9 results
Search Results
Now showing 1 - 9 of 9
- ItemEnlightening Materials with Photoswitches(Weinheim : Wiley-VCH, 2020) Goulet-Hanssens, Alexis; Eisenreich, Fabian; Hecht, StefanIncorporating 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 challenges in harnessing geometrical and electronic changes on the molecular level to modulate macroscopic and bulk material properties. Herein, progress made during the past decade in the field of photoswitchable materials is highlighted. After pointing to some general design principles, materials with an increasing order of the integrated photoswitchable units are discussed, spanning the range from amorphous settings over surfaces/interfaces and supramolecular ensembles, to liquid crystalline and crystalline phases. Finally, some potential future directions are pointed out in the conclusion. In view of the exciting recent achievements in the field, the future emergence and further development of light-driven and optically programmable (inter)active materials and systems are eagerly anticipated. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
- ItemImine-Based Dynamic Polymer Networks as Photoprogrammable Amine Sensing Devices(Bognor Regis [u.a.] : Wiley, 2019) Kathan, Michael; Jurissek, Christoph; Kovaříček, Petr; Hecht, StefanHere, we describe a “smart” polymeric material, which is able to readily detect and discriminate amine vapors. The dynamic imine-based network can be conveniently prepared by mixing a commercially available, amino-functionalized polysiloxane with small amounts of a diarylethene dialdehyde. The photoswitchable crosslinker allows for reversible imprinting of custom-designed patterns on the polymer surface with (sun)light and thus enables noninvasive information storage in the material, which before, during, and after amine exposure can readily be decoded with commonly used smartphone apps. This feature along with the self-healing nature of the dynamic polymer, an easy recycling and manufacturing procedure, and the overall low cost and toxicity render this material advantageous to develop low-cost and practical amine sensing devices for the broad public. © 2019 The Authors. Journal of Polymer Science Part A: Polymer Chemistry published by Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2378–2382
- ItemOligothiophene-Based Phosphonates for Surface Modification of Ultraflat Transparent Conductive Oxides(Weinheim : Wiley-VCH, 2020) Timpel, Melanie; Nardi, Marco V.; Wegner, Berthold; Ligorio, Giovanni; Pasquali, Luca; Hildebrandt, Jana; Pätzel, Michael; Hecht, Stefan; Ohta, Hiromichi; Koch, NorbertThe self-assembly of electroactive organic molecules on transparent conductive oxides is a versatile strategy to engineer the interfacial energy-level alignment and to enhance charge carrier injection in optoelectronic devices. Via chemical grafting of an aromatic oligothiophene molecule by changing the position of the phosphonic acid anchoring group with respect to the organic moiety (terminal and internal), the direction of the main molecular dipole is changed, i.e., from parallel to perpendicular to the substrate, to study the molecular arrangement and electronic properties at the organic–inorganic interface. It is found that the observed work function increase cannot solely be predicted based on the calculated molecular dipole moment of the oligothiophene-based phosphonates. In addition, charge transfer from the substrate to the molecule has to be taken into account. Molecular assembly and induced electronic changes are analogous for both indium-tin oxide (ITO) and zinc oxide (ZnO), demonstrating the generality of the approach and highlighting the direct correlation between molecular coverage and electronic effects. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
- ItemMechanistic Insights into the Triplet Sensitized Photochromism of Diarylethenes(Weinheim : Wiley-VCH, 2020) Fredrich, Sebastian; Morack, Tobias; Sliwa, Michel; Hecht, StefanOperating photoswitchable molecules repetitively and reliably is crucial for most of their applications, in particular in (opto)electronic devices, and related to reversibility and fatigue resistance, which both critically depend on the photoisomerization mechanism defined by the substitution pattern. Two diarylethene photoswitches bearing biacetyl triplet sensitizers either at the periphery or at the core were investigated using both stationary as well as transient UV/Vis absorption spectroscopy ranging from the femtosecond to the microsecond time scale. The diarylethene with two biacetyl moieties at the periphery is switching predominantly from the triplet excited state, giving rise to an enhanced fatigue resistance. In contrast, the diarylethene bearing one diketone at the photoreactive inner carbon atom cyclizes from the singlet excited state and shows significantly higher quantum yields for both cyclization and cycloreversion. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
- ItemHighly Cooperative Photoswitching in Dihydropyrene Dimers(Weinheim : Wiley-VCH, 2020) Liesfeld, Pauline; Garmshausen, Yves; Budzak, Simon; Becker, Jonas; Dallmann, Andre; Jacquemin, Denis; Hecht, StefanWe present a strategy to achieve highly cooperative photoswitching, where the initial switching event greatly facilitates subsequent switching of the neighboring unit. By linking donor/acceptor substituted dihydropyrenes via suitable π-conjugated bridges, the quantum yield of the second photochemical ring-opening process could be enhanced by more than two orders of magnitude as compared to the first ring-opening. As a result, the intermediate mixed switching state is not detected during photoisomerization although it is formed during the thermal back reaction. Comparing the switching behavior of various dimers, both experimentally and computationally, helped to unravel the crucial role of the bridging moiety connecting both photochromic units. The presented dihydropyrene dimer serves as model system for longer cooperative switching chains, which, in principle, should enable efficient and directional transfer of information along a molecularly defined path. Moreover, our concept allows to enhance the photosensitivity in oligomeric and polymeric systems and materials thereof. © 2020 The Authors. Published by Wiley-VCH GmbH
