1
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Gain of Function Recyclable Photoswitches: Reversible Simultaneous Substitution and Photochromism Generation. Angew Chem Int Ed Engl 2024; 63:e202318767. [PMID: 38315498 DOI: 10.1002/anie.202318767] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2023] [Revised: 01/20/2024] [Accepted: 01/23/2024] [Indexed: 02/07/2024]
Abstract
The use of molecular photoswitches has spread to virtually every field of pure and applied chemistry because of the extraordinary level of control they provide over the behavior of matter at the smallest scales. Photoswitches possess at least two different states with distinct structures and/or electronics and further functionalization of their core chromophore structures is needed to tailor them for a specific application. In this work we present a different concept for the generation and use of molecular photoswitches. It allows not only simultaneous establishment of photochromism and functionalization, but also full recyclability of a non-photochromic precursor material. Using a high-yielding and reversible ammonium salt formation, a functional group is introduced into a symmetric precursor while at the same time a strong electronic push-pull character is established in the structure. The resulting desymmetrization leads to efficient photoswitching capacity and the functional group can be fully removed subsequently by a simple heating step recovering the precursor for another functionalization round. We finally demonstrate feasibility of this concept over two consecutive closed loop functionalization/photoswitching/recovery steps. This concept offers great potential in any chemical research and application driven area but especially for the creation of responsive reprogrammable materials, no-background photoswitch labeling, and sustainable chemistry.
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2
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Reversible C═N Bond Formation Controls Charge-Separation in an Aza-Diarylethene Photoswitch. J Am Chem Soc 2024; 146:9575-9582. [PMID: 38536769 DOI: 10.1021/jacs.3c11803] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/11/2024]
Abstract
Diarylethenes belong to the most eminent photoswitches and have been studied for many decades. They are found in virtually every field of application and have become highly valuable molecular tools for instilling light-responsiveness into materials, catalysts, biological systems, or pharmacology. In this work, we present a novel and distinct type of pyrimidine-based aza-diarylethene, which undergoes a highly unusual zwitterion-forming photoreaction. During this fully reversible process, a CN double bond is established under concomitant aromatization and thiophene-ring opening. The metastable zwitterion thus possesses a positively charged extended aromatic structure and an independent conjugated thiolate function. It can further photoisomerize between a more stable Z and a less stable E isomer, resulting in effective four-state photoswitching. Unusual for diarylethenes, the metastable isomers show negative solvatochromism and red-shifted absorption in apolar solvents. With this behavior, aza-diarylethenes effectively bridge the properties of merocyanines and diarylethenes. Thermal stability of the zwitterions can be modulated from very labile to highly stable behavior in response to pH, again in a fully reversible manner. Pyrimidine-based aza-diarylethene thus establishes a unique photoreaction mechanism for diarylethenes, allowing control of charge separation, thermal stability, and color generation in a different way than hitherto possible.
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3
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Maximizing Performance and Stability of Organic Solar Cells at Low Driving Force for Charge Separation. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2024; 11:e2305948. [PMID: 38039433 PMCID: PMC10853714 DOI: 10.1002/advs.202305948] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/22/2023] [Revised: 10/19/2023] [Indexed: 12/03/2023]
Abstract
Thanks to the development of novel electron acceptor materials, the power conversion efficiencies (PCE) of organic photovoltaic (OPV) devices are now approaching 20%. Further improvement of PCE is complicated by the need for a driving force to split strongly bound excitons into free charges, causing voltage losses. This review discusses recent approaches to finding efficient OPV systems with minimal driving force, combining near unity quantum efficiency (maximum short circuit currents) with optimal energy efficiency (maximum open circuit voltages). The authors discuss apparently contradicting results on the amount of exciton binding in recent literature, and approaches to harmonize the findings. A comprehensive view is then presented on motifs providing a driving force for charge separation, namely hybridization at the donor:acceptor interface and polarization effects in the bulk, of which quadrupole moments (electrostatics) play a leading role. Apart from controlling the energies of the involved states, these motifs also control the dynamics of recombination processes, which are essential to avoid voltage and fill factor losses. Importantly, all motifs are shown to depend on both molecular structure and process conditions. The resulting high dimensional search space advocates for high throughput (HT) workflows. The final part of the review presents recent HT studies finding consolidated structure-property relationships in OPV films and devices from various deposition methods, from research to industrial upscaling.
