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Electric field induced fluorescence modulation of single molecules in PMMA based on electron transfer.

Chen R, Gao Y, Zhang G, Wu R, Xiao L, Jia S - Int J Mol Sci (2012)

Bottom Line: We present a method to modulate the fluorescence of non-polar single squaraine-derived rotaxanes molecules embedded in a polar poly(methyl methacrylate) (PMMA) matrix under an external electric field.The electron transfer between single molecules and the electron acceptors in a PMMA matrix contributes to the diverse responses of fluorescence intensities to the electric field.The observed instantaneous and non-instantaneous electric field dependence of single-molecule fluorescence reflects the redistribution of electron acceptors in PMMA induced by electronic polarization and orientation polarization of polar polymer chains in an electric field.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Quantum Optics and Quantum Optics Devices, Laser Spectroscopy Laboratory, Shanxi University, Taiyuan 030006, China; E-Mails: chenry421@163.com (R.C.); ggnnool@163.com (Y.G.); gfzhang@mail.sxu.cn (G.Z.); Wurx464628021@163.com (R.W.); tjia@sxu.edu.cn (S.J.).

ABSTRACT
We present a method to modulate the fluorescence of non-polar single squaraine-derived rotaxanes molecules embedded in a polar poly(methyl methacrylate) (PMMA) matrix under an external electric field. The electron transfer between single molecules and the electron acceptors in a PMMA matrix contributes to the diverse responses of fluorescence intensities to the electric field. The observed instantaneous and non-instantaneous electric field dependence of single-molecule fluorescence reflects the redistribution of electron acceptors in PMMA induced by electronic polarization and orientation polarization of polar polymer chains in an electric field.

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(a) and (b) are the chemical structures of squaraine-derived rotaxanes (SR) dye molecule and PMMA polymer chain, respectively; (c) Schematic of experimental setup for single molecule detection based on a confocal microscope. The enlarged part shows the pattern of electrodes; (d) Shows the confocal scanned fluorescence image (10 × 10 μm2) of SR molecules sandwiched PMMA film.
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f5-ijms-13-11130: (a) and (b) are the chemical structures of squaraine-derived rotaxanes (SR) dye molecule and PMMA polymer chain, respectively; (c) Schematic of experimental setup for single molecule detection based on a confocal microscope. The enlarged part shows the pattern of electrodes; (d) Shows the confocal scanned fluorescence image (10 × 10 μm2) of SR molecules sandwiched PMMA film.

Mentions: Squaraine-derived rotaxane dye molecules [31], whose maximum excitation wavelength is 650 nm and maximum fluorescence emission wavelength is 678 nm (1.82 eV), was purchased from Molecular Targeting Technologies Inc. (West Chester, PA, USA) The chemical structure of SR is shown in Figure 5a. PMMA (MW = 15,000, Tg = 82 °C) was purchased from Aldrich. The chemical structure of the PMMA chain is shown in Figure 5b. The PMMA-toluene co-solution (20 g L−1 PMMA) was first spin-coated at 3000 rpm onto a glass cover slip on which aluminum electrodes were fabricated. The aluminum electrodes with a thickness of 1.5 μm and a gap of 10 μm between two adjacent arms were prepared using aluminum alloy e-beam evaporator and standard optical lithography. The sample was prepared by spin-coating 20 μL water solution containing SR molecules at a concentration of 10−10–10−9 M into the electrode gaps. A PMMA film was further spin-coated onto the sample. The sandwich-like sample was carefully prepared to isolate the molecules from the electrodes to avoid charge injection and to prevent oxygen-induced fast photobleaching. The sample was heated under vacuum to 373 K for 3 h then held overnight under vacuum at room temperature to remove the remaining solvent and relax stresses induced by the spin-coating process. The resulting thickness of the sample films amounts to about 200 nm. The upper right image in Figure 5c shows the pattern of electrodes. Square alternating voltage was applied to two neighboring arms of aluminum electrodes at a frequency of 0.1 Hz, which yielded a parallel EF between the two neighboring arms of electrodes. The single molecules were dispersed in the electrode gaps with random directions with respect to the parallel EF.


