Synthesis, Structure, and Properties of Supramolecular Photoswitches Based on Ammonioalkyl Derivatives of Crown Ether Styryl Dyes

The synthesis of
new styryl dyes derived from 4-pyridine and 4-quinoline
and having an ammonioalkyl N-substituent and benzocrown
ether moieties of different sizes and with different sets of heteroatoms
was developed. Spontaneous “head-to-tail” dimerization
of these dyes via the formation of numerous hydrogen bonds between
the terminal NH3+ groups and crown ether moieties
was detected in MeCN solutions. The stability constants of the dimeric
complexes having pseudocyclic structure were studied by 1H NMR titration. The most stable complexes (log Kd up to 8.2) were found in the case of dyes with the 18-crown-6
ether moiety, which is most complementary for binding a primary ammonium
group. Stacking interaction of the conjugated systems in the dimeric
complexes contributes to their stability to a much lesser extent.
In dimeric complexes, the ethylene bonds of the dyes are preorganized
for stereospecific [2 + 2] photocycloaddition (PCA) induced by visible
light. PCA yields only rctt isomers of bis-crown-containing
cyclobutane derivatives. The dyes were studied by X-ray diffraction;
it was found that the dimeric arrangement is also retained in the
crystalline state. The possibility of topochemical PCA of the dyes
in single crystals without their destruction was demonstrated. The
possibility of retro-PCA of the obtained cyclobutane derivatives to
give the starting dyes was shown. The elucidated regularities of PCA
can be used to fabricate optical data recording systems based on ammonioalkyl
derivatives of crown ether styryl dyes.