Supramolecular Dimerization and [2 + 2] Photocycloaddition Reactions of Crown Ether Styryl Dyes Containing a Tethered Ammonium Group: Structure–Property Relationships

Abstract

Molecular self-assembly is an effective strategy for controlling the [2 + 2] photocycloaddition reaction of olefins. The geometrical properties of supramolecular assemblies are proven to have a critical effect on the efficiency and selectivity of this photoreaction both in the solid state and in solution, but the role of other factors remains poorly understood. Convenient supramolecular systems to study the structure-property relationships are pseudocyclic dimers spontaneously formed by styryl dyes containing a crown ether moiety and a remote ammonium group. New dyes of this type were synthesized to investigate the effects of structural and electronic factors on the quantitative characteristics of supramolecular dimerization and [2 + 2] photocycloaddition in solution. Variable structural parameters for the styryl dyes were the size and structure of macrocyclic moiety, the nature of heteroaromatic residue, and the length of the ammonioalkyl group attached to this residue. Quantum chemical calculations of the pseudocyclic dimers were performed in order to interpret the relationships between the structure of the ammonium dyes and the efficiency of the supramolecular photoreaction. One of the dimeric complexes was obtained in the crystalline state and studied by X-ray diffraction. The results obtained demonstrate that the photocycloaddition in the pseudocyclic dimers can be dramatically affected by the electronic structure of the styryl moieties, as dependent on the electron-donating ability of the substituents on the benzene ring, and by the conformational flexibility of the pseudocycle, which determines the mobility of the olefinic bonds. The significance of electronic factors is highlighted by the fact that the photocycloaddition quantum yield in geometrically similar dimeric structures varies from ≤10(-4) to 0.38. The latter value is unusually high for olefins in solution.

Cyanine Dyes Containing Quinoline Moieties: History, Synthesis, Optical Properties, and Applications

“…These salts are an essential step in the synthesis of cyanine dyes. A lot of different types of salts have been synthesized and various methods have been optimized [30–34] . There are over 180 published salts synthesized by various methods from quinaldine and almost 450 salts from lepidine [28] …”

“…Most of them are synthesized from lepidine and quinaldine directly, for example, salts 1 – 6 (Scheme 4) and 8 – 13 (Scheme 5), whereas some of them require a different initial reagent, such as diphenylamine for the synthesis of salts 7 (Scheme 4) and 14 (Scheme 5). [30, 31, 33–48] …”

Reversible photoswitching of the DNA-binding properties of styrylquinolizinium derivatives through photochromic [2 + 2] cycloaddition and cycloreversion

“…Therefore, suspensions of 3b und 3c in water were irradiated with an LED lamp at 450-470 nm to give the 2,2'-(2,4-diphenyl-1,3-cyclobutanediyl)bisquinolizinium 4b and 4c as photoproducts in quantitative yield. The products 4b and 4c were fully characterized by NMR spectroscopy ( 1 H, 13 C, COSY, HSQC, HMBC, and ROESY) and mass spectrometry, which revealed a cyclobutane structure, specifically by the appearance of the characteristic NMR signals of the cyclobutane at 4.89-5.00 ppm [42][43][44][45][46]. Unfortunately, detailed 2D NMR and spectroscopic analyses did not allow a conclusive assignment of the configuration of the products.…”

“…However, this system was not applied for photoinduced switching of binding properties [36]. Apparently, styryl-substituted aromatic derivatives could fill this gap because the [2 + 2] photocyclization reaction of stilbenes and derivatives thereof is a well-established reversible photoreaction [37][38][39][40][41][42][43][44][45][46], and styryl dyes, in particular cationic ones, were shown to be efficient DNA binders [47][48][49][50][51][52][53][54][55][56][57][58]. Nevertheless, the photochromic nature of DNA-binding styryl dyes has not been applied to use them as photoswitchable DNA binders.…”

Photoinduced hydrogen-bonded self-assembly of cation-capped complexes and novel photoswitchable supramolecular devices based on (aza)-18-crown-6-containing styryl dyes bearing a long N-ammonioalkyl substituent

“…Previously, it was found using 1 H NMR spectroscopy that dyes (E)-1a and (E)-1d in MeCN-d 3 form anti-head-to-tail pseudocyclic dimers as a result of spontaneous self-assembly via hydrogen bonding between the terminal ammonium group of one dye molecule and the crown ether moiety of the other molecule (Scheme 3). 22,34 Chart 1 Crown ether styryl dyes (E)-1 and (E)-2. The structure of dimeric complex [(E)-1a] 2 in the crystal was proved using X-ray diffraction analysis.…”