Poly with spiropyran groups

Light-induced transformations from one structure to another have been studied with many modified polypeptides [13, 14] bearing pendant photochromic groups such as azobenzene or spiropyran groups. Typical examples are the modified poly(L-glutamic acids) PGA-1 and PGA-2 presented in Chart 5.5. 

These processes are called photochromic if considerable color changes occur during the photoisomerization. Poly(methacrylates) with certain spiropyran groups become colored on irradiation with light and subsequently decolorize slowly in the dark ... 

Many examples are known such as the Fries rearrangement in aromatic polyesters or in some poly(methyl methacrylates) with poly(spiropyran) groups. 

Poly(methacrylic acid) with spirobenzopyran pendant groups is soluble in polar solvents, such as methanol or water, when the content of spirobenzopyran is less than 20 mol%. A methanol solution of the polymer has a weak red color under thermal equilibrium conditions, which indicates the presence of merocyanine form in equilibrium with spiropyran form. Visible irradiation completely bleached the absorption (merocyanine - spiropyran) after the light was removed, the absorption gradually reappeared in the dark (spiropyran merocyanine). Ultraviolet irradiation caused enhancement of the absorption near 530 nm (merocyanine merocyanine) the intense absorption again returned to the thermal equilibrium intensity after removal of the light (merocyanine - spiropyran). Together with these isomerizations. 

Fig. 11 Proposed mechanism of mechanical activation of polyurethane containing UPy stacking end groups and spiropyran mechanophores. SP spiropyran, MC merocyanine, PTHF poly(tetra-hydrofuran). Reprinted with permission from [62], Copyright 2014 American Chemical Society...

Photoinduced mechanical response of a monolayer consisting of poly(methyl methacrylate) with spirobenzopyran pendant groups was examined at an air-water interface [55]. Irradiation with UV light pulses isomerized the spiropyran chromophore and led to a relative surface pressure increase of up to 10%. The pressure decreased progressively in the dark, and a typical decay time was estimated as being approximately 20 min. The decay can be accelerated by use of visible light pulses (Fig. 26). The whole process can be repeated several times. 

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