- ItemAvoiding the Center-Symmetry Trap: Programmed Assembly of Dipolar Precursors into Porous, Crystalline Molecular Thin Films(Weinheim : Wiley-VCH, 2021) Nefedov, Alexei; Haldar, Ritesh; Xu, Zhiyun; Kühner, Hannes; Hofmann, Dennis; Goll, David; Sapotta, Benedikt; Hecht, Stefan; Krstić, Marjan; Rockstuhl, Carsten; Wenzel, Wolfgang; Bräse, Stefan; Tegeder, Petra; Zojer, Egbert; Wöll, ChristofLiquid-phase, quasi-epitaxial growth is used to stack asymmetric, dipolar organic compounds on inorganic substrates, permitting porous, crystalline molecular materials that lack inversion symmetry. This allows material fabrication with built-in electric fields. A new programmed assembly strategy based on metal-organic frameworks (MOFs) is described that facilitates crystalline, noncentrosymmetric space groups for achiral compounds. Electric fields are integrated into crystalline, porous thin films with an orientation normal to the substrate. Changes in electrostatic potential are detected via core-level shifts of marker atoms on the MOF thin films and agree with theoretical results. The integration of built-in electric fields into organic, crystalline, and porous materials creates possibilities for band structure engineering to control the alignment of electronic levels in organic molecules. Built-in electric fields may also be used to tune the transfer of charges from donors loaded via programmed assembly into MOF pores. Applications include organic electronics, photonics, and nonlinear optics, since the absence of inversion symmetry results in a clear second-harmonic generation signal.
- ItemOptical and chemical control of the wettability of nanoporous photoswitchable films(Cambridge : Royal Society of Chemistry, 2022) Zhang, Zejun; Chen, Donghui; Mutruc, Dragos; Hecht, Stefan; Heinke, LarsWettability is a central surface property of functional thin films. Here, we present a nanoporous film made of an azobenzene-containing metal-organic framework material where the wettability is controlled by photoswitching of the fluorinated azobenzene moieties and by reversible incorporation of guest molecules with different polarities in the pores. Using both, the optical and the chemical stimuli, the water contact angle was modified over a wide range, from 23° to 97°.
- ItemProton-Gated Ring-Closure of a Negative Photochromic Azulene- Based Diarylethene(Weinheim : Wiley-VCH, 2020) Hou, Ian Cheng-Yi; Berger, Fabian; Narita, Akimitsu; Müllen, Klaus; Hecht, StefanProton-responsive photochromic molecules are attractive for their ability to react on non-invasive rapid optical stimuli and the importance of protonation/deprotonation processes in various fields. Conventionally, their acidic/basic sites are on hetero-atoms, which are orthogonal to the photo-active π-center. Here, we incorporate azulene, an acid-sensitive pure hydrocarbon, into the skeleton of a diarylethene-type photoswitch. The latter exhibits a novel proton-gated negative photochromic ring-closure and its optical response upon protonation in both open and closed forms is much more pronounced than those of diarylethene photoswitches with hetero-atom based acidic/basic moieties. The unique behavior of the new photoswitch can be attributed to direct protonation on its π-system, supported by 1H NMR and theoretical calculations. Our results demonstrate the great potential of integrating non-alternant hydrocarbons into photochromic systems for the development of multi-responsive molecular switches. © 2020 The Authors. Published by Wiley-VCH GmbH
- ItemTunable Photomechanics in Diarylethene-Driven Liquid Crystal Network Actuators(Washington, DC : ACS Publications, 2020) Lahikainen, Markus; Kuntze, Kim; Zeng, Hao; Helantera, Seidi; Hecht, Stefan; Priimagi, ArriThe response of soft actuators made of stimuli-responsive materials can be phenomenologically described by a stimulus-deformation curve, depicting the controllability and sensitivity of the actuator system. Manipulating such stimulus-deformation curve allows fabricating soft microrobots with reconfigurable actuation behavior, which is not easily achievable using conventional materials. Here, we report a light-driven actuator based on a liquid crystal polymer network containing diarylethene (DAE) photoswitches as cross-links, in which the stimulus-deformation curve under visible-light illumination is tuned with UV light. The tuning is brought about by the reversible electrocyclization of the DAE units. Because of the excellent thermal stability of the visible-absorbing closed-form DAEs, the absorbance of the actuator can be optically fixed to a desired value, which in turn dictates the efficiency of photothermally induced deformation. We employ the controllability in devising a logical AND gate with macroscopic output, i.e., an actuator that bends negligibly under UV or visible light irradiation, but with profound shape change when addressed to both simultaneously. The results provide design tools for reconfigurable microrobotics and polymer-based logic gating. © 2020 American Chemical Society. All rights reserved.