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4
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Azotriptycenes: Photoswitchable Molecular Brakes. Chemistry 2024; 30:e202302267. [PMID: 37779321 DOI: 10.1002/chem.202302267] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2023] [Revised: 09/24/2023] [Accepted: 09/27/2023] [Indexed: 10/03/2023]
Abstract
The control of molecular motions is a central topic of molecular machine research. Molecular brakes are fundamental building blocks towards such goal as they allow deliberately decelerating specific motions after an outside stimulus is applied. Here we present azotriptycenes as structural framework for light-controlled molecular brakes. The intrinsic kinetics and their changes upon azotriptycene isomerization are scrutinized comprehensively by a mixed theoretical and variable temperature NMR approach. With azotriptycenes C-N bond rotation rates can be decelerated or accelerated reversibly by up to five orders of magnitude. Rate change effects are highly localized and are strongest for the C-N bond connecting a triptycene rotor fragment to the central diazo group. The detailed mechanistic insights provide a solid basis for further conscious design and applications in the future.
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5
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Rhodanine-Based Chromophores: Fast Access to Capable Photoswitches and Application in Light-Induced Apoptosis. J Am Chem Soc 2024; 146:1894-1903. [PMID: 38207286 DOI: 10.1021/jacs.3c07710] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2024]
Abstract
Molecular photoswitches are highly desirable in all chemistry-related areas of research. They provide effective outside control over geometric and electronic changes at the nanoscale using an easy to apply, waste-free stimulus. However, simple and effective access to such molecular tools is typically not granted, and elaborate syntheses and substitution schemes are needed in order to obtain efficient photoswitching properties. Here we present a series of rhodanine-based photoswitches that can be prepared in one simple synthetic step without requiring elaborate purification. Photoswitching is induced by UV and visible light in both switching directions, and thermal stabilities of the metastable states as well as quantum yields are very high. An additional benefit is the hydrogen-bonding capacity of the rhodanine fragment, which enables applications in supramolecular or medicinal chemistry. We further show that the known rhodanine-based inhibitor SMI-16a is a photoswitchable apoptosis inducer. The biological activity of SMI-16a can effectively be switched ON or OFF by reversible photoisomerization between the inactive E and the active Z isomer. Rhodanine-based photoswitches therefore represent an easy to access and highly valuable molecular toolbox for implementing light responsiveness to the breadth of functional molecular systems.
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6
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Peri-Anthracenethioindigo: A Scaffold for Efficient All-Red-Light and Near-Infrared Molecular Photoswitching. Angew Chem Int Ed Engl 2023; 62:e202312955. [PMID: 37806956 DOI: 10.1002/anie.202312955] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2023] [Revised: 10/04/2023] [Accepted: 10/05/2023] [Indexed: 10/10/2023]
Abstract
Molecular photoswitching with red light is greatly desired to evade photodamage and achieve specific photoresponses. In virtually all reported cases however, only one switching direction uses red light while for the reverse switching, UV or visible light is needed. All-red-light photoswitching brings with it the clear advantage of pushing photoswitching to the limit of the low-energy spectrum, but no viable system is available currently. Here we report on peri-anthracenethioindigo (PAT) as molecular scaffold for highly efficient all-red-light photoswitching with an outstanding performance and property profile. The PAT photoswitch provides near-infrared (NIR) absorption up to 850 nm, large negative photochromism with more than 140 nm maxima shifts and changes color from green to blue upon irradiation with two shades of red light. Thermal stability of the metastable Z isomer is high with a corresponding half-life of days at 20 °C. Application in red-light responsive polymers undergoing pronounced and reversible green to blue color changes demonstrate spatially resolved photoswitching. The PAT photoswitch thus offers unique responsiveness to very low energy light together with predictable and large geometrical changes within a rigid molecular scaffold. We expect a plethora of applications for PAT in the near future, e.g. in materials, molecular machines or biological context.
