Control of Photodynamic Motions of Azobenzene‐Derivative Polymers by Laser Excitation Wavelength

Abstract

The dynamic properties of photoinduced alignment and surface relief grating (SRG) formation as a function of excitation wavelength (λex = 454, 488, 514, 532, 568, and 647 nm) are examined using five azobenzene‐derivative polymers, whose absorption spectra are tuned by substituting different electron‐withdrawing groups (CF3, CN, CNCl, NO2, (CN)2). The dynamics sensitively depend on λex. The fastest rate of photoinduced alignment is observed when λex is between λmax of the trans π–π* transition and that of the cis n–π* transition. A model of trans–cis photoisomerization has been developed based on competition between photoexcitation and relaxation, in which the n–π* transition has a faster relaxation pathway than the π–π* transition. Under conditions of adequate absorbance of the trans form at λex, i.e., greater than ${1 \over 2}$Amax, the rate of SRG formation increases at longer λex.

Structural and photoresponsive behavior of a series of (phenylene)azobenzene-containing liquid-crystalline methacrylic copolymers

“…To reduce the optical absorption of films in the presence of pre‐ordered molecular domains, some authors have proposed the use of azo‐LCPs with a low content of chromophore units. For instance, Hagen and Bieringer and Kim et al . reported photo‐addressable polymers in which azobenzene units and mesogenic side groups are incorporated into the same chain.…”

Photoinduced orientation and cooperative motion of three epoxy-based azo polymers

“…The influence can be rationalized by considering the isomerization efficiency of the azo chromophores and intermolecular interaction through hydrogen bonding. The trans-cis photoisomerization efficiency is dependent on the competition between excitation (p-p* or n-p* transition) and relaxation [51]. The trans-cis isomerization yield of the n-p* excitation is higher than that of the p-p* excitation.…”

Photoinduced birefringence of novel azobenzene poly(esterimide)s; the effect of chromophore substituent and excitation conditions

“…However, as it was shown recently, that knowledge of the optical response dependence on the writing wavelength is very precious since it allows for a proper selection of the excitation conditions that ensures the highest rate of the birefringence growth or the highest birefringence level [20,21].…”