Optical, Mechanical, and Opto‐Mechanical Switching of Anchored Dithioazobenzene Bridges

Turanský, Robert; Konôpka, Martin; Doltsinis, Nikos L.; Štich, Ivan; Marx, Dominik

doi:10.1002/cphc.200900690

Cited by 36 publications

(58 citation statements)

References 29 publications

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“…This analysis shows that in a dense medium, photon-induced molecular shape change of the azo core occurs on the 10 ps time scale, sufficiently slow that it produces a coherent force transient on neighbouring molecules (as opposed to molecular vibrations 49,50 ), depositing B2 eV of mechanical energy, enough to produce an orientational event with an effective local temperature of T ¼ 800 K. If only rotations about short molecular axes were so excited (an unlikely occurrence), then an upper estimate of B30 molecules could be directly involved. As, in general, there are translational, other rotational and low-lying vibrational modes that will also be excited, the actual number of participating molecules must be smaller, probably limited to groups of nearest neighbours (B7 molecules).…”

Section: Sam Glassy Relaxation: Two Distinct Barrier-crossing Processesmentioning

confidence: 94%

“…Absorption of a photon at 514 nm deposits an energy of hn ¼ 2.4 eV into a dMR azo core, enough to excite a single harmonic degree of freedomto T ¼ hn=k B ¼ 29,000 K. Some fraction of this energy appears in a form that locally tests the molecular orientational barrier distribution at the effective temperature of T CP B800 K. Fast spectroscopy [45][46][47] , quantum/molecular dynamic simulation 18,48 and molecular dynamic simulation 17 provide a semi-quantitative picture of this process, indicating that it is principally mechanical, with the photon energy appearing as a coherent force acting transiently on the environment of the absorbing molecule 49,50 , as follows. Upon photon absorption and electronic excitation, the azo core returns to the ground electronic manifold in a transition state configuration from which coherent change of the intra-molecular configuration takes place along one of several possible paths,for example, trans to cis or trans to trans, all of which reduce the internal potential energy by B2 eV (45 kcal per mole), representing almost all of the absorbed photon energy 18,48 .…”

Section: Sam Glassy Relaxation: Two Distinct Barrier-crossing Processesmentioning

confidence: 99%

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Athermal photofluidization of glasses

et al. 2013

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Azobenzene and its derivatives are among the most important organic photonic materials, with their photo-induced trans-cis isomerization leading to applications ranging from holographic data storage and photoalignment to photoactuation and nanorobotics. A key element and enduring mystery in the photophysics of azobenzenes, central to all such applications, is athermal photofluidization: illumination that produces only a sub-Kelvin increase in average temperature can reduce, by many orders of magnitude, the viscosity of an organic glassy host at temperatures more than 100 K below its thermal glass transition. Here we analyse the relaxation dynamics of a dense monolayer glass of azobenzene-based molecules to obtain a measurement of the transient local effective temperature at which a photo-isomerizing molecule attacks its orientationally confining barriers. This high temperature (T loc B800 K) leads directly to photofluidization, as each absorbed photon generates an event in which a local glass transition temperature is exceeded, enabling collective confining barriers to be attacked with near 100% quantum efficiency.

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Section: Sam Glassy Relaxation: Two Distinct Barrier-crossing Processesmentioning

confidence: 94%

Section: Sam Glassy Relaxation: Two Distinct Barrier-crossing Processesmentioning

confidence: 99%

Athermal photofluidization of glasses

et al. 2013

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“…The starting point of our modeling of the gold-DAB-gold junction were the lowtemperature geometries of the junction in trans/cis conformations sampled from the tra-5 jectories previously used to study the opto-mechanical switching [9,10]. The gold tips were prepared in a MCBJ-type procedure using an empirical effective medium theory potential [49] together with Langevin dynamics.…”

Section: A Junction Geometrymentioning

confidence: 99%

“…However, use of these optoelectronic devices requires that their operation be reversible. While there are numerous molecules capable of photo-switching in gas-phase, their embedding in junction by anchoring to tips or surfaces may compromise their switching capability either due to mechanical hindrance [9,10] or quenching of excited state in the photo-switchable process [21].…”

Section: Introductionmentioning

confidence: 99%

“…Additional question-marks mar the photo-switchability of anchored AB photo-switches. While anchored polymeric chains of AB molecules are easily switchable optically [28], switching of their tip/surface-anchored single AB counterpart was found to be mechanically hindered [9,10]. In order to eliminate the mechanical hindrance a variant of an anchored single-molecule AB switch using a conducting carbon nano-tube support for one electrode was proposed [7].…”