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7
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A photochemical method to evidence directional molecular motions. Nat Commun 2023; 14:4595. [PMID: 37524701 PMCID: PMC10390485 DOI: 10.1038/s41467-023-40190-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2022] [Accepted: 07/17/2023] [Indexed: 08/02/2023] Open
Abstract
Light driven synthetic molecular motors represent crucial building blocks for advanced molecular machines and their applications. A standing challenge is the development of very fast molecular motors able to perform rotations with kHz, MHz or even faster frequencies. Central to this challenge is the direct experimental evidence of directionality because analytical methods able to follow very fast motions rarely deliver precise geometrical insights. Here, a general photochemical method for elucidation of directional motions is presented. In a macrocyclization approach the molecular motor rotations are restricted and forced to proceed in two separate ~180° rotation-photoequilibria. Therefore, all four possible photoinduced rotation steps (clockwise and counterclockwise directions) can be quantified. Comparison of the corresponding quantum yields to the unrestricted motor delivers direct evidence for unidirectionality. This method can be used for any ultrafast molecular motor even in cases where no high energy intermediates are present during the rotation cycle.
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8
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Diaryl-hemiindigos as visible light, pH, and heat responsive four-state switches and application in photochromic transparent polymers. Nat Commun 2023; 14:4382. [PMID: 37474507 PMCID: PMC10359318 DOI: 10.1038/s41467-023-39944-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2022] [Accepted: 06/14/2023] [Indexed: 07/22/2023] Open
Abstract
Photoswitches are indispensable tools for responsive chemical nanosystems and are used today in almost all areas of the natural sciences. Hemiindigo (HI) derivatives have recently been introduced as potent photoswitches, but their full applicability has been hampered by the limited possibilities of their functionalization and structural modification. Here we report on a short and easy to diversify synthesis yielding diaryl-HIs bearing one additional aromatic residue at the central double bond. The resulting chromophores offer an advantageous property profile combining red-light responsiveness, high thermal bistability, strong isomer accumulations in both switching directions, strong photochromism, tunable acid responsiveness, and acid gating. With this progress, a broader structural realm becomes accessible for HI photoswitches, which can now be synthetically tailored for advanced future applications, e.g., in research on molecular machines and switches, in studies of photoisomerization mechanisms, or in the generation of smart and addressable materials. To showcase the potential of these distinct light-responsive molecular tools, we demonstrate four-state switching, chemical fueling, and reversible inscription into transparent polymers using green and red light as well as acid/base stimuli, in addition to a comprehensive photochemical study of all compounds.
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9
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Mechanistic Elucidation of the Hula-Twist Photoreaction in Hemithioindigo. J Am Chem Soc 2023. [PMID: 37364887 DOI: 10.1021/jacs.3c03536] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/28/2023]
Abstract
The Hula-Twist (HT) photoreaction represents a fundamental photochemical pathway for bond isomerizations and is defined by the coupled motion of a double bond and an adjacent single bond. This photoreaction has been suggested as the defining motion for a plethora of light-responsive chromophores such as retinal within opsins, coumaric acid within photoactive yellow protein, or vitamin D precursors, and stilbenes in solution. However, due to the fleeting character of HT photoproducts a direct experimental observation of this coupled molecular motion was severely hampered until recently. To solve this dilemma, the Dube group has designed a molecular framework able to deliver unambiguous experimental evidence of the HT photoreaction. Using sterically crowded atropisomeric hemithioindigo (HTI) the HT photoproducts are rendered thermally stable and can be observed directly after their formation. However, following the ultrafast excited state process of the HT photoreaction itself has not been achieved so far and thus crucial information for an elementary understanding is still missing. In this work, we present the first ultrafast spectroscopy study of the HT photoreaction in HTI and probe the competition between different excited state processes. Together with extensive excited state calculations a detailed mechanistic picture is developed explaining the significant solvent effects on the HT photoreaction and revealing the intricate interplay between productive isomerizations and unproductive twisted intramolecular charge transfer (TICT) processes. With this study essential insights are thus gained into the mechanism of complex multibond rotations in the excited state, which will be of primary importance for further developments in this field.
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10
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Defining Unidirectional Motions and Structural Reconfiguration in a Macrocyclic Molecular Motor. J Am Chem Soc 2023. [PMID: 37279894 DOI: 10.1021/jacs.3c01567] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The construction of sophisticated molecular machines requires not only precise control of energy fueled motions but their integration into larger functional architectures. Macrocyclization of molecular motors is a way to harness the intrinsic directionality of their rotation and use them to actively power different processes at the nano-scale. An effective concept in this regard uses a defined fragment of the molecular motor as a revolving door within the macrocycle. In this way, motor motions can be transmitted to distant structural entities, other rotations can be actively accelerated, or mechanical molecular threading events can be realized. In this work, a dual macrocyclization approach is presented, which not only allows to supersize the revolving door element but also structurally reconfigure the macrocycle in which the revolving door rotates. Unique possibilities for a multi-level precision control over integrated directional motions are thus opened up without deteriorating the functionality of the molecular machine.