Electric field induced fluorescence modulation of single molecules in PMMA based on electron transfer.

Chen R, Gao Y, Zhang G, Wu R, Xiao L, Jia S - Int J Mol Sci (2012)

(a) and (b) are the chemical structures of squaraine-derived rotaxanes (SR) dye molecule and PMMA polymer chain, respectively; (c) Schematic of experimental setup for single molecule detection based on a confocal microscope. The enlarged part shows the pattern of electrodes; (d) Shows the confocal scanned fluorescence image (10 × 10 μm2) of SR molecules sandwiched PMMA film.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC3472734&req=5

f5-ijms-13-11130: (a) and (b) are the chemical structures of squaraine-derived rotaxanes (SR) dye molecule and PMMA polymer chain, respectively; (c) Schematic of experimental setup for single molecule detection based on a confocal microscope. The enlarged part shows the pattern of electrodes; (d) Shows the confocal scanned fluorescence image (10 × 10 μm2) of SR molecules sandwiched PMMA film.
Mentions: Squaraine-derived rotaxane dye molecules [31], whose maximum excitation wavelength is 650 nm and maximum fluorescence emission wavelength is 678 nm (1.82 eV), was purchased from Molecular Targeting Technologies Inc. (West Chester, PA, USA) The chemical structure of SR is shown in Figure 5a. PMMA (MW = 15,000, Tg = 82 °C) was purchased from Aldrich. The chemical structure of the PMMA chain is shown in Figure 5b. The PMMA-toluene co-solution (20 g L−1 PMMA) was first spin-coated at 3000 rpm onto a glass cover slip on which aluminum electrodes were fabricated. The aluminum electrodes with a thickness of 1.5 μm and a gap of 10 μm between two adjacent arms were prepared using aluminum alloy e-beam evaporator and standard optical lithography. The sample was prepared by spin-coating 20 μL water solution containing SR molecules at a concentration of 10−10–10−9 M into the electrode gaps. A PMMA film was further spin-coated onto the sample. The sandwich-like sample was carefully prepared to isolate the molecules from the electrodes to avoid charge injection and to prevent oxygen-induced fast photobleaching. The sample was heated under vacuum to 373 K for 3 h then held overnight under vacuum at room temperature to remove the remaining solvent and relax stresses induced by the spin-coating process. The resulting thickness of the sample films amounts to about 200 nm. The upper right image in Figure 5c shows the pattern of electrodes. Square alternating voltage was applied to two neighboring arms of aluminum electrodes at a frequency of 0.1 Hz, which yielded a parallel EF between the two neighboring arms of electrodes. The single molecules were dispersed in the electrode gaps with random directions with respect to the parallel EF.

Bottom Line: We present a method to modulate the fluorescence of non-polar single squaraine-derived rotaxanes molecules embedded in a polar poly(methyl methacrylate) (PMMA) matrix under an external electric field.The electron transfer between single molecules and the electron acceptors in a PMMA matrix contributes to the diverse responses of fluorescence intensities to the electric field.The observed instantaneous and non-instantaneous electric field dependence of single-molecule fluorescence reflects the redistribution of electron acceptors in PMMA induced by electronic polarization and orientation polarization of polar polymer chains in an electric field.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Quantum Optics and Quantum Optics Devices, Laser Spectroscopy Laboratory, Shanxi University, Taiyuan 030006, China; E-Mails: chenry421@163.com (R.C.); ggnnool@163.com (Y.G.); gfzhang@mail.sxu.cn (G.Z.); Wurx464628021@163.com (R.W.); tjia@sxu.edu.cn (S.J.).

ABSTRACT
We present a method to modulate the fluorescence of non-polar single squaraine-derived rotaxanes molecules embedded in a polar poly(methyl methacrylate) (PMMA) matrix under an external electric field. The electron transfer between single molecules and the electron acceptors in a PMMA matrix contributes to the diverse responses of fluorescence intensities to the electric field. The observed instantaneous and non-instantaneous electric field dependence of single-molecule fluorescence reflects the redistribution of electron acceptors in PMMA induced by electronic polarization and orientation polarization of polar polymer chains in an electric field.

Show MeSH
Related in: MedlinePlus