Paululat, Thomas
Preferred name
Paululat, Thomas
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Publication Access status: Metadata only , Bis‐ and Tris‐norbornadienes with High Energy Densities for Efficient Molecular Solar Thermal Energy StorageMolecular solar thermal energy storage (MOST) systems can convert, store and release solar energy in chemical bonds, i.e., as chemical energy. In this work, phenyl‐ and naphthyl‐linked bis‐ and tris‐norbornadienes are presented as promising MOST systems with very high energy densities. The substrates were synthesized by Suzuki–Miyaura coupling reactions and their absorption properties and characteristic parameters for MOST applications were investigated. The norbornadiene derivatives showed absorption onsets of up to 386 nm and photoisomerization quantum yields of 56 % per photoisomerization event. The resulting quadricyclane products have half‐lifes up to 14 d and very high energy densities of up to 734 kJ/kg. Overall, these norbornadienes fulfill necessary criteria for an optimal MOST system and are, therefore, a highly promising basis for the development of materials for efficient solar energy conversion and storage.Source Type:Article3 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Extension of the π-system of monoaryl-substituted norbornadienes with acetylene bridges: influence on the photochemical conversion and storage of light energyThe photochromic norbornadiene/quadricyclane pair is a promising system for molecular solar thermal (MOST) energy storage, with which solar energy may be converted, stored, and released as heat in one integral molecular system. Herein, we present the synthesis of mono-, bis-, and tris-norbornadiene derivatives with alkynylbenzene and alkynylnaphthalene core units, along with studies of their photochemical properties. The target compounds were synthesized by Sonogashira–Hagihara coupling reactions of 2-bromonorbornadiene and the corresponding arylacetylenes. The norbornadienes showed absorption maxima in the range of 310–345 nm and long-wavelength zero onsets of up to 420 nm. The photoisomerization quantum yields were as high as 59% per photoisomerization event and the resulting quadricyclanes showed half-lives of up to 8 h at room temperature. Furthermore, the norbornadienes were transformed quantitatively into their quadricyclane photoproducts by irradiation with green light (520 nm) in the presence of a photosensitizer.Source Type:Article1 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Gilding the Lily: Studies on the Effects of Successive Loading of Light Energy‐Storing Molecules with Norbornadiene UnitsThe photochromic norbornadiene‐quadricyclane cycle has emerged as a promising basis for molecular solar thermal (MOST) energy storage. In this context, it has been established that multifunctional photoswitches with several norbornadiene units at one central aromatic core have favorable photochemical properties and storage capacities. Nevertheless, a maximum number of three norbornadiene units has been combined in one molecule, so far. In this work, scope and limits of this approach should be further assessed. Thus, exemplary polyfunctionalized derivatives have been synthesized by Suzuki‐Miyaura reactions, and their suitability for MOST applications was investigated. These compounds were converted into the corresponding quadricyclanes by direct UV irradiation ( λ ex =315 nm) with moderate quantum yields, whereas the reaction is more efficient upon irradiation with λ ex =520 nm in the presence of photosensitizers. But these molecules showed low stabilities and short half‐lives of 1 to 2 days. Moreover, the photochemical reaction is hampered by the close vicinity of photoactive units. Therefore, it appears that in such assemblies, a maximum number of three norbornadiene units is the limit to keep the optimal balance of photochemical properties required for MOST applications.Source Type:Article3 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Reversible Restrain and Release of the Dynamic Valence Isomerization in a Shape‐shifting Bullvalene by Complex FormationIn search for structural features that enable the control of the valence isomerization of the fluxional bullvalene, a bullvalene‐bis(harmane) conjugate is identified that acts as chelating ligand in complexes with metal ions. Spectrometric titrations show that this ligand forms 1 : 1 complexes with Ag + , Cu + , Cu 2+ , and Zn 2+ . Most importantly, detailed NMR‐spectroscopic analysis at different temperatures reveals that the complexation with Ag + strongly affects the dynamic isomerization of the bullvalene unit of the ligand such that only one predominant valence isomer is formed, even at 5 °C. Detailed 1 H‐NMR‐spectroscopic studies disclose an increased barrier (~11 kJ mol −1 ) of the Cope rearrangement. Furthermore, the addition of hexacyclene displaces the Ag + from the complex, so that the valence isomerization is accelerated and an equilibrium with two predominant isomers is formed. In turn, repeated addition of Ag + regains the complex with the restrained isomerization of the bullvalene unit. This method to control the valence isomerism by straightforward chemical stimuli may be used to simplify structural analysis at elevated temperatures, i. e. a feature not available so far with bullvalenes, and it may be employed as functional element in dynamic supramolecular assemblies.Source Type:Article1 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Stepwise Dissipative Control of Multimodal Motion in a Silver(I) CatenateStepwise dissipative control of two distinct motions, i.e., shuttling and sliding, is demonstrated in a single multicomponent device. When [2]rotaxane 1 , which acts as a biped, and deck 2 were treated with AgBF 4 /PhCH 2 Br+NEt 3 as chemical fuel, the transient catenate [Ag( 1 )] + ⋅ [Ag 3 ( 2 )] 3+ was instantly generated showing multimodal motion and autonomous return to 1 and 2 . In the dissipative process, catenate [Ag( 1 )] + ⋅ [Ag 3 ( 2 )] 3+ cleanly transformed into the follow‐up transient device ( 1 ) ⋅ [Ag 3 ( 2 )] 3+ exhibiting only sliding motion. Two interference‐free dissipative cycles proved the resilience and robustness of the process.Source Type:Article
