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Controlling the Spatial Orientation of Molecular Actuators: Polarized Photoisomerization of 2-Nitro-9-(2,2,2-triphenylethylidene)fluorene in a Thin Polymer Matrix Ali I. Ismail, Jordan H. Mantha,† Hyun Jong Kim, Thomas W. Bell, and Joseph I. Cline* Department of Chemistry, UniVersity of NeVada, Reno, NeVada 89557, United States ReceiVed: June 14, 2010; ReVised Manuscript ReceiVed: NoVember 13, 2010
The molecule 2-nitro-9-(2,2,2-triphenylethylidene)fluorene (NTEF) was studied as a potential light-driven molecular motor. Absorption at 355 nm causes a reversible spatial reorientation of the angular distribution of the dibenzofulvene rotor moiety of NTEF when immobilized in a poly(methyl methacrylate) (PMMA) matrix adsorbed on a fused silica surface in air at room temperature. The photoreorientation dynamics was probed by polarized normal incidence cavity ringdown spectroscopy (NICRDS) when the matrix was irradiated by linearly polarized “drive” light. Polarized drive irradiation at 355 nm creates a “hole” in the angular distribution of the molecular transition dipoles. Changing the polarization of the drive beam refills the hole, creating a new hole. A stochastic model was fitted to the experimental hole burning measurements to obtain a photoreorientation quantum yield (Φreorient ) 0.014). The photoreorientation process appears to be driven by photoisomerization of the exocyclic dibenzofulvene double bond of NTEF. Introduction Artificial molecular-scale switches and actuators have long been of interest in physics and chemistry, and significant progress recently has been made in artificial molecular switches,1-8,31 scissors,9 and ratchets.10 However, there are few successful examples of practical unidirectional molecular motors.11-24 Recent approaches either employ multiple chemical steps as in the work of Kelly and his group25,26 or require a sequence of thermal and photochemical steps as in the work of Feringa and his co-workers.27 Feringa has reported a light-driven motor that binds on a gold surface that makes a full 360° rotation in four steps28,29 and can be adapted to drive molecular nanocars.30 Light-driven molecular actuators and motors typically exploit the photoisomerization of a C-C double bond as in stilbene2,3 and azobenzene,4-8 or the opening and closing of a cyclic moiety such as the photoisomerization of photochromic spiropyran compounds.32,33 Our group has been studying the utility of a family of substituted dibenzofulvenes for applications as light-controlled switches and actuators.34 Our earlier studies examined their photoisomerization in liquid organic solvents.35 In this paper, we report the first studies of these substituted dibenzofulvenes in the condensed phase, immobilized in a PMMA film. Many potential applications require surface-immobilized rotors to interact with other device components such as conductors or logic gates or as sensing elements exposed to a mobile fluid phase. It is also of interest to consider the collective excitation of ensembles of rotors in applications such as controllable optical devices and for information storage. In this work, photoisomerization is detected by polarized normal incidence ringdown spectroscopy (NICRDS), a technique developed in our laboratory for probing the angular distribution of adsorbed actuators by polarized absorption spectroscopy. We have previously applied NICRDS to probe the photoswitching of immobilized photochromic spiropyrans.36 * To whom correspondence should be addressed. E-mail:
[email protected]. † Current address: Air Force Research Laboratory, Hanscom Air Force Base, Bedford, MA 01731.
