Isomerization behavior of aromatic azo chromophores bound to semicrystalline polymer films

Abstract

ABSTRACT:The cis-trans isomerization of azo chromophores covalently bound to semicrystalline polymer films was investigated. Various azo chromophores were introduced onto the functionalized semicrystalline polymer films by a chemical transformation reaction and their isomerization behavior was investigated by UV-visible spectroscopy and a contact-angle goniometer. The thermal Z 3 E isomerization rate of the azo moiety covalently bound to low-density polyethylene (LDPE) and polypropylene (PP) films was determined. The rate of thermal isomerization was also compared between amorphous and semicrystalline polymer films bearing azo chromophores. The effect of the intramolecular steric factor and the nature of chromophores was studied on the thermal isomerization rate of the polymer films.

Thermal Cis → Trans Isomerization of Covalently Attached Azobenzene Groups in Undrawn and Drawn Polyethylene Films. Characterization and Comparisons of Occupied Sites

“…940 min at 30°C in our Azo-PE or Azo/PE films (i.e., an ester linkage in conjugation with the azobenzene group) and 510 min at 25°C in the polyethylenes with amide linkages to azobenzene groups (i.e., an amide linkage in conjugation with the azobenzene group). 3 In drawn Azo-PE films, the thermal cis f trans isomerization at 65°C and below consists of a faster component (k 1 ) in addition to a slower component (k 2 ) that is comparable to the rate in the undrawn films at all temperatures (Table 1). Two parallel first-order cis f trans rate processes have been observed for azobenzene groups incorporated within the main chains of an annealed polymer as well, and the rate of the slower one is similar to the unique rate measured in newly prepared (unannealed) films.…”

“…3 There, the kinetics of thermal cis f trans isomerization were not cleanly first order. We suspect that the deviations from first-order derive from differences between sites at or near the film surfaces and in the interior rather than the nature of the amide linking group.…”

Azobenzene Polymers for Photonic Applications

“…A monolayer of azo-modified calixarene, when irradiated with a light gradient, produced a gradient in surface energy sufficient to move a macroscopic oil droplet , suggesting possible applications in microfluidics. Modest photoinduced contact angle changes for thin polymer films have also been reported (Sarkar et al, 2001). Recently an azobenzene copolymer assembled into polyelectrolyte multilayer showed a modest 21 change in contact angle with UV light irradiation.…”

“…Higher matrix crystallinity increases the rate of decay (Sarkar et al, 2001). The decay rate can act as a probe of local environment and molecular conformation (Tanaka et al, 2004;Norman and Barrett, 2002).…”

Photochemical and Photophysical Studies of and in Bulk Polymers

“…109 As one might expect, the effi ciency of trans → cis isomerization of azo moieties is reduced substantially in the glassy state of polymer hosts. 110,111 In the rubbery state, the thermal cis → trans isomerization of azo -containing polymers follows fi rst -order kinetics. 109 However, a portion of the isomerization is very fast in the glassy state, suggesting that polymer cavities force the guest molecules to adopt conformations that are closer to the transition state than those in isotropic solvents.…”