Stimulated emission depletion of two-photon excited states

Marsh, Richard J.; Armoogum, Daven A.; Bain, Angus J.

doi:10.1016/s0009-2614(02)01538-5

Cited by 24 publications

(36 citation statements)

References 13 publications

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“…86 The output power was controlled using neutral density wheels and filtered using a range of long-pass filters to remove Ti:sapphire harmonics and residual continuum (Schott RD530-630). The on-sample powers typically varied between 10 and 100 µW.…”

Section: Experimental and Computational Detailsmentioning

confidence: 99%

Two-Photon Transitions in Quadrupolar and Branched Chromophores: Experiment and Theory

et al. 2007

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A combined experimental and theoretical study is conducted on a series of model compounds in order to assess the combined role of branching and charge symmetry on absorption, photoluminescence, and twophoton absorption (TPA) properties. The main issue of this study is to examine how branching of quadrupolar chomophores can lead to different consequences as compared to branching of dipolar chromophores. Hence, three structurally related π-conjugated quadrupolar chromophores symmetrically substituted with donor end groups and one branched structure built from the assembly of three quadrupolar branches via a common donor moiety are used as model compounds. Their photophysical properties are studied using UV-vis spectroscopy, and the TPA spectra are determined through two-photon excited fluorescence experiments using femtosecond pulses in the 500-1000 nm range. Experimental studies are complemented by theoretical calculations. The applied theoretical methodology is based on time-dependent density functional theory, the Frenkel exciton model, and analysis in terms of the natural transition orbitals of relevant electronic states. Theory reveals that a symmetrical intramolecular charge transfer from the terminal donating groups to the middle of the molecule takes place in all quadrupolar chromophores upon photoexcitation. In contrast, branching via a central electron-donating triphenylamine moiety breaks the quadrupolar symmetry of the branches. Consequently, all Frank-Condon excited states have significant asymmetric multidimensional charge-transfer character upon excitation. Subsequent vibrational relaxation of the branched chromophore in the excited state leads to a localization of the excitation and fluorescence stemming from a single branch. As opposed to what was earlier observed when dipolar chromophores are branched via the same common electron-donating moiety, we find only a slight enhancement of the maximum TPA response of the branched compound with respect to an additive contribution of its quadrupolar branches. In contrast, substantial modifications of the spectral shape are observed. This is attributed to the subtle interplay of interbranch electronic coupling and asymmetry caused by branching.

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Section: Experimental and Computational Detailsmentioning

confidence: 99%

Two-Photon Transitions in Quadrupolar and Branched Chromophores: Experiment and Theory

et al. 2007

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“…Furthermore, stimulated emission depletion (STED) of the excited state has been introduced in fluorescence microscopy [13,14] to break the diffraction resolution barrier, [15,16] but has recently also been used to measure cross sections in the bulk. [17] We attained single molecule sensitivity with a scanning confocal setup fed by two synchronized pulse trains: a first pulse at a wavelength of l = 565 nm for excitation was followed by a red-shifted pulse at l = 778 nm for STED, both adapted to the spectrum (Figure 1 b) of the xanthene dye JA 26 (1). Efficient STED demands a STED pulse duration t of about 15 ps, [13,15] because this is significantly shorter than the nanosecond lifetime of S 1 , but much longer than the subpicosecond vibrational decay of S 0 * .…”

