Aggregates in Langmuir–Blodgett Films of Spiropyrans Having Hydroxyl or Hydroxymethyl Group

Abstract

The optical properties of monomolecular layers at an air–water interface and also of Langmuir–Blodgett (LB) films of several photochromic spiropyrans with a single hydrophobic long chain and either a hydroxyl or a hydroxymethyl group have been investigated. Changes in the optical spectra of these films were induced by either UV irradiation or heating. UV-visible, and IR absorption spectra showed that spiropyran SP145 formed J-aggregates and SP147 formed H-aggregates. The half-decay period of the J-aggregate to the spiropyran (SP) form was longer than that of the colored monomeric photomerocyanine (PMC) to the SP form. It was concluded that hydrogen bonding between neighboring colored PMC molecules via hydroxyl, hydroxymethyl, and nitro groups stabilizes the aggregate state.

Stimuli-responsive surfactants

“…59 Since then much work has been carried out on control of micellar morphology, 59 wettability 60 and the preparation of Langmuir Blodgett films. [61][62][63] In 2010, the first report of the self-assembly of spiropyran-modified surfactants (SP-Me-6, Figure 9) on colloidal and flat silica was published. 64 Importantly, this work was carried out in an aqueous medium and investigated in situ morphological changes in the adsorbed layer, induced by photoisomerization.…”

Photo-isomerization of spiropyran-modified cationic surfactants

“…This means that the photoisomerization from the SP form to the MC form (and vice versa) is structurally reversible. Since the photochromic behavior was firstly reported in 1952 [20], various kinds of water-insoluble SP-modified amphiphiles have been synthesized with a view to developing photo-responsive Langmuir-Blodgett (LB) films formed at the air/solution interface [21][22][23][24]. Indeed, the photoinduced isomerization causes a dramatic change in the hydrophilic/hydrophobic nature of the substance (apparently, the zwitterionic MC form is more hydrophilic than the nonionic SP form) [25].…”

Study on the Chemical Reaction of Spiropyran in Medium- and High-Density Fluids

“…15, 16 Among various kinds of spiropyrans, 6-nitro-BIPS has been intensively studied; [16][17][18][19][20][21][22] its reaction scheme is depicted in Figure 1. The zwitterionic merocyanine form, which is created upon ultraviolet excitation, thermally isomerizes to the nonionic spiro form.…”