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11
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A cross-conjugation approach for high-performance diaryl-hemithioindigo photoswitches. Chem Sci 2023; 14:5734-5742. [PMID: 37265733 PMCID: PMC10231315 DOI: 10.1039/d2sc06939c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2022] [Accepted: 04/28/2023] [Indexed: 06/03/2023] Open
Abstract
Diaryl-hemithioindigos (diaryl-HTIs) are derivatives of a novel class of highly functionalized indigoid chromophores. In this work a systematic study of the electronic effects on their photoswitching reveals the design principles for achieving an excellent property profile. Two key elements need to be invoked for perfect diaryl-HTI performance, first introduction of strong electron donors and second establishment of cross-conjugation. The resulting photoswitches combine high thermal stability, large extinction coefficients, red-light responsiveness, pronounced photochromism, and strong isomer accumulation in the photostationary states with precise geometry changes. By using the inherent basicity of their strong electron donor moiety, diaryl-HTIs can be rendered into very potent tools for molecular logic applications. We demonstrate a variety of binary logic setups as well as sophisticated three- and four-input keypad locks for sequential logic operations. Three distinct states and up to four different stimuli are invoked for this multi-level molecular information processing. Diaryl-HTIs have thus entered the stage as very capable and promising photoswitch motives for anyone interested in reversible visible- and red-light as well as multi-stimuli responsive molecular behavior.
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12
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Heterocyclic Hemithioindigos: Highly Advantageous Properties as Molecular Photoswitches. Angew Chem Int Ed Engl 2022; 61:e202210855. [PMID: 36040861 PMCID: PMC9826360 DOI: 10.1002/anie.202210855] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2022] [Indexed: 01/11/2023]
Abstract
A survey of heterocyclic hemithioindigo photoswitches is presented identifying a number of structural motives with outstanding property profiles. The highly sought-after combination of pronounced color change, quantitative switching in both directions, exceptional high quantum yields, and tunable high thermal stability of metastable states can be realized with 4-imidazole, 2-pyrrole, and 3-indole-based derivatives. In the former, an unusual preorganization using isomer selective chalcogen- and hydrogen bonding allows to precisely control geometry changes and tautomerism upon switching. Heterocyclic hemithioindigos thus represent highly promising photoswitches with advanced capabilities that will be of great value to anyone interested in establishing defined and reversible control at the molecular level.
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13
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Heterocyclic Hemithioindigos: Highly Advantageous Properties as Molecular Photoswitches. Angew Chem Int Ed Engl 2022. [DOI: 10.1002/ange.202210855] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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14
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Inside Cover: Active Mechanical Threading by a Molecular Motor (Angew. Chem. Int. Ed. 19/2022). Angew Chem Int Ed Engl 2022. [DOI: 10.1002/anie.202204177] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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15
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Abstract
Molecular motors transform external energy input into directional motions and offer exquisite precision for nano‐scale manipulations. To make full use of molecular motor capacities, their directional motions need to be transmitted and used for powering downstream molecular events. Here we present a macrocyclic molecular motor structure able to perform repetitive molecular threading of a flexible tetraethylene glycol chain through the macrocycle. This mechanical threading event is actively powered by the motor and leads to a direct translation of the unidirectional motor rotation into unidirectional translation motion (chain versus ring). The mechanism of the active mechanical threading is elucidated and the actual threading step is identified as a combined helix inversion and threading event. The established molecular machine function resembles the crucial step of macroscopic weaving or sewing processes and therefore offers a first entry point to a “molecular knitting” counterpart.
