Electronic Properties of Optically Switchable Photochromic Diarylethene Molecules at the Interface with Organic Semiconductors

Wang, Qiankun; Frisch, Johannes; Herder, Martin; Hecht, Stefan; Koch, Norbert

doi:10.1002/cphc.201601442

Cited by 24 publications

(33 citation statements)

References 31 publications

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“…Both the ability to chemically tune the energy levels through chemical substitution as well as the orientation of the DAE molecules with regard to the surface were found to have a large effect on the work function of the surface . In addition to thin films, also SAMs have been used to modulate charge injection barriers. Incorporating thiol anchoring groups into the structure of DAEs was used to prepare SAMs on a gold electrode, which allowed for switching of device characteristics by light when applied in an organic thin‐film transistor (OTFT) .…”

Section: Photoswitches On Surfacesmentioning

confidence: 99%

Enlightening Materials with Photoswitches

2020

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reversible conversion between their stable and (meta)stable isomers triggered by light. The return to their native, thermo dynamically most stable isomer is gener ally induced by using another wavelength of light or simply by heat, depending on the thermal stability of the (meta)stable isomer. Retinal-the prototypical photo switch in biology-showcases impressively how structural changes occurring during a lightinduced doublebond isomerization can lead to vision or allow microorganisms to convert photons into metabolic energy. In analogy, over the years, scientists have learned that the lightdriven isomeriza tion of small molecules can be collected, possibly amplified, and transformed into macroscopic property changes, such as mechanical motion, [1] charge carrying ability, [2] assembly and disassembly of macroscopic aggregates, [3] as well as switching of surfaces and their properties. [4] Materials, which for the purpose of this review are consid ered to be solid objects or organized assemblies in solution, provide unique advantages to enhance the function of photo switches and even create new functions when compared to their standalone molecular selves (for the primarily discussed photochromic molecules herein, see Figure 1). One must, how ever, consider the inherent challenges that may present them selves when working with photoswitches in close proximity to one another. Intermolecular interactions, such as aggregation, excitation quenching, low freevolume, as well as the poten tially much higher optical density of materials can drastically lower the overall photoresponse. Yet with proper macromo lecular and supramolecular design, functions can be achieved through the incorporation of photoswitches in a material that simply cannot be obtained by an isolated molecule on its own. Here, we highlight recent examples from the literature that have appeared during the past decade since our previous review in this journal, [5] with particular focus on the order of the photos witches in relation to their environment and its impact on mate rial properties and device performance.Conceptually, one can think about maximizing a photo switching unit's effect by giving it "order" with relation to its surrounding, in particular to other switching units (Figure 2). The lowest possible order is undoubtedly demonstrated by dis persing photochromic molecules in a bulk amorphous material. If aggregation of the photoswitches can be overcome, switching units are placed in random orientation to each other giving rise to a more or less isotropic material. Starting from this scenario of randomly distributed photochromic entities, one can think about providing order in two dimensions by placing Incorporating molecular photoswitches into various materials provides unique opportunities for controlling their properties and functions with high spatiotemporal resolution using remote optical stimuli. The great and largely still untapped potential of these photoresponsive systems has not yet been fully exploited due to the fundamental challenge...

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Section: Photoswitches On Surfacesmentioning

confidence: 99%

Enlightening Materials with Photoswitches

2020

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“…Thus, the ring opening induced gap renormalization places the HOMO level onset 0.7 eV farther away from EF, in line with qualitatively similar observations made for other photo-switches. [11] Next, the sample was heated in situ to a temperature of 50 ºC for 30 min in order to induce the reverse ring- To study how switching of Py-DHP in thicker films impacts the interface electronic properties, we first increased the organic layer thickness to nominally 50 Å (see Figure S2), and subsequently to 100 Å on both ZnO surfaces. We observe that the HOMO onset of the closed Py-DHP thick films is still at 1.8 eV, where it was also found for the monolayer.…”

Section: Switching Properties Of Py-dhpmentioning

confidence: 99%

“…[6,9] However, this approach is limited to a static modification of the energy levels at the interface. More recently, the use of molecular switches has been shown to enable a dynamic energy level tuning, [11][12][13] which gives the interface multifunctional properties since the energy level alignment can be controlled and programmed via external stimuli, even in fully processed and encapsulated device stacks.…”

