Cyclodextrin Nanocavity Caging Effect on Electronic Dephasing

Abstract

The ability to control molecular wavefunctions may lead to novel quantum technologies, such as bond-selective chemistry and quantum computing. [1][2][3] An understanding of the coherent-loss process is essential for the realization of these quantum technologies using quantum-interference (QI) effects in condensed media. Although the overwhelming majority of chemical reactions take place in solution, there have been very few experimental studies on the coherent reaction control of polyatomic molecules in condensed media, because of the rapid decoherence of wavefunctions. These fast quantumphase relaxations are thought to be caused by solute-solvent interactions. [4,5] Thus, an understanding of the roles of solvent molecules in the dephasing mechanism is strongly required. It is noted that the inhibition of dephasing is necessary for the development of coherent control techniques for more general reactions. Therefore, the protection of molecular wavefunctions from the surrounding environment becomes an important issue for the realization of quantum-control techniques in condensed phases. Here, we aimed to protect the quantum phase of a guest molecule by using the size-fit nanospace of a cyclodextrin nanocavity.Cyclodextrins (a-, b-, or g-CD), which are oligosaccharides with hydrophobic interiors and hydrophilic exteriors, are used as nanocavities. The ability of CDs to encapsulate organic and inorganic molecules in aqueous solution has led to intensive studies of their inclusion complexes.[6] We intuitively imagined that the confinement of a guest molecule within the CD nanocavity would reduce perturbations from the surrounding environment, which cause the decoherence. Several studies on CD complexes with aromatic compounds, performed using timeresolved spectroscopy, have been reported. [6][7][8][9][10][11][12][13] To our knowledge, however, no experiments have been reported on CD inclusion to suppress decoherence. As far as we know, this is the first report on the CD encapsulation effect that moderates the decoherence of the molecular wavefunction at room temperature.Herein, we report the moderation of electronic decoherence of perylene in g-CD at room temperature, as measured by an optical-phase-controlled pulse-pair quantum interferometer, [14][15][16][17][18][19][20][21][22][23] combined with spectral lineshape analysis. A method to induce QI of molecular wavefunctions by a pair of phaselocked pulses has been originally developed by Scherer et al. and successfully applied to I 2 molecules in the gas phase. [14] The QI technique was successfully applied to various systems, such as GaAs quantum dots, [15,16] ZnSe films, [17] the Rydberg atom, [18,19] Cl 2 in an Ar matrix, [20] I 2 in the gas phase, [21,22] and a microcrystalline powder of a linked anthracene dimer.[23] Figure 1 shows the steady-state fluorescence and fluorescence-excitation spectra of perylene in both a g-CD aqueous solution and a tetrahydrofuran (THF) solution. Because of the low solubility of perylene in water (ca. 1.6 10 À9 m), [24] we could n...

Fluorophore discrimination by tracing quantum interference in fluorescence microscopy

“…Taking into account the spectral line shape of absorption (which turns out to be a Voigt profile when both the homogeneous contribution with Lorentzian line shape as well as the inhomogeneous contribution with Gaussian line shape are present) and laser pulse (Gaussian profile), the QI signal under periodically phase-modulated pulse-pair excitation has shown to be varied for two different scenarios [13]: (1) if the pulse spectral width is at least an order of magnitude larger than the absorption linewidth, one expects the fringe frequency to be the inverse of the frequency width of the absorption profile and (2) at the other extreme, if a narrow pulse spectrum excites a subpopulation of the broad inhomogeneous absorption line shape, then the temporal fringe oscillations occur at a pulse carrier-wave frequency analogous to ultrafast hole-burning experiments [9,32]. For an intermediate situation (which happens to be the case in our experiment), the QI signal is neither given by the inverse of the spectral width nor follows the optical field oscillations [13,14]; for partial pulse-pair overlapping zone the QI signal differs from optical field oscillations due to nuclear dynamics i.e. vibrational WPI also [12].…”

“…An alternative way to retrieve coherent dynamics is by making use of the statistical variance of interferometric noise following randomly phased pulse-pair excitation (known as coherence observation by interference noise, or COIN) [9,10]. In contrast, here we report selective enhancement or suppression of fluorophores based on direct observation of the QI signal only [12][13][14], without any deliberate attempt to unravel pure coherent dynamics.…”

“…strong overlapping region) by periodically modulating the interpulse phase. This approach has been utilized in controlled gas-phase molecularfragmentation experiments [12] and studied in detail taking into account broadening of the spectral line shape as well as pulse profile, which is crucial in a condensed-phase environment [13,14]. In this Brief Report, we describe solutionphase fluorophore discrimination based on high-frequency QI observation and discuss its possible implementation in fluorescence microscopy.…”

Quantum Interference Signal from an Inhomogeneously Broadened System Excited by an Optically Phase-Controlled Laser-Pulse Pair

“…In another word, protection of molecular wavefunctions from the surrounding environment becomes important issue for realization of quantum control techniques in condensed phases. For that purpose, we aimed for the protection of the quantum phase of a guest molecule using the size-fit nano-space in a cyclodextrin nanocavity (Kiba et al, 2008). Cyclodextrins (α-, β-, or γ-CD), which are oligosaccharides with the hydrophobic interior and the hydrophilic exterior, are used as nanocavities because of their unique structures and the fact that six(α-), seven(β-), or eight(γ-) D-glucopyranose units determine the sizes whose diameters are ~5.7, 8.5, and 9.5 Å, respectively.…”

Spectral Narrowing of UV-Visible Absorption and Emission Spectra of Anthracene-Derivatives in β-Cyclodextrin Nanocavity: Effects of Host/Guest Stoichiometry

“…In our previous study, we reported the moderation of electronic decoherence of perylene in -CD aqueous solution at room temperature, as measured by an optical-phase-controlled pulse-pair quantum interferometer, combined with spectral lineshape analysis [16]. Interactions between guest molecules and surrounding environment are the origin of the electronic decoherence.…”