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16
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Innentitelbild: Active Mechanical Threading by a Molecular Motor (Angew. Chem. 19/2022). Angew Chem Int Ed Engl 2022. [DOI: 10.1002/ange.202204177] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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17
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An Eight-State Molecular Sequential Switch Featuring a Dual Single-Bond Rotation Photoreaction. J Am Chem Soc 2022; 144:3029-3038. [PMID: 35157802 PMCID: PMC8874910 DOI: 10.1021/jacs.1c11183] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
![]()
Typical photoswitches
interconvert between two different states
by simple isomerization reactions, which represents a fundamental
limit for applications. To expand the switching capacity usually different
photoswitches have to be linked together leading to strong increase
in molecular weight, diminished switching function, and less precision
and selectivity of switching events. Herein we present an approach
for solving this essential problem with a different photoswitching
concept. A basic molecular switch architecture provides precision
photoswitching between eight different states via controlled rotations
around three adjacent covalent bonds. All eight states can be populated
one after another in an eight-step cycle by alternating between photochemical
Hula-Twist isomerizations and thermal single-bond rotations. By simply
changing solvent and temperature the same switch can also undergo
a different cycle instead interconverting just five isomers in a selective
sequence. This behavior is enabled through the discovery of an unprecedented
photoreaction, a one-photon dual single-bond rotation.
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18
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Hemithioindigo-Based Trioxobicyclononadiene: 3D Multiswitching of Electronic and Geometric Properties. J Am Chem Soc 2022; 144:2847-2852. [PMID: 35157795 PMCID: PMC8874893 DOI: 10.1021/jacs.1c12364] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
![]()
Molecular photoswitches
that offer simultaneous precise control
over geometrical and electronic changes are rare yet highly sought
tools for the development of responsive nanosystems. Here we present
such an advantageous combination of property control within a novel
multiphotoswitch architecture. Hemithioindigo-based trioxobicyclononadiene
(HTI-TOND) offers a rigid three-dimensional molecular structure that
undergoes different exotic rearrangement reactions upon photochemical
and thermal signaling. Three to four different states with distinct
geometric and electronic properties can be accessed reversibly in
high yields within this molecular framework. Thus, a highly promising
and unique switching tool has become available to instill the next
level of addressability at the smallest scales.
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19
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Active Mechanical Threading by a Molecular Motor. Angew Chem Int Ed Engl 2022. [DOI: 10.1002/ange.202201882] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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20
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Quantitative
In‐Situ
NMR Illumination for Excitation and Kinetic Analysis of Molecular Motor Intermediates. CHEMPHOTOCHEM 2022. [DOI: 10.1002/cptc.202200018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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21
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Quantitative
In‐Situ
NMR Illumination for Excitation and Kinetic Analysis of Molecular Motor Intermediates. CHEMPHOTOCHEM 2022. [DOI: 10.1002/cptc.202200019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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22
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Quantitative
In‐Situ
NMR Illumination for Excitation and Kinetic Analysis of Molecular Motor Intermediates. CHEMPHOTOCHEM 2022. [DOI: 10.1002/cptc.202100232] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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23
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Abstract
![]()
Red-light responsiveness
of photoswitches is a highly desired property
for many important application areas such as biology or material sciences.
The main approach to elicit this property uses strategic substitution
of long-known photoswitch motives such as azobenzenes or diarylethenes.
Only very few photoswitches possess inherent red-light absorption
of their core chromophore structures. Here, we present a strategy
to convert the long-known purple indirubin dye into a prolific red-light-responsive
photoswitch. In a supramolecular approach, its photochromism can be
changed from a negative to a positive one, while at the same time,
significantly higher yields of the metastable E-isomer
are obtained upon irradiation. E- to Z-photoisomerization can then also be induced by red light of longer
wavelengths. Indirubin therefore represents a unique example of reversible
photoswitching using entirely red light for both switching directions.
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24
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Abstract
Tuning the thermal behavior of light driven molecular motors is fundamentally important for their future rational design. In many molecular motors thermal ratcheting steps are comprised of helicity inversions, energetically stabilizing the initial photoproducts. In this work we investigated a series of five hemithioindigo (HTI) based molecular motors to reveal the influence of steric hindrance in close proximity to the rotation axle on this process. Applying a high yielding synthetic procedure, we synthesized constitutional isomeric derivatives to distinguish between substitution effects at the aromatic and aliphatic position on the rotor fragment. The kinetics of thermal helix inversions were elucidated using low temperature 1 H NMR spectroscopy and an in situ irradiation technique. In combination with a detailed theoretical description, a comparative analysis of substituent effects on the thermal helix inversions of the rotation cycle is now possible. Such deeper understanding of the rotational cycle of HTI molecular motors is essential for speed regulation and future applications of visible light triggered nanomachines.
