Development of novel deep-red/near-infrared fluorescent dyes based on a pyridinium–cyclic enolate betaine skeleton

Water detection in organic solvents using a copolymer membrane immobilised with a fluorescent intramolecular charge transfer-type dye: effects of intramolecular hydrogen bonds

“…Furthermore, to clarify the effects of the PB structure on the water detection sensitivity, the intramolecular hydrogen bonds between the carbonyl oxygens of the cyclic enolate and the α-hydrogens of the pyridinium ring were targeted for analysis. As reported previously, 49,50 the α-hydrogens of the pyridinium ring exhibited a large chemical shift in proton NMR to 9.73 ppm (in CDCl 3 ), whereas that of QP1 was 9.10 ppm (in CDCl 3 ) (Fig. S14†), because the carbonyl oxygen and α-hydrogens tended to form intramolecular hydrogen bonds.…”

“…49 Moreover, the same group reported that π-extension and the introduction of a donor such as an N , N -diphenylamino group to PB structure resulted in exhibiting enhanced fluorescence; additionally, the dyes were found to exhibit solvatochromic behaviour owing to their donor–acceptor (D–A)-type structures. 50 By imparting ICT characteristics to the PB structure, the sensitivity to water and detection range would be changed. In anhydrous organic solvents, PB dyes form a planar structure owing to their intramolecular hydrogen bonds, whereas in the presence of water, the intramolecular hydrogen bonds are weakened by intermolecular hydrogen bonds between the dye and water (Fig.…”