Suppression of Undesirable Isomerization and Intermolecular Reactions of Double Bonds by a Linked Rotaxane Structure

Abstract

For luminescent materials, the isomerization and intermolecular reactions of their double bonds are often undesirable because they cause a reduction in the luminescence properties of the π-system. Herein, we report a new methodology to simultaneously prevent isomerization and intermolecular reactions by utilizing the steric effect of a linked rotaxane structure. The ring units are covalently linked in order to prevent any undesired shuttling effect from occurring during isomerization. In addition, the insulated structure provides robust optical properties by prevention of intermolecular reactions. Bulky linked rotaxane structures on both sides of the N=N and C=C double bonds suppress E/Z isomerization; photoluminescence quantum yield (PLQY) measurements reveal that this results in suppression of PLQY reduction caused by isomerization. Moreover, an improvement in the stability under light irradiation and air atmosphere is demonstrated.

Palladium-Catalyzed Sequential Three-Component Cross-Coupling to 1,3-Dienes: Employing Alkenes as Hydride and Alkenyl Donors

“…Furthermore, the carbazole moiety could be well introduced to the compound 4j , affording 10a in 95% yield . With appropriate conditions, the Sonogashira coupling reaction of 4j and ethynyltrimethylsilane proceeded smoothly to provide the alkynylated product 11a , which could be further transformed to the terminal alkyne 12a in 96% yield under the treatment of K 2 CO 3 …”

“…18 With appropriate conditions, the Sonogashira coupling reaction of 4j and ethynyltrimethylsilane proceeded smoothly to provide the alkynylated product 11a, which could be further transformed to the terminal alkyne 12a in 96% yield under the treatment of K 2 CO 3 . 19 Notably, products 4j, 4m, 4ai, 4an, 4ao, and 8a−8c were selected as representative compounds and their photophysical properties were investigated in highly dilute solution and powder. The photophysical data are summarized in Table S1, and the corresponding emission and UV absorption spectra are given in Figures S2−S9.…”

“…Analytical thin-layer chromatography was performed by using commercially prepared 100−400 mesh silica gel plates (GF 254 ), and visualization was effected at 254 nm. 1 H, 13 C, and 19 F NMR spectra were recorded using a Bruker DRX-400 spectrometer using chloroform-d (CDCl 3 ) containing 0.03% (v/v) tetramethylsilane (TMS) as a solvent. The chemical shifts are referenced to signals at 0.00 and 77.0 ppm, respectively.…”

Linked Rotaxane Structure Restricts Local Molecular Motions in Solution to Enhance Fluorescence Properties of Tetraphenylethylene

“…The insulation structure of ins-TPE is expected to prevent undesirable reactions leading to fading and discoloration. [46] Consequently, the UV-Vis and PL spectra of ins-TPE were not affected by the intense light irradiation at 365 nm, while the spectra of unins-TPE were drastically changed under the same condition (Figure 5A, B). Upon the light irradiation on unins-TPE, a new emission band appeared at approximately 400 nm, changing the fluorescence color (Figure 5C).…”

“…[39][40][41][42][43] The linked rotaxane structure can tightly fix a bulky macrocycle on a specific part of the axle because the covalent linkage inhibits the shuttling motions of the macrocycle. [41,[44][45][46] We envision that the bulky macrocycle around the fluorescent dye could enhance the rigidity of the fluorophore by inhibiting its local molecular motions. To date, methods with encapsulation structures, such as host-guest complexes [27][28][29][30][31][32][33] and rotaxane structures, [47][48][49][50][51] have been used to prevent the molecular motions of fluorophores.…”