Solubility control of organic acid-base salts by photochromism

All‐Optical Fine‐Tuning of Absorption Band of Diarylethene with Photochromic Acid‐Generating Spiropyran

“…However, irradiation with 366‐nm light of the precipitate suspension led to the dissolution of the solid as the photocyclization proceeded. Thus, the solubility of the material and the near‐IR light permeability through the system could be controlled by the photochromic reaction between 1o and 1c …”

“…Although the spectroscopic properties of 1o and 1c were changed by complexation with the Cu(I) ion as a Lewis acid in acetonitrile to show a metal‐to‐ligand charge transfer (MLCT) band at around 450 nm and a 13 nm bathochromic shift of the main absorption band in the visible region, respectively, they were not induced by the addition of oxalic acid. However, when 4 eq of trifluoromethanesulfonic acid (TfOH) was added, the maximum absorption wavelength of 1c in chloroform shifted from 638 to 684 nm, i.e., a 46 nm bathochromic shift ( Figure ), and the Job's plot proved that one molecule of 1c accepted two protons . The apparent absorption spectrum of the system composed of 1c and TfOH was the result of the sum of the net absorption spectra of the protonated and nonprotonated species.…”

“…However, all previous literature have reported on the addition of a strong acid with subsequent neutralization by the addition of a base. This method is impractical for applications in photon‐working displays or optical shutters . A system which works without any additional species and can be switched by outside stimuli such as light irradiation is strongly desired.…”

Gated Photochromic System of Diarylethene with a Photon-Working Key

“…Recently, we reported the all-optical fine-tuning of the absorption band position for the closed form of a bisthienylethene, possessing two phenanthroline groups on both thiophene rings, by generating a strongly acidic spiro form of spiropyran 2 ( 2sp ) from the weakly acidic merocyanine form ( 2mc ) by irradiation with 450 nm light . This spiropyran, whose most stable state is the ring-opened merocyanine form, was designed by modification of Liao’s sulfo-group-bearing water-soluble spiropyran 3 . − This modification increased the acidity of the spiro form by introducing a fluorine atom on the phenyl group of the indoline moiety and afforded higher solubility in the organic solvents by introducing a 2-methyl-2-propyl group ( tert -butyl group) on the phenol ring.…”