Here we use (Z)-2-nitro-9-(2,2,2-triphenylethylidene)fluorene (hereafter abbreviated Z-NTEF) as a motor prototype. In describing the functionality of NTEF, shown in Figure 1a, we can decompose its structure into three components: a “stator” consisting of the trityl moiety, a “drive axis” consisting of the exocyclic double bond, and a “rotor” fluorene moiety. In contrast to several theoretical studies predicting that photoisomerization of fulvene would be extremely inefficient,37-41 we have shown that photoisomerization of dibenzofulvenes has a large quantum yield depending on the attached substituents and the excitation wavelength.34,35 The 2-nitrodibenzofulvene chromophore in the NTEF molecule is of special utility as a molecular actuator because of its photostability and high quantum efficiency and because the E and Z isomers show similar absorbance spectra in the near-UV region, as shown in Figure 2. By appropriate modification of the trityl stator moiety to form a chiral ratchet structure, NTEF derivatives have the potential to power unidirectional, lightdriven motors. Experimental Section The molecule (Z)-2-nitro-9-(2,2,2-triphenylethylidene)fluorene (NTEF) was prepared as described by Everhart et al.35 NTEF photoisomerization was studied at room temperature in a thin poly(methyl methacrylate) polymer (PMMA) film in ambient air. The film was prepared from a 1 mg/mL solution of PMMA (average MW ) 120 000 g/mol) in spectroscopic grade toluene solvent. The typical concentration of NTEF in the coating solution is in a 1:10 NTEF:PMMA ratio by mass. A 50 µL sample of this solution was spin-coated (1500 rpm for 60 s) onto high-quality, flat, fused silica substrates (CVI, surface flatness of 10-5, 5 s deviation between the two surfaces). The thickness of the polymer layer is expected to be in the range of 10-50 nm, based on previous studies of films prepared with the same spin coating recipe.42 Prior to being coated, substrates were cleaned by being wiped with methanol, sonicated for 1 h in an aqueous soap solution, rinsed with distilled water, cleaned in an aqua-regia solution
10.1021/jp1054777 2011 American Chemical Society Published on Web 01/06/2011
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Figure 1. (a) Structures of (Z)- and (E)-2-nitro-9-(2,2,2-triphenylethylidene)fluorene (NTEF) identifying key torsion angles θ (rotation about the exocyclic CdC bond of dibenzofulvene) and φ (the geared rotation about the C-C bond connecting the dibenzofulvene rotor moiety to the trityl stator). The Z and E isomers are interconverted by light absorption at 355 nm. (b) 2-Nitrofluorene, a nonphotoisomerizing mimic of the dibenzofulvene rotor moiety of NTEF. The transition dipole vector, µˆ , lies in the plane of the fluorene moieties of two species, although its actual orientation in that plane is not necessarily as depicted above.
for 1 h followed by sequential rinsing with doubly distilled water and a concentrated ammonia solution, and then finally dried in an oven at 90 °C. The coated fused silica substrate was placed in the center of the cavity ringdown spectrometer, as described in ref 36. The cavity consists of two parallel, highly reflective mirrors (Los Gatos Research, R ) 99.95% at 355 nm, radius of curvature of 1.0 m). The substrate was aligned to be normal to the cavity axis using precision rotary stages. Achieving a normal incidence geometry is critical to maximizing the lifetime of photons trapped in the optical cavity, and hence the sensitivity of the absorption measurements. The full details of the alignment procedure were described previously.36 The distance between the two mirrors was 75 cm. The experimental apparatus is shown in Figure 3. The experiments are of the “pump-probe” type. A linearly polarized drive laser pulse was used to excite the sample with pulse energies between 12 and 300 µJ. The probe beam consists of a circularly polarized pulse injected into the NCRDS cavity to measure polarized absorption.36 Both pulses were obtained from the third harmonic (355 nm) of a 5 ns/pulse, 10 Hz repetition rate, with the Nd:YAG laser. As defined in Figure 3, the drive beam direction is kˆd and the probe beam direction is kˆp, and the beams are nearly counter-propagating. The two beams intersect at the coated surface of the fused silica substrate. At the substrate, the drive beam spot size diameter was 3.0 mm. The probe beam spot size was smaller in diameter and hits the center of the drive beam spot. In our NICRDS apparatus, the drive and probe breams cannot be completely collinear, so that kˆd is not perfectly normal to the substrate. Its deviation from normal was 7°. The laboratory-frame angle of the linear drive polarization was controlled by a half-wave plate. The probe pulse passed through a pinhole spatial filter to improve its
transverse mode quality and then was converted to circular polarization by a quarter-wave plate immediately prior to entering the cavity. Following the second cavity mirror, a Glan polarizing prism separated the escaping probe light into its horizontal (H) and vertical (V) polarization components, which were measured by separate photomultiplier detectors. The individual H- and V-polarized ringdown decay transients were simultaneously recorded by separate channels of a two-channel digital oscilloscope and individually transferred to a computer. Individual decay transients were fit to an exponential decay to obtain the cavity lifetime, τ. A “blank” cavity lifetime, τb, was measured for each channel at the start of the experiment, prior to the irradiation by drive pulses. The reflectivity of the cavity mirrors, scattering by the PMMA matrix, and substrate scattering all contribute to τb, in addition to the initially isotropic absorbance of the NTEF molecules immobilized in the PMMA film. After irradiation by the drive pulse, the cavity lifetime, τ, is converted to a change in absorbance relative to the blank, making use of the relation43
a)
( )
l τb - τ c τbτ
(1)
where l is the cavity length, c is the speed of light, τb is the blank lifetime, and τ is the measured lifetime. Using eq 1, the initial absorbance of the initially isotropic NTEF ensemble, a, is defined as zero. Following irradiation by the drive beam, a change is observed in both the vertical and the horizontal absorbance. Figure 4a shows an example of the measured NICRDS lifetime, τ(V), for the vertically polarized probe as a function of irradiation time for NTEF in a PMMA film on a fused silica substrate. Figure 4b shows the corresponding change in absorbance, a(V), at 355 nm. Typical cavity lifetimes with the substrate and analyte present were 0.2-1.0 µs, while an empty cavity has a lifetime of ∼4.0 µs. Results
Figure 2. UV-vis absorption spectra of Z- and E-NTEF in acetonitrile taken from ref 35.
Figure 5 shows the measured change in probe absorbance, a, for both vertical and horizontal polarizations. Starting at time zero the sample is irradiated by a vertically polarized drive beam. Initially, the H absorbance, a(H), increases and the V absorbance, a(V), decreases; however, the absorbance for both polarizations decreases over long time scales. To focus on the polarization effects instead of the long-term absorbance decrease, the right panel of Figure 5 shows the difference absorbances, ∆a(V) and ∆a(H), defined by subtracting the polarizationaveraged absorbance at time t from the either the V- or H-polarized absorbance at time t:
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Figure 3. Polarized NICRDS apparatus with associated polarization and detection optics. kˆp is the propagation direction of the circularly polarized probe beam, and kˆd is the propagation direction of the linearly polarized drive light. The optics λ/2 and λ/4 are half- and quarter-wave plates, respectively. GP is a Glan prism.
Figure 4. (a) NICRDS lifetime, τ(V), for V-polarized probe light measured as a function of time following irradiation by V-polarized 355 nm drive light starting at time zero. (b) Corresponding absorbance change, a(V), at 355 nm obtained using eq 1.
