9 research outputs found
Sunlight-powered kHz rotation of a hemithioindigo-based molecular motor
Photodriven molecular motors are able to convert light energy into directional motion and hold great promise as miniaturized powering units for future nanomachines. In the current state of the art, considerable efforts have still to be made to increase the efficiency of energy transduction and devise systems that allow operation in ambient and non-damaging conditions with high rates of directional motions. The need for ultraviolet light to induce the motion of virtually all available light-driven motors especially hampers the broad applicability of these systems. We describe here a hemithioindigo-based molecular motor, which is powered exclusively by nondestructive visible light (up to 500 nm) and rotates completely directionally with kHz frequency at 20 degrees C. This is the fastest directional motion of a synthetic system driven by visible light to date permitting materials and biocompatible irradiation conditions to establish similarly high speeds as natural molecular motors
Direct evidence for hula twist and single-bond rotation photoproducts
Photoisomerization reactions are quintessential processes driving molecular machines and motors, govern smart materials, catalytic processes, and photopharmacology, and lie at the heart of vision, phototaxis, or vitamin production. Despite this plethora of applications fundamental photoisomerization mechanisms are not well understood at present. The famous hula-twist motion-a coupled single and double-bond rotation-was proposed to explain proficient photoswitching in restricted environments but fast thermal follow-up reactions hamper identification of primary photo products. Herein we describe an asymmetric chromophore possessing four geometrically distinct diastereomeric states that do not inter-convert thermally and can be crystallized separately. Employing this molecular setup direct and unequivocal evidence for the hula-twist photoreaction and for photoinduced single-bond rotation is obtained. The influences of the surrounding medium and temperature are quantified and used to favor unusual photoreactions. Based on our findings molecular engineers will be able to implement photo control of complex molecular motions more consciously
Sunlight-powered kHz rotation of a hemithioindigo-based molecular motor
Photodriven molecular motors are able to convert light energy into directional motion and hold great promise as miniaturized powering units for future nanomachines. In the current state of the art, considerable efforts have still to be made to increase the efficiency of energy transduction and devise systems that allow operation in ambient and non-damaging conditions with high rates of directional motions. The need for ultraviolet light to induce the motion of virtually all available light-driven motors especially hampers the broad applicability of these systems. We describe here a hemithioindigo-based molecular motor, which is powered exclusively by nondestructive visible light (up to 500 nm) and rotates completely directionally with kHz frequency at 20 degrees C. This is the fastest directional motion of a synthetic system driven by visible light to date permitting materials and biocompatible irradiation conditions to establish similarly high speeds as natural molecular motors
Oxidized Hemithioindigo Photoswitches-Influence of Oxidation State on (Photo)physical and Photochemical Properties
The photophysical and photochemical properties of sulfoxide and sulfone derivatives of hemithioindigo photoswitches are scrutinized and compared to the unoxidized parent chromophores. Oxidation results in significantly blue-shifted absorptions and mostly reduction of photochromism while thermal stabilities of individual isomers remain largely unaltered. Effective photoswitching takes place at shorter wavelengths compared to parent hemithioindigos and high isomeric yields can be obtained reversibly in the respective photostationary states. Reversible solid-state photoswitching is observed for a twisted sulfone derivative accompanied by visible color changes. These results establish oxidized hemithioindigo photoswitches as promising and versatile tools for robust light-control of molecular behavior for a wide range of applications
Umgang mit lernungewohnten Teilnehmern mit z.T. fossilisierten Sprachbeständen auf niedrigem Niveau. Portfolioarbeit in Förderkursen
David M, Maslach J. Umgang mit lernungewohnten Teilnehmern mit z.T. fossilisierten Sprachbeständen auf niedrigem Niveau. Portfolioarbeit in Förderkursen. In: Ammermann A, Brock A, Pflaeging J, Schildhauer P, eds. Facets of Linguistics. Proceedings of the 14th Norddeutsches Linguistisches Kolloquium 2013 in Halle (Saale). Frankfurt am Main: Peter Lang; 2013: 133-145
Oxidized Hemithioindigo Photoswitches—Influence of Oxidation State on (Photo)physical and Photochemical Properties
The photophysical and photochemical properties of sulfoxide and sulfone derivatives of hemithioindigo photoswitches are scrutinized and compared to the unoxidized parent chromophores. Oxidation results in significantly blue-shifted absorptions and mostly reduction of photochromism while thermal stabilities of individual isomers remain largely unaltered. Effective photoswitching takes place at shorter wavelengths compared to parent hemithioindigos and high isomeric yields can be obtained reversibly in the respective photostationary states. Reversible solid-state photoswitching is observed for a twisted sulfone derivative accompanied by visible color changes. These results establish oxidized hemithioindigo photoswitches as promising and versatile tools for robust light-control of molecular behavior for a wide range of applications
Complete Mechanism of Hemithioindigo Motor Rotation
Hemithioindigo-based molecular motors
are powered by nondamaging
visible light and provide very fast directional rotations at ambient
conditions. Their ground state energy profile has been probed in detail,
but the crucial excited state processes are completely unknown so
far. In addition, very fast processes in the ground state are also
still elusive to date and thus knowledge of the whole operational
mechanism remains to a large extent in the dark. In this work we elucidate
the complete light-driven rotation mechanism by a combination of multiscale
broadband transient absorption measurements covering a time scale
from fs to ms in conjunction with a high level theoretical description
of the excited state. In addition to a full description of the excited
state dynamics in the various time regimes, we also provide the first
experimental evidence for the elusive fourth intermediate ground state
of the original HTI motor. The fate of this intermediate also is followed
directly proving complete unidirectionality for both 180° rotation
steps. At the same time, we uncover the hitherto unknown involvement
of an unproductive triplet state pathway, which slightly diminishes
the quantum yield of the <i>E</i> to <i>Z</i> photoisomerization.
A rate model analysis shows that increasing the speed of motor rotation
is most effectively done by increasing the photoisomerization quantum
yields instead of barrier reduction for the thermal ratcheting steps.
Our findings are of crucial importance for improved future designs
of any light-driven molecular motor in general to yield better efficiencies
and applicability