Precious metal-free molecular machines for solar thermal energy storage

Abstract

Four benzothiazolium crown ether-containing styryl dyes were prepared through an optimized synthetic procedure. Two of the dyes (4b and 4d) having substituents in the 5-position of the benzothiazole ring are newly synthesized compounds. They demonstrated a higher degree of trans–cis photoisomerization and a longer life time of the higher energy forms in comparison with the known analogs. The chemical structures of all dyes in the series were characterized by NMR, UV–vis, IR spectroscopy and elemental analysis. The steady-state photophysical properties of the dyes were elucidated. The stability constants of metal complexes were determined and are in good agreement with the literature data for reference dyes. The temporal evolution of trans-to-cis isomerization was observed in a real-time regime. The dyes demonstrated a low intrinsic fluorescence of their Ba2+ complexes and high yield of E/Z photoisomerization with lifetimes of the higher energy form longer than 500 seconds. Density functional theory (DFT) calculations at the B3LYP/6-31+G(d,p) level were performed in order to predict the enthalpies (H) of the cis and trans isomers and the storage energies (ΔH) for the systems studied.

Accumulation of the photonic energy of the deep-red part of the terrestrial sun irradiation by rare-earth metal-free E–Z photoisomerization

“…2a (the blue line) refers to the formation of the trans-dye-Ba 2+ complex. 5 As is shown in Fig. 2b, the formation of cis-dye-Ba 2+ isomers caused a monotonic decrease of the visible sample absorption.…”

“…In a recently published work, 5 one of the possible strategies for the synthesis of target dyes 4a-4d (Scheme 1) was described. In the published procedure, 5 the first reaction step was quaternization of benzothiazoles with the corresponding alkane sultones, and the reaction was carried out in the absence of a solvent.…”

“…In a recently published work, 5 one of the possible strategies for the synthesis of target dyes 4a-4d (Scheme 1) was described. In the published procedure, 5 the first reaction step was quaternization of benzothiazoles with the corresponding alkane sultones, and the reaction was carried out in the absence of a solvent. Such reaction conditions have their advantages, but a major drawback is the accumulation of an insoluble product in the reaction volume, and after a certain point it is difficult to complete the quaternization.…”

“…In the same work 5 on the synthesis of 4-(aza-15-crown-5) benzocarbaldehyde (3), the use of a modified four step synthetic procedure was described. 6 Led by the will to create an economical, reproducible and simple synthetic scheme through the combination of a few known methods, [5][6][7][8] in this work a new, more robust, easy-to-implement, cost-effective and only two-step procedure was created for the preparation of intermediate 3 (Scheme 1B).…”

“…In the same work 5 on the synthesis of 4-(aza-15-crown-5) benzocarbaldehyde (3), the use of a modified four step synthetic procedure was described. 6 Led by the will to create an economical, reproducible and simple synthetic scheme through the combination of a few known methods, [5][6][7][8] in this work a new, more robust, easy-to-implement, cost-effective and only two-step procedure was created for the preparation of intermediate 3 (Scheme 1B). The crucial optimisation step in this procedure is the neutralization of the reaction mixture after the Vilsmeier-Haack-Arnold reaction, with the milder reagent, sodium acetate instead of the aggressive sodium hydroxide 8 which is reported to cause ring opening and damage of the crown functionality (TLC monitoring, NMR).…”