∆a(V) ) -∆a(H) )
a(V) - a(H) 2
(2)
We observed that the difference absorbance of the probe beam consistently increases in the direction orthogonal to drive beam polarization, and the absorbance decreases in the direction parallel to the drive beam polarization. Figure 6 shows that alternating the polarization of the drive beam causes an alternation in the relative probe absorbance measured in the V and H polarizations. However the polarization-averaged absorbance decreases steadily with drive beam irradiation, in a manner independent of the drive beam polarization. At 355 nm, the transition dipole vector, µˆ , of NTEF lies in the plane of the two benzene rings of the 2-nitrofluorene rotor moiety. The linearly polarized drive light preferentially energizes molecules having rotor moieties parallel to εˆ d, the electric vector of the drive light. We hypothesize that absorption of light moves µˆ in a new direction. For the ensemble of surface-adsorbed molecules, this causes reversible “hole burning” in the angular distribution of their transition dipoles. Changing the polarization of the drive beam refills the existing hole and creates a new hole in the direction parallel to the new polarization, as shown in Figure 6. Alternating the drive beam polarization (vertical and horizontal) yields multiple cycles of hole burning and refilling. The polarization-averaged absorbance shows a first-
order decay, which we attribute to both photodecomposition of the NTEF and PMMA-NTEF interactions. The population decay is evident in the decreasing amplitude of the envelope containing the ∆a oscillations in Figure 6b. The change in interactions may result from photoannealing of the PMMA film that slightly shifts the NTEF absorption spectrum, resulting in an apparent decay in the polarization-averaged absorbance at 355 nm during drive irradiation. As mentioned in the Experimental Section and as depicted in Figure 7, both probe polarizations are s-polarized with respect to the coated surface of the substrate. As shown in Figure 3, the electric vector of the H-polarized drive light has a small p-polarized component with respect to substrate surface, because of the slightly non-normal drive beam geometry [∠(kˆd,kˆp) ) 7°]. However, the V-polarized drive light is entirely s-polarized. Consequently, H-polarized drive light creates a distribution of rotors not as efficiently detected as a distribution created by V-polarized drive light: as viewed by the probe beam, Vpolarized drive light polarization “digs a deeper hole” than H-polarized drive light. This is evident in Figure 6, which shows that the amplitudes of the polarization differences, ∆a(H), are smaller than expected relative to ∆a(V). The origin of this effect is depicted in Figure 8 and is a result of the imperfect alignment of the H-polarized drive hole with the H-polarized probe light. To study the drive power dependence of this orientational hole burning, the kinetics of the first hole burning cycle was studied as a function of drive pulse energy. Figure 9 shows that the magnitude of the difference absorption and rate of angular reorientation increases with increasing drive pulse energy. The rate of decay of the polarization-averaged absorbance also increases with the drive beam energy. As discussed below, both of these quantities depend linearly on drive beam pulse energy. The persistence of the angular hole in the absence of drive beam irradiation is shown in Figure 10. Once created, the angular hole disappears with a qualitatively biexponential behavior when drive irradiation is ended. The hole reappears when the sample is re-exposed to the drive beam. We attribute the disappearance of the angular hole to randomization of the rotor angular distribution due to thermal motions of the rotors in the matrix. An important question is whether photoisomerization is essential to angular hole burning or whether the effect is primarily due to local heating by absorption of the drive light. To investigate this issue, we studied PMMA films containing a similar chromophore that does not photoisomerize. The molecule 2-nitrofluorene (see Figure 1b) is not able to undergo E-Z photoisomerization. Accounting for the molar absorptivity of 2-nitrofluorene (approximately half of that of NTEF) and its molecular weight relative to that of NTEF, films of 2-nitrofluorene and NTEF having the same mass concentration have nearly the same optical density. Figure 11 shows a comparison
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Figure 5. Hole burning in the angular distribution of the NTEF transition dipole ensemble with a V-polarized drive beam measured using a drive pulse energy of 100 µJ/pulse (photon flux F ) 2.5 × 1015 cm-2/pulse) in a PMMA film on a fused silica substrate. (a) Absorbances changes, a(V) and a(H), corresponding to the measured absorbance changes for polarized probe detection upon drive irradiation. (b) Polarization difference absorbances, ∆a(V) and ∆a(H), corresponding to the difference of a(V) and a(H) from the polarization-averaged absorbance, a(avg).
Figure 6. Alternation of drive beam polarization to obtain cycles of angular hole burning and refilling in the NTEF transition dipole ensemble in a PMMA film on a fused silica substrate. (a) Absorption changes a(V) and a(H) measured with vertical and horizontal probe light, respectively, and polarization-averaged absorbance, a(avg). (b) Difference absorptions ∆a(V) and ∆a(H). The energy of the 355 nm drive beam is 100 µJ/pulse (photon flux F ) 2.5 × 1015 cm-2/pulse).