Section: Introductionmentioning

confidence: 99%

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Rigidity of the conductance of an anchored dithioazobenzene optomechanical switch

2013

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Reversible opto-mechanical molecular switch based on a single azobenzene molecule suspended via thiolate links between realistic models of gold tips is investigated. Using a combination of the transfer matrix technique and density functional theory we focus on conductance of the nano-device in the two (meta)stable cis and trans junction conformations. We find the conductance of both conformations to be broadly similar. In qualitative agreement with related experiments, we find that the same nano-device with one/two methylene linker group(s) inserted on one/both ends of the azobenzene molecule is driven into tunneling regime and reduces the conductances by up to two orders of magnitude, again almost uniformly for both conformations. These results clarify the huge differences in switching ratios found previously and indicate that this nano-device is not particularly suited for use as a molecular switch based on conductance change.

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Unraveling a Chemically Enhanced Photoswitch: Bridged Azobenzene

2010

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The possibility to reversibly photoisomerize azobenzene (AB) has made it one of the most ubiquitous light-sensitive molecular switches. [1][2][3][4][5][6][7][8][9][10] Opto-and nanomechanical devices [9,10] that convert light to mechanical action, for instance, exploit the considerable stretching of AB on Z!E isomerization. In biochemical studies, AB has been integrated into synthetic peptides and foldamers to photocontrol their conformational dynamics. [6,11] Photoaddressable materials such as image-storage media are often based on AB functional units. [12,7] For all of the above applications of the AB photoswitch it is of paramount importance to ensure that the photoisomerization process [13][14][15] is fast and has a high quantum yield.Recently, a greatly enhanced E!Z quantum yield F ABÀC 2 E!Z was reported for a bridged azobenzene (AB-C 2 in Figure 1) in the S 1 state compared to the parent molecule AB. [16] This finding may seem surprising at first, as the structural changes involved in isomerization are expected to be hindered by the restriction due to the presence of a bridge interconnecting the phenyl rings. It thus seems remarkable to observe a much larger quantum yield of bridged AB-C 2 compared to AB itself. Herein we demonstrate that, counterintuitively, the bridge does not hinder photoisomerization. On the contrary, it suitably preorients the phenyl rings such that AB-C 2 can more easily undergo E!Z isomerization, so that not only an enhanced quantum yield F ABÀC 2 E!Z but also ultrashort S 1 lifetimes result.Similar to earlier work [17][18][19] we investigated the photodynamics of E-AB-C 2 in the S 1 excited state in the gas phase employing nonadiabatic [20,21] ab initio molecular dynamics (AIMD), [22] whereby "on-the-fly" nonadiabaticity is introduced by using Tullys fewest-switches surface hopping [23] to couple S 1 and S 0 . In particular, the fewest-switches method has been demonstrated [13][14][15] to describe satisfactorily, both mechanistically and quantitatively, photoisomerization of the parent compound AB, including the E!Z and Z!E quantum yields and the timescales involved. Here, all calculations were carried out with the CPMD package [24] by employing a cubic 18 periodic box, the PBE functional, and plane waves with dual-space pseudopotentials. [22] A total of 30 nonadiabatic simulations of at least 500 fs were performed microcanonically in the Born-Oppenheimer mode with a time step of 2 a.u., with initial conditions sampled from a canonical ground state run at 300 K.A prerequisite for the dynamics is an extensive validation of the S 0 and S 1 potential energy surfaces, which was done in much detail [18] for the parent compound by comparison with CASPT2 data. [17][18][19] An analogous analysis for the E-AB-C 2 derivative confirms that the DFT excitation energy (2.59 eV) is again in good agreement with both CASPT2 (2.52 eV) and experiment (2.53 eV). On chemical modification of AB to form AB-C 2 (i.e., addition of a À CH 2 CH 2 À bridge in ortho position of the phenyl rings) the E isomer b...

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Optical, Mechanical, and Opto‐Mechanical Switching of Anchored Dithioazobenzene Bridges

Cited by 36 publications

References 29 publications

Athermal photofluidization of glasses

Athermal photofluidization of glasses

Rigidity of the conductance of an anchored dithioazobenzene optomechanical switch

Unraveling a Chemically Enhanced Photoswitch: Bridged Azobenzene

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