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(a) Schematic of the experimental setup. SS: piezo-scan stage; DM: dichroic mirror; E: emission filter; N: notch filter; P: pinhole; SPCM: single photon counting module; H: half-wave plate; and Q: quarter-wave plate. Solid and dashed lines indicate the laser and fluorescence, respectively. The upper right exemplifies the pattern of electrodes. (b) and (c) are the chemical structures of squaraine-derived rotaxane (SR) dye molecule and PMMA chain, respectively.
Schematic of electron transfer of single molecule in PMMA host matrix. The acceptor sites surrounding the impurity molecule provide a potential valley with a barrier higher than the excited energy level of molecule. kf and kb represent the forward and backward electron transfer rate between the photoexcited molecule and potential valley, respectively. The interaction between the molecular energies and potential valley can be detuned by electric field, and then change the electron transfer rates.
(a) Different types of fluorescence response of single SR molecules in PMMA matrix as a function of time together with the applied EF of 0.75 MV cm−1: EF-induced quenching, EF-induced enhancement, and no response, respectively. The binning time is 10 ms. (b) Distribution of EF-induced fluorescence modulation depth for 87 single SR molecules in PMMA at EF of 0.75 MV cm−1.
(a) Photoluminescence trace of individual SR molecule at an EF of 0.75 MV cm−1. The bias resulted in a quenching in the fluorescence and a slow decay time. While turning off the bias, a faster recovery of the fluorescence was found. (b) and (c) The exponential fits of quenching and recovery time constants of same molecule, respectively, averaged over 7 complete cycles. (d) Distribution of the transient response for field induced fluorescence quenching molecules and field induced fluorescence enhancement molecules under two different EFs, with horizontal axis the EF-induced response time of fluorescence and vertical axis the recovery time of fluorescence when the EF is turned off, respectively.
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