Figure 8. Depiction of the origin of differing detection efficiencies for angular holes created by V- and H-polarized drive light. The H-polarized drive beam, kˆd, is not perfectly collinear with kˆp, so that the resulting angular hole is less efficiently detected by the probe beam than a hole created by V-polarized drive light. Figure 7. Geometry definitions for the polarized NICRDS experiment. The analyte is immobilized on a surface in the Y-Z plane. The orientation of the transition dipole of a single molecular actuator, µˆ i, is specified by its polar and azimuthal angles θi and φi. The drive and probe beam propagation directions are kˆd and kˆp, respectively. Also shown are the associated V- and H-polarized electric vectors, εˆ d and εˆ p, for the drive and probe beams, respectively. V polarization is defined to be parallel to Zˆ and H polarization to be in the X-Y plane. The drive propagation axis is at an angle of 7° from the surface normal (φ).
of angular hole burning for 2-nitrofluorene and NTEF molecules, both at a concentration of 1:60 by mass concentration in PMMA. In the first oscillation, the polarization difference for 2-nitrofluorene is ∼6% of that obtained in the NTEF experiments. Moreover, in the later oscillations, the polarization effect becomes even smaller (7° is consistent with the p-polarized drive beam electric vector εˆ d tilted at an angle larger than 7° with respect to the plane of the surface. Although ordinary Snell’s law interfacial refraction from air into PMMA will cause a deflection of kd (and εˆ d for p-polarized light), the effect is relatively small with kˆd becoming more normal to the surface and εˆ d lying closer to the surface plane. In contrast, the best fit of φ to our experimental data
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Figure 12. Fits of the stochastic model to (a) the measured V- and H-polarized absorbance changes, a(V) and a(H), respectively. (b) Corresponding polarization differences ∆a(V) and ∆a(H) for the experimental data and the simulation. Experimental data are shown as circles and fits as solid traces. The V absorbance is colored red and the H absorbance blue. The experimental drive beam pulse energy was 100 µJ/pulse (photon flux F ) 2.5 × 1015 cm-2/pulse). The values of the cross sections σreorient and σdecomp and thermal relaxation rate constant ktherm are given in Table 1. For background absorption in eq 7, b ) 3.0 × 10-3 and r ) 1.8 × 10-5 pulse-1. Panels c and d show the same experimenal data along with the fit to the stochastic model with a drive angle of incidence (φ) of 20° from the surface normal.
TABLE 1: Kinetic Parameters for the 355 nm Photoisomerization Dynamics of NTEF in a PMMA Film at 23 ( 1 °Ca σreorient σdecomp ktherm Φreorient Φdecomp a
(9.4 ( 0.3) × 10-19 cm2 (7.5 ( 2.2) × 10-21 cm2 (5.6 ( 1.9) × 10-3 s-1 0.014 ( 0.003 (1.1 ( 0.8) × 10-4
Reported uncertainties are 95% confidence limits.
shows an apparent deflection toward larger angles. One hypothesis for the unexpectedly large deflection is a significant imaginary component to the 355 nm index of refraction of the polymer film, due to absorbance in the polymer film. Although the film is thin with a small absorbance, it has a high concentration of absorbers with a large absorption cross section. The resulting complex index of refraction can lead to an electric field orientation and an “effective” propagation direction quite different than that predicted by Snell’s law. The theory
describing this effect is complicated, and predictions require knowledge of material properties that are unknown in our system;46 therefore, we make no attempt to calculate a “corrected” φ value. However, we note that an experiment in which the concentration of NTEF absorbers in the film is decreased by a factor of 6 causes a change in the optimized value of φ in the stochastic model, consistent with the hypothesis of a significant imaginary component to the index of refraction in the PMMA film. Discussion and Conclusion Our previous liquid phase studies of substituted dibenzofulvene photoisomerization34,35 have shown their potential as lightcontrolled switches and actuators. This study demonstrates these properties persist in high-viscosity environments when adsorbed to surfaces, demonstrating the practical utility of substituted dibenzofulvene as controllable actuators for molecular-scale devices.