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25
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Electronic and Geometric Characterization of TICT Formation in Hemithioindigo Photoswitches by Picosecond Infrared Spectroscopy. J Phys Chem A 2021; 125:4390-4400. [PMID: 33989005 DOI: 10.1021/acs.jpca.1c02646] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Deciphering the exact electronic and geometric changes of photoexcited molecules is an important task not only to understand the fundamental atomistic mechanisms but also to rationally design molecular properties and functions. Here, we present a combined experimental and theoretical study of the twisted intramolecular charge transfer (TICT) process in hemithioindigo photoswitches. Using ultrafast transient IR spectroscopy as the main analytical method, a detailed understanding of the extent and direction of charge transfer within the excited molecule is obtained. At the same time, the geometrical distortion is monitored directly via changes of indicative vibrational modes over the time course of the photoreaction. These high-resolution data deliver a detailed molecular movie of the TICT process in this important class of chromophores with picosecond time resolution.
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26
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Corrigendum: Active and Unidirectional Acceleration of Biaryl Rotation by a Molecular Motor. Angew Chem Int Ed Engl 2021; 60:7473. [PMID: 33751784 DOI: 10.1002/anie.202101793] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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27
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Berichtigung: Active and Unidirectional Acceleration of Biaryl Rotation by a Molecular Motor. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202101793] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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28
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Innentitelbild: Light‐Controlled Cell‐Cycle Arrest and Apoptosis (Angew. Chem. 3/2021). Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202014393] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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29
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Inside Cover: Light‐Controlled Cell‐Cycle Arrest and Apoptosis (Angew. Chem. Int. Ed. 3/2021). Angew Chem Int Ed Engl 2021. [DOI: 10.1002/anie.202014393] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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30
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Abstract
Introducing responsive elements into supramolecular recognition systems offers great advantages for the control of intermolecular interactions and represents an important stepping stone towards multi-purpose and reprogrammable synthetic systems. Of particular interest is implementation of light-responsiveness because of the unique ease and precision of this signal. Here we present visible light responsive hemithioindigo-based molecular tweezers that bear a highly polar sulfoxide function as an additional recognition unit inside their binding site. Sulfur oxidation allows to simultaneously enhance all crucial properties of this receptor type i.e. photoswitching capability, thermal stability of individual switching states, binding affinity, and binding modulation upon switching. With a novel titration method the thermodynamic binding parameters were determined using reduced sample amounts. Employing these strongly enhanced molecular tweezers allowed to demonstrate photocontrol of intermolecular charge transfer in a reversible manner. Hemithioindigo based molecular tweezers with a comprehensively improved property profile are obtained by simple oxidation of the sulfur atom.![]()
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31
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Abstract
Cell‐cycle interference by small molecules has widely been used to study fundamental biological mechanisms and to treat a great variety of diseases, most notably cancer. However, at present only limited possibilities exist for spatio‐temporal control of the cell cycle. Here we report on a photocaging strategy to reversibly arrest the cell cycle at metaphase or induce apoptosis using blue‐light irradiation. The versatile proteasome inhibitor MG132 is photocaged directly at the reactive aldehyde function effectively masking its biological activity. Upon irradiation reversible cell‐cycle arrest in the metaphase is demonstrated to take place in vivo. Similarly, apoptosis can efficiently be induced by irradiation of human cancer cells. With the developed photopharmacological approach spatio‐temporal control of the cell cycle is thus enabled with very high modulation, as caged MG132 shows no effect on proliferation in the dark. In addition, full compatibility of photo‐controlled uncaging with dynamic microscopy techniques in vivo is demonstrated. This visible‐light responsive tool should be of great value for biological as well as medicinal approaches in need of high‐precision targeting of the proteasome and thereby the cell cycle and apoptosis.
