Dynamic and photochemical behavior of amorphous comb-like copolymers with photochromic azobenzene side groups

Abstract

SUMMARY: A series of amorphous photochromic homo-and copolymethacrylates with an azobenzene moiety in the side group is investigated systematically by optical and dielectric spectroscopy. The aliphatic ester component of the comonomer unit and the concentration of the azobenzene groups within the copolymer are varied. The kinetics and the temperature dependence of the E/Z (trans/cis) photoisomerization and of the thermal Z/E (cis/trans) isomerization is studied for spin-coated films of the polymers. To understand the polarity of the polymeric materials as well as the matrix dependence of the reactions and of the photoinduced reorientation processes in the steady state molecular dynamics is investigated by dielectric spectroscopy. A variety of relaxation processes is observed: a -relaxation is detected for polymers containing azobenzene moieties. The temperature dependence of the reaction rate of the thermal Z/E isomerization process measured by optical spectroscopy seems to correlate with the values of the b 9 -process. A correspondence between dielectric and photochemical behavior is discussed.

Photoinduced Motions in Azo-Containing Polymers

“…These measurements are very valuable, since the frequency and the temperature could be varied. The method was applied to solid solutions of small azo dyes, 123 on amorphous azo copolymers, 124 in "frustrated" liquid crystalline co-polymers 125 [frustrated is used here for liquid crystalline materials with high Tg, where the photoinduced motions occur in the amorphous (glassy) state] and to pinpoint cooperative motions in liquid crystalline azo oligomers. 126 By far the most popular and informative spectral method to analyze the photoinduced motion is FTIR.…”

Synthesis and Characterization of Copolymers of Methyl Methacrylate and 11-(4-Ethoxyazobenzene-4′-oxy)undecyl Methacrylate

“…Such interaction is common for polymers with polar azobenzene side chains, [25,38] or in Langmuir-Blodgett films, [39] but generally does not occur in non-polar side chain polymers. [27,40] The broken lines in Figure 3 represent absorption spectra of the copolymer sample after irradiation with 366 nm light. The ultraviolet absorption band of cis-azobenzene has a maximum at shorter wavelengths than does transazobenzene, [1] and the maximum value of the extinction coefficient, e, is much lower.…”

“…The cis fraction at the photostationary state can be estimated as 0.7-0.8 using the ratio e cis /e trans = 0.01 at 360 nm, a value that has been determined for a very similar ethoxy-azobenzene. [40] The cis fraction after irradiation was the same for all studied copolymers, both as films and in solution. The cis yield is thus not significantly affected by the amount of azo-MA, which is in accordance with previously published data on azobenzene copolymers with long spacers.…”

“…This is at least ten times less than for "amino type" or "stilbene type" azobenzenes. [26] An exception is the very large rate constant (k = 5-10 min -1 ) that has been reported by Fritz et al [40] for a side chain azobenzene polymer of the azobenzene type. The thermal isomerization of this compound was also unique in that it followed firstorder kinetics in the solid state.…”

Controlling the reversible wetting capability of smart photochromic-polymer surfaces by micro patterning

“…The photochromic molecules undergo the reversible isomerization process even when incorporated within macromolecular matrices [16][17][18], interchanging between the non-polar SP and the polar MC form. This change induces an overall change in the polarity of their host polymers [19,20], thus modifying also their surface polarity. As a result, the surfaces exhibit enhanced hydrophilicity after UV irradiation and enhanced hydrophobicity after visible light irradiation [11,12].…”