mentioning

confidence: 99%

Absolute Optical Cross Section of Individual Fluorescent Molecules

Kastrup

Hell

2004

Angew Chem Int Ed

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Besides having revealed transitions masked in the bulk, [1,2] optical spectroscopy of single molecules has enabled the observation of elementary molecular quantum events, such as the absorption and emission of a photon. [3][4][5][6] Single photon transitions are quantified by a cross section that can be regarded as the photon capture area of a molecule. Therefore, absolute optical cross sections can readily be measured in the bulk from the decrease (by absorption) or the gain (by stimulated emission) of the number of photons in a beam. [7] Unfortunately, this method is not applicable to individual molecules, because the resulting change in intensity is negligible. If the fluorescence quantum efficiency Q em is known, the molecular absorption cross section can be calculated from the fluorescence emission.[8] However, this method re-introduces the hallmark of ensemble averaging, because Q em is known only from the bulk. As a result, the absolute photon capture area of a specific molecule has remained elusive.Here we report on the measurement of absolute cross sections of stimulated emission at room temperature. No a priori information about the individual molecule is needed. In addition, we demonstrate the instant control of a molecules excited state by light and thus, as a matter of fact, also the viability of pump-probe experiments [9] with individual molecules at room temperature.Molecular optical absorption usually takes place from the vibrationally relaxed ground state S 0 to a hot Franck-Condon state S 1 * of the first excited singlet state (Figure 1 a). After vibrational relaxation, which occurs on a (sub)picosecond time scale, organic fluorophores emit within a few nanoseconds with a probability given by the fluorescence quantum yield. Alternatively, the S 1 !S 0 transition can be enforced by light, that is by stimulated emission.[10] Stimulated emission has been employed to probe the temporal evolution of the excited state in a pump-probe fashion, as well as to alter the fluorescence lifetime and anisotropy [11,12] of organic fluorophores in solution. Furthermore, stimulated emission depletion (STED) of the excited state has been introduced in fluorescence microscopy [13,14] to break the diffraction resolution barrier, [15,16] but has recently also been used to measure cross sections in the bulk. [17] We attained single molecule sensitivity with a scanning confocal setup fed by two synchronized pulse trains: a first pulse at a wavelength of l = 565 nm for excitation was followed by a red-shifted pulse at l = 778 nm for STED, both adapted to the spectrum (Figure 1 b) of the xanthene dye JA 26 (1). Efficient STED demands a STED pulse duration t of about 15 ps, [13,15] because this is significantly shorter than the nanosecond lifetime of S 1 , but much longer than the subpicosecond vibrational decay of S 0 * . Thus the S 1 $S 0 * system is effectively depleted. Figure 2 illustrates the ability of the STED pulse to "switch off" single fluorescent molecules embedded in a poly(vinyl alcohol) film. The image was ...

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“…In order to check the feasibility of high probability depletion, STED measurements were made in bulk sample with the aim of achieving a very large fractional population removal from the excited state (>90% depletion). The procedure for this experiment has been described in detail elsewhere 10,11 ; the apparatus used for these measurements is shown in figure 2. Following two-photon excitation (PUMP) from the partial output of an infra-red regenerative amplifier (Coherent RegA 9000), a fraction of the excited state population is stimulated back to the ground state via visible radiation (DUMP) from an Optical Parametric Amplifier (OPA, Coherent 9400).…”

Section: Experimental Apparatus Used For Bulk Sted Measurementsmentioning

confidence: 99%

Stimulated emission depletion and fluorescence correlation spectroscopy of a branched quadrupolar chromophore

et al. 2008

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Stimulated emission depletion (STED) and single molecule fluorescence correlation spectroscopy (FCS) are used to determine stimulated emission cross-sections and investigate non-radiative relaxation in a branched quadrupolar chromophore (OM77). The results are used as inputs to simulations of single molecule STED by which the feasibility of STED control of the single molecule fluorescence cycle can be assessed. Single molecule STED in OM77 is shown to be readily achievable; however its effectiveness in reducing triplet trapping is apparently mediated by fast non-radiative relaxation processes other than intersystem crossing and rapid quenching of the triplet state in a non-deoxygenated environment.

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Stimulated emission depletion of two-photon excited states

Cited by 24 publications

References 13 publications

Two-Photon Transitions in Quadrupolar and Branched Chromophores: Experiment and Theory

Two-Photon Transitions in Quadrupolar and Branched Chromophores: Experiment and Theory

Absolute Optical Cross Section of Individual Fluorescent Molecules

Stimulated emission depletion and fluorescence correlation spectroscopy of a branched quadrupolar chromophore

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