Figure 13. (a) Fitted isomerization probability, kreorient, and (b) fitted decomposition probability, kdecomp, obtained from data sets measured at different drive beam pulse energies.
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Several studies have reported photo-orientation by polarized photoisomerization of relatively thin films.47-55 We demonstrate not only photo-orientation from an isotropic ensemble creating an angular hole but also the ability to refill it, creating another hole in a different direction by changing the polarization of the drive light. To the best of our knowledge, this is the first study to show such complete control over the ordering of the angular distribution of transition dipoles. This study is also distinct in that our film is significantly thinner than those of previous studies. The control experiments in which 2-nitrofluorene was used instead of the NTEF actuator molecule suggest that the polarization effect observed in the NTEF experiments is predominately due to the photoisomerization of the double bond resulting in spatial reorientation of the dibenzofulvene rotor moiety. Studies currently underway in our laboratory in which the photoisomerization of a similar (2,2,2-triphenylethylidene)fluorene can be chemically controlled confirm that the angular hole burning in these species arises from photoisomerization, not simple absorption-induced heating of the polymer matrix. We have studied the photoisomerization of NTEF in roomtemperature acetonitrile. The average of the ΦEfZ and ΦZfE quantum yields is 0.17 (Φisom), ∼12 times the photoreorientation quantum yield Φreorient measured by polarized NICRDS in a PMMA matrix. There are several reasons that Φreorient is expected to be smaller than Φisom. First, not all photoisomerization events necessarily result in photoreorientation of the dibenzofulvene rotor moiety. The trityl stator moiety (see Figure 1a) may move instead, or successful rotary motion of the dibenzofulvene may result in its transition dipole being very close to its initial angular location. Photoisomerization necessarily requires large amplitude nuclear motions that can sweep out large volumes. The PMMA matrix is expected to be more viscous than acetonitrile, and this may reduce the quantum yield for the photoisomerization process that appears to be necessary for efficient photoreorientation. The NTEF actuator molecule appears to be relatively photorobust, with a Φdecomp of 1.1 × 10-4. In an acetonitrile solution, photodecomposition of NTEF could be detected only under oxygen-saturated conditions; suggesting that at least part of the photodecomposition observed in PMMA could be due to photo-oxidation. One objective of these experiments is to ultimately study actuator species in which a functionalized stator moiety is chemically bound to the substrate surface, for example, by silanization. In this case of immobilized stators, only the rotor moiety moves upon photoisomerization, so that larger Φreorient values are expected. The polarized NICRDS technique potentially offers the sensitivity to detect the motion of this adsorbed monolayer of rotors.36 In particular, when the immobilized actuators are axially oriented normal to the surface, it is possible to directly detect unidirectional (clockwise or counterclockwise) motion of their rotor moieties. This is of intense interest in the probing of the operation of true, unidirectional molecular motors. Acknowledgment. This research was supported by the National Science Foundation (#CHE-0210549). References and Notes (1) Kawata, S.; Kawata, Y. Chem. ReV. 2000, 100, 1777. (2) Erdelyi, M.; Varedian, M.; Skoeld, C.; Niklasson, I. B.; Nurbo, J.; Persson, A.; Bergquist, J.; Gogoll, A. Org. Biomol. Chem. 2008, 6, 4356– 4373. (3) Gulino, A.; Lupo, F.; Condorelli, G. G.; Fragala, M. E.; Amato, M. E.; Scarlata, G. J. Mater. Chem. 2008, 18, 5011–5018.