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Supramolecular Relay-Control of Organocatalysis with a Hemithioindigo-Based Molecular Motor. J Am Chem Soc 2020; 142:19300-19307. [DOI: 10.1021/jacs.0c09519] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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Tuning the Ground and Excited State Dynamics of Hemithioindigo Molecular Motors by Changing Substituents. Chemistry 2020; 26:13507-13512. [PMID: 32692896 PMCID: PMC7702134 DOI: 10.1002/chem.202003096] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2020] [Indexed: 12/11/2022]
Abstract
Efficiency and performance of light triggered molecular motors are crucial features that need to be mechanistically understood to improve the performance and enable conscious property tailoring for specific applications. In this work, three different hemithioindigo-based molecular motors are investigated and all four steps in their complete unidirectional rotation are unraveled fully quantitatively. Transient absorption spectroscopy across twelve orders of magnitude in time is used to probe the fs nuclear motions up to the ms thermal kinetics, covering the timeframe of the whole motor rotation. The newly known full mechanisms allow simulation of the motor systems to scrutinize their performance at realistic illumination conditions. This highlights the importance of photoisomerization quantum yields for the rotation speed. The substitution pattern in close proximity to the rotation axle influences the excited and ground state properties. Reduction of electron donation and concomitant increase of steric hindrance leads to faster photoisomerization reactions with quasi-ballistic behavior, but also to a slight decrease in the quantum efficiency. The expected decelerating effects of increased sterics are primarily manifested in the ground state. A promising approach for next-generation hemithioindigo motors is to elevate electron donation at the rotor fragment followed by an increase of steric hindrance.
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Oxidized Hemithioindigo Photoswitches-Influence of Oxidation State on (Photo)physical and Photochemical Properties. Chemistry 2020; 26:10712-10718. [PMID: 32485011 PMCID: PMC7496871 DOI: 10.1002/chem.202002176] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2020] [Revised: 05/28/2020] [Indexed: 11/05/2022]
Abstract
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.
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Abstract
Indigoid chromophores have emerged as versatile molecular photoswitches, offering efficient reversible photoisomerization upon exposure to visible light. Here we report synthesis of a new class of permanently charged hemiindigos (HIs) and characterization of photochemical properties in gas phase and solution. Gas-phase studies, which involve exposing mobility-selected ions in a tandem ion mobility mass spectrometer to tunable wavelength laser radiation, demonstrate that the isolated HI ions are photochromic and can be reversibly photoswitched between Z and E isomers. The Z and E isomers have distinct photoisomerization response spectra with maxima separated by 40-80 nm, consistent with theoretical predictions for their absorption spectra. Solvation of the HI molecules in acetonitrile displaces the absorption bands to lower energy. Together, gas-phase action spectroscopy and solution NMR and UV/Vis absorption spectroscopy represent a powerful approach for studying the intrinsic photochemical properties of HI molecular switches.
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Active and Unidirectional Acceleration of Biaryl Rotation by a Molecular Motor. Angew Chem Int Ed Engl 2020; 59:5730-5737. [PMID: 31943681 PMCID: PMC7154650 DOI: 10.1002/anie.201913798] [Citation(s) in RCA: 46] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2019] [Revised: 12/09/2019] [Indexed: 12/11/2022]
Abstract
Light-driven molecular motors possess immense potential as central driving units for future nanotechnology. Integration into larger molecular setups and transduction of their mechanical motions represents the current frontier of research. Herein we report on an integrated molecular machine setup allowing the transmission of potential energy from a motor unit onto a remote receiving entity. The setup consists of a motor unit connected covalently to a distant and sterically encumbered biaryl receiver. By action of the motor unit, single-bond rotation of the receiver is strongly accelerated and forced to proceed unidirectionally. The transmitted potential energy is directly measured as the extent to which energy degeneration is lifted in the thermal atropisomerization of this biaryl. Energy degeneracy is reduced by more than 1.5 kcal mol-1 , and rate accelerations of several orders of magnitude in terms of the rate constants are achieved.
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Active and Unidirectional Acceleration of Biaryl Rotation by a Molecular Motor. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.201913798] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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39
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Proton-conduction photomodulation in spiropyran-functionalized MOFs with large on–off ratio. Chem Sci 2020. [DOI: 10.1039/c9sc04926f] [Citation(s) in RCA: 52] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
A spiropyran functionalized metal–organic framework is presented, allowing to photomodulate the aqueous proton conductivity by two orders of magnitude.