Section: Introductionmentioning

confidence: 99%

“…These molecular compounds can be reversibly switched between two isomers by external stimuli, such as light, heat, and pH changes. [14,15] The switching between the two isomers fundamentally changes the electronic properties of the molecular compound, e.g., the energy gap, the ionization energy and electron affinity, the molecular dipole moment, [11] as well as carrier mobility in blends with other organic semiconductors. [16,17] Thus, once the molecular switch is combined with other materials, the isomerization results in dynamically controlled hetero-interfaces as well as bulk semiconductor properties.…”

Section: Introductionmentioning

confidence: 99%

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Switching the Electronic Properties of ZnO Surfaces with Negative T‐Type Photochromic Pyridyl‐dihydropyrene Layers and Impact of Fermi Level Pinning

Wang

Ligorio

Schlesinger

et al. 2019

Adv Materials Inter

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Remote control of the electronic energy levels by external stimuli such as light will enable optoelectronic devices with improved or additional functionalities. Here, we demonstrate that the electronic properties of ZnO interfaced with molecular negative T-type photoswitches, i.e., pyridyl-dihydropyrene (Py-DHP), can indeed be photomodulated. The process of forward switching of Py-DHP with green light from an isomer with a low energy gap to an isomer with a wider one is followed by a thermally activated backward transfer.This process is found to be fully reversible and efficient in the solid state. Using photoemission spectroscopy and density functional theory (DFT) modelling, we show that the photochromic ring closure/opening process results in reversible shift of the frontier occupied molecular level by 0.7 eV with respect to the Fermi level. Notably, in both molecular configurations, the energy level alignment at the ZnO/Py-DHP interface is governed by a Fermi level pinning of the lowest unoccupied molecular level. Moreover, upon switching, we observe an increase in the ionization energy for Py-DHP multilayers compared to that of a monolayer. We attribute this to a different preferred molecular orientation in monolayer versus multilayer films. Our results show that dynamic tuning of the interface energy level alignment at inorganic/organic junctions by external stimuli is feasible and will aid the development of photoprogrammable opto-electronic devices.

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“…In this context, photochromic molecules are ideal candidates, as light constitutes a fast, non-invasive and low-cost trigger to remotely control the state of the system [2]. Notably, embedding photochromic SAMs in organic or hybrid field-effect transistors opens the way for the fine-tuning of both morphological and electronic properties of the interfaces at stake in the overall response of the device [3][4][5][6]. In the current library of photoswitches, azobenzene derivatives, which exhibit a reversible light-triggered isomerization between a stable trans and a metastable cis state, stand as the most commonly used [7][8][9][10][11][12][13][14][15].…”

Section: Introductionmentioning

confidence: 99%

Atomistic simulations of charge transport in photoswitchable organic-graphene hybrids

et al. 2019

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Photoswitchable self-assembled monolayers (SAMs) in contact with a conductive or semiconductive layer can be used to remotely trigger changes in electrical current using light. In this study, we apply full-atomistic simulations to assess the changes in electronic structure and charge-transport properties of a graphene sheet in contact with an amorphous silica dielectric decorated by an azobenzene SAM. The simulations explicitly account for the structural and electrostatic disorder sourced by the dielectric, which turns out to be weakly affected by photoisomerization and spatially correlated over a length scale of 4-5 nm. Most interestingly, by combining large-scale (tight binding) density functional theory with Kubo-Greenwood quantum transport calculations, we predict that the trans-cis isomerization should induce a shift in surface electrostatic potential by a few tenths of a volt, accompanied by a variation in conductivity by a factor of about 3.

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Electronic Properties of Optically Switchable Photochromic Diarylethene Molecules at the Interface with Organic Semiconductors

Cited by 24 publications

References 31 publications

Enlightening Materials with Photoswitches

Enlightening Materials with Photoswitches

Switching the Electronic Properties of ZnO Surfaces with Negative T‐Type Photochromic Pyridyl‐dihydropyrene Layers and Impact of Fermi Level Pinning

Atomistic simulations of charge transport in photoswitchable organic-graphene hybrids

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