentum method and perform the finite-difference time-domain (FDTD) simulations. We find that the results of our theoretical analysis are reliable.

Large lateral shift near pseudo-Brewster angle on reflection from a weakly absorbing double negative medium.

The invention discloses an adjustable electromagnetic wave transmitting frame, which is based on sub-wavelength metal double gratings and comprises two single layer sub-wavelength metal gratings, wherein the two single layer sub-wavelength metal gratings are arranged in parallel, distance and transverse displacement of the gratings can be adjusted. The frame is based on a waveguide module of metal surface plasmons, incident electromagnetic waves which are adjustable are p-polarizations, a period of a grating is less than wave length of the electromagnetic waves, and a slot width is less than half-wave length of a electromagnetic wave. Coupling effects which are through evanescent field between the gratings can be adjusted through changing the distance G and the transverse displacement L which are between neighboring metal gratings, thereby electromagnetic transmitting property of a component can be changed, and the purpose for adjusting electromagnetic wave transmitting spectra can be achieved.

Qi-Yang Wu

Papers

Physical mechanism of extraordinary electromagnetic transmission in dual-metallic grating structures

Controllable electromagnetic transmission based on dual-metallic grating structures composed of subwavelength slits

Large lateral shift near pseudo-Brewster angle on reflection from a weakly absorbing double negative medium.

Controllable electromagnetic wave transmittance structure based on sub-wave length metal double gratings and its preparation method