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Green light powered molecular state motor enabling eight-shaped unidirectional rotation. Nat Commun 2019; 10:4449. [PMID: 31575868 PMCID: PMC6773862 DOI: 10.1038/s41467-019-12463-4] [Citation(s) in RCA: 45] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2019] [Accepted: 09/10/2019] [Indexed: 11/09/2022] Open
Abstract
Molecular motors convert external energy into directional motions at the nano-scales. To date unidirectional circular rotations and linear motions have been realized but more complex directional trajectories remain unexplored on the molecular level. In this work we present a molecular motor powered by green light allowing to produce an eight-shaped geometry change during its unidirectional rotation around the central molecular axis. Motor motion proceeds in four different steps, which alternate between light powered double bond isomerizations and thermal hula-twist isomerizations. The result is a fixed sequence of populating four different isomers in a fully unidirectional trajectory possessing one crossing point. This motor system opens up unexplored avenues for the construction and mechanisms of molecular machines and will therefore not only significantly expand the toolbox of responsive molecular devices but also enable very different applications in the field of miniaturized technology than currently possible. Molecular motors have predominantly been limited to circular or linear directional motions. Here, the authors design a molecular motor that moves unidirectionally along a more complex figure-eight trajectory by a distinct four-step mechanism that alternates between photochemical and thermal reaction steps.
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Photoresponsive Molecular Switches and Machines. CHEMPHOTOCHEM 2019. [DOI: 10.1002/cptc.201900147] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Symmetric and nonsymmetric bis-hemithioindigos – precise visible light controlled shape-shifters. Org Chem Front 2019. [DOI: 10.1039/c9qo00202b] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
A series of bis-hemithioindigo photoswitches with different molecular setups are presented allowing precise manipulation of molecular shapes with visible light.
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Abstract
We report on the synthesis of a hemithioindigo molecular motor bearing thioether feet for metal surface attachment and a comprehensive study of its light induced unidirectional motion in solution.
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Photon-Only Molecular Motor with Reverse Temperature-Dependent Efficiency. J Am Chem Soc 2018; 140:16442-16445. [DOI: 10.1021/jacs.8b10660] [Citation(s) in RCA: 48] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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46
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Circular Dichroism Photoswitching with a Twist: Axially Chiral Hemiindigo. J Am Chem Soc 2018; 140:13558-13561. [DOI: 10.1021/jacs.8b07839] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
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47
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Übertragung unidirektionaler molekularer Motorrotation auf eine räumlich getrennte Biarylachse. Angew Chem Int Ed Engl 2018. [DOI: 10.1002/ange.201804716] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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48
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Transmission of Unidirectional Molecular Motor Rotation to a Remote Biaryl Axis. Angew Chem Int Ed Engl 2018; 57:11064-11068. [DOI: 10.1002/anie.201804716] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2018] [Revised: 06/04/2018] [Indexed: 12/23/2022]
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Cover Feature: 2-(4′-Pyridyl- N
-oxide)-Substituted Hemithioindigos as Photoresponsive Guests for a Super Aryl-Extended Calix[4]pyrrole Receptor (Chem. Asian J. 12/2018). Chem Asian J 2018. [DOI: 10.1002/asia.201800711] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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50
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2-(4'-Pyridyl-N-oxide)-Substituted Hemithioindigos as Photoresponsive Guests for a Super Aryl-Extended Calix[4]pyrrole Receptor. Chem Asian J 2018; 13:1632-1639. [PMID: 29660260 DOI: 10.1002/asia.201800463] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2018] [Indexed: 02/01/2023]
Abstract
We report the synthesis of two 2-(4'-pyridyl-N-oxide)-substituted hemithioindigos (HTIs). We probed their photoisomerization by using UV/Vis and 1 H NMR spectroscopy techniques. Light irradiation at λ=450 nm provoked the isomerization of the HTI Z isomer to the E counterpart to a large extent (≈80 % at the photostationary state). 1 H NMR titration experiments revealed the formation of thermodynamically and kinetically stable 1:1 inclusion complexes of the (Z)-HTI isomers with a super aryl-extended host (association constant>104 m-1 ). Photoirradiation at λ=450 nm of the inclusion complexes induced the isomerization of the bound HTI N-oxide to afford the (E)-HTI⊂calix[4]pyrrole complex. We determined accurate association constant values for the 1:1 inclusion complexes of the (Z)- and (E)-HTI isomers by using isothermal titration calorimetry experiments. The results showed that the stability constants of the (E)-HTI complexes were 2.2-2.8-fold lower than those of the (Z)-HTI counterparts, which explains the lack of light-induced release of the former to the bulk solution.
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