A material whose enzymatic degradation is initiated by an external stimulus is of great importance from the viewpoint of practical biodegradable polymers. In this context, we developed a method that controls the initiation of enzymatic degradation by light. 4,4′-Didecyloxy-3-methylazobenzene (Azo), which melts upon exposure to UV radiation, was coated onto biodegradable poly(L-lactide) and the enzymatic degradation of the polymer by proteinase K was successfully initiated and controlled by tuning the solid–liquid transition of the azo-based compound. This stimulus-triggered enzymatic degradation is a significant contribution to the development of lifetime-controlled biodegradable materials.

The direct and reversible transformation of matter between the solid and liquid phases by light at constant temperature is of great interest because of its potential applications in various manufacturing settings. We report a simple molecular design strategy for the phase transitions: azobenzenes having para-dialkoxy groups with a methyl group at the meta-position. The photolithography processes were demonstrated using the azobenzene as a photoresist in a single process combining development and etching of a copper substrate.

Liquid-crystalline macrocyclic compounds, tethered by two or three azobenzenes bearing alkoxy side chains, exhibit isothermal phase transitions from liquid-crystal to isotropic as well as from crystal to isotropic phases upon light irradiation due to the drastic conformational change of their macrocyclic backbone.

The photochromic behavior of a spiroperