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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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Related in: MedlinePlus

HOMO/LUMO energy level scheme of SR molecule (adapted from [31]) as well as electron acceptor states in PMMA (adapted from [32]) with respect to the vacuum level.
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f4-ijms-13-11130: HOMO/LUMO energy level scheme of SR molecule (adapted from [31]) as well as electron acceptor states in PMMA (adapted from [32]) with respect to the vacuum level.

Mentions: After a single molecule is photoexcited, the resulting first excited state may relax via several competing pathways: radiative or non-radiative decay to the ground state, formation of a long-living triplet state or charge separation. It has been proposed in numerous studies that charge transfer is a dominant fluorescence-quenching pathway, which could be controlled by external EF. Therefore, the fluorescence efficiency may be reduced or enhanced by EF-induced modulation of the charge transfer rate. The modulation effect in Figure 1 can be properly explained by diminishment or enhancement of the fluorescence-quenching pathway induced by external EF. It has been proposed that the carbonyls in the PMMA ester groups can serve as electron acceptors surrounding single molecules [10]. The acceptors are well known to play an important role in polymers in contact charging or contact electrification experiments where a charge flow from the metal into the polymer was observed. Figure 4 shows the HOMO/LUMO levels of an SR molecule adapted from ref. [31] and the energies of electron acceptor states in PMMA determined by contact charging experiments [32]. Based on the energetic considerations, forward and backward electron transfer may happen between single molecules and acceptors in the surrounding environment. Excited electrons of single molecules may forward electron transfer to acceptors in the surrounding environment, which will lead to the decrease of the fluorescence quantum yield. Meanwhile, the electrons trapped in acceptors would also back transfer to the single molecule to renew excitation and emission cycles.


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)

HOMO/LUMO energy level scheme of SR molecule (adapted from [31]) as well as electron acceptor states in PMMA (adapted from [32]) with respect to the vacuum level.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4-ijms-13-11130: HOMO/LUMO energy level scheme of SR molecule (adapted from [31]) as well as electron acceptor states in PMMA (adapted from [32]) with respect to the vacuum level.
Mentions: After a single molecule is photoexcited, the resulting first excited state may relax via several competing pathways: radiative or non-radiative decay to the ground state, formation of a long-living triplet state or charge separation. It has been proposed in numerous studies that charge transfer is a dominant fluorescence-quenching pathway, which could be controlled by external EF. Therefore, the fluorescence efficiency may be reduced or enhanced by EF-induced modulation of the charge transfer rate. The modulation effect in Figure 1 can be properly explained by diminishment or enhancement of the fluorescence-quenching pathway induced by external EF. It has been proposed that the carbonyls in the PMMA ester groups can serve as electron acceptors surrounding single molecules [10]. The acceptors are well known to play an important role in polymers in contact charging or contact electrification experiments where a charge flow from the metal into the polymer was observed. Figure 4 shows the HOMO/LUMO levels of an SR molecule adapted from ref. [31] and the energies of electron acceptor states in PMMA determined by contact charging experiments [32]. Based on the energetic considerations, forward and backward electron transfer may happen between single molecules and acceptors in the surrounding environment. Excited electrons of single molecules may forward electron transfer to acceptors in the surrounding environment, which will lead to the decrease of the fluorescence quantum yield. Meanwhile, the electrons trapped in acceptors would also back transfer to the single molecule to renew excitation and emission cycles.

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