Ismail et al. (4) Urbas, A.; Tondiglia, V.; Natarajan, L.; Sutherland, R.; Yu, H.; Li, J.-H.; Bunning, T. J. Am. Chem. Soc. 2004, 126, 13580. (5) Wan, P.; Jiang, Y.; Wang, Y.; Wang, Z.; Zhang, Xi. Chem. Commun. 2008, 44, 5710–5712. (6) Renner, C.; Moroder, L. ChemBioChem 2006, 7, 868–878. (7) Reddy, D. R.; Maiya, B. G. Chem. Commun. 2001, 1, 117–118. (8) Jaycox, G. D. Polym. Prepr. (Am. Chem. Soc., DiV. Polym. Chem.) 2001, 42, 667–668. (9) Muraoka, T.; Kinbara, K.; Kobayashi, Y.; Aida, T. J. Am. Chem. Soc. 2003, 125, 5612–5613. (10) Serreli, V.; Lee, C.-F.; Kay1, E. R.; Leigh, D. A. Nature 2007, 445, 523–527. (11) Bell, T. W.; Cline, J. I. ACS Symp. Ser. 2009, 1025 (Chemical Evolution II), 233–248. (12) Balzani, V.; Credi, A.; Venturi, M. Chem. Soc. ReV. 2009, 38, 1542– 1550. (13) Vives, G.; Jacquot de Rouville, H.-P.; Carella, A.; Launay, J.-P.; Rapenne, G. Chem. Soc. ReV. 2009, 38, 1551–1561. (14) Vives, G.; Carella, A.; Launay, J.-P.; Rapenne, G. Coord. Chem. ReV. 2008, 252, 1451–1459. (15) Semeraro, M.; Silvi, S.; Credi, A. Front. Biosci. 2008, 13, 1036– 1049. (16) Feringa, B. L.; van Delden, R. A.; ter Wiel, M. K. J. Pure Appl. Chem. 2003, 75, 563–575. (17) Saha, S.; Stoddart, J. F. Chem. Soc. ReV. 2007, 36, 77–92. (18) Jacquot de Rouville, H.-P.; Vives, G.; Rapenne, G. Pure Appl. Chem. 2008, 80, 659–667. (19) Agrawal, U. C.; Nigam, H. L. J. Indian Chem. Soc. 2008, 85, 677– 690. (20) Hoki, K.; Yamaki, M.; Fujimura, Y. Springer Ser. Chem. Phys. 2008, 89, 92–112 (Progress in Ultrafast Intense Laser Science, Volume 3). (21) Amelia, M.; Semeraro, M.; Silvi, S.; Credi, A. Chimia 2008, 62, 204–209. (22) Credi, A. Aust. J. Chem. 2006, 59, 157–169. (23) Kay, E. R.; Leigh, D. A. Pure Appl. Chem. 2008, 80, 17–29. (24) Balzani, V.; Venturi, M.; Credi, A. Molecular DeVices and Machines: A Journey into the Nanoworld; Wiley-VCH: Weinheim, Germany, 2003. (25) Kelly, T. R.; De Silva, H.; Silva, R. A. Nature 1999, 401, 150– 152. (26) Kelly, T. R.; Cai, X.; Damkaci, F.; Panicker, S. B.; Tu, B.; Bushell, S. M.; Cornella, I.; Piggott, M. J.; Salives, R.; Cavero, M.; Zhao, Y.; Jasmin, S. J. Am. Chem. Soc. 2007, 129, 376–386. (27) Feringa, B. L.; Koumura, N.; Zijstra, R. W.; Delden, R. A.; Harada, N. Nature 1999, 401, 152–154. (28) van Delden, R. A.; ter Wiel, M. K. J.; Pollard, M. M.; Vicario, J.; Koumura, N.; Feringa, B. L. Nature 2005, 437, 1337–1340. (29) Pijper, T. C.; Pijper, D.; Pollard, M. M.; Dumur, F.; Davey, S. G.; Meetsma, A.; Feringa, B. L. J. Org. Chem. 2010, 75, 825–838. (30) Vives, G.; Tour, J. M. Acc. Chem. Res. 2009, 42, 473–487. (31) Silvi, S.; Venturi, M.; Credi, A. J. Mater. Chem. 2009, 19, 2279– 2294. (32) Zhou, W.; Chen, D.; Li, J.; Xu, J.; Lv, J.; Liu, H.; Li, Y. Org. Lett. 2007, 9, 3929–3932. (33) Zhu, M.-Q.; Zhu, L.; Han, J. J.; Wu, W.; Hurst, J. K.; Li, A. D. Q. J. Am. Chem. Soc. 2006, 128, 4303–4309. (34) Barr, J. W.; Bell, T. W.; Catalano, V. J.; Cline, J. I.; Phillips, D. J.; Procupez, R. J. Phys. Chem. A 2005, 109, 11650–11654. (35) Everhart, S. C.; Kim, H.-J.; Procupez, R.; Stanbery, W. A.; Mishler, C. H.; Frost, B. J.; Bell, T. W.; Cline, J. I., submitted for publication. (36) Mantha, J. H.; Ismail, A. I.; Cline, J. I. J. Phys. Chem. A 2010, 10.1021/jp105474c. (37) Bearpark, J.; Bernardi, F.; Olivucci, M.; Robb, M. A.; Smith, B. R. J. Am. Chem. Soc. 1996, 118, 5254. (38) Sicilia, F.; Bearpark, M. J.; Blancafort, L.; Robb, M. A. Theor. Chem. Acc. 2007, 118, 241–251. (39) Paterson, M. J.; Bearpark, M. J.; Robb, M. A.; Blancafort, L. J. Chem. Phys. 2004, 121, 11562–11571. (40) Deeb, O.; Cogan, S.; Zilberg, S. Chem. Phys. 2006, 325, 251–256. (41) Sumita, M.; Saito, K. J. Chem. Theory Comput. 2008, 4, 42–48. (42) Spangler, L. L.; Torkelson, J. M.; Royal, J. S. Polym. Eng. Sci. 1990, 30, 644. (43) Muir, R. N.; Alexander, A. J. Phys. Chem. Chem. Phys. 2003, 5, 1279. (44) Burtt, K. D. Diss. Abstr. Int., B 2006, 67, 1455. (45) As an example flux calculation, at a typical drive pulse energy of 100 µJ/pulse and a drive beam spot diameter of 3.0 mm, the photon flux (F) equals 2.5 × 1015 cm-2/pulse. (46) Born, M.; Wolf, E. Principles of Optics; Pergamon: New York, 1975. (47) Sakket, Z.; Wood, J.; Knoll, W. J. Phys. Chem. 1995, 99, 17226– 17234.
Spatial Orientation of Molecular Actuators (48) Tawa, K.; Kamada, K.; Sakaguchi, T.; Ohta, K. Appl. Spectrosc. 1998, 52, 1536–1540. (49) Perny, S.; Le Barny, P.; Delaire, J.; Buffeteau, T.; Sourisseau, C. Liq. Cryst. 2000, 27, 341–348. (50) Sekkat, Z.; Ishitobi, H.; Kawata, S. Opt. Commun. 2003, 225, 403. (51) Bobrovsky, A.; Shibaev, V.; Stumpe, J. J. Phys. Chem. A 2006, 110, 2331–2336. (52) Bossi, M. L.; Murgida, D. H.; Aramend, P. F. J. Phys. Chem. B 2006, 110, 13804–13811.
J. Phys. Chem. A, Vol. 115, No. 4, 2011 427 (53) Ishitobi, H.; Sekkat, Z.; Kawata, S. J. Chem. Phys. 2006, 125, 164718. (54) Rutloh, M.; Zebger, I.; Hoffmann, U.; Stumpe, J.; Siesler, H. W. Polym. Prepr. (Am. Chem. Soc., DiV. Polym. Chem.) 1998, 39, 324–325. (55) Kawamoto, M.; Sassa, T.; Wada, T. J. Phys. Chem. B 2010, 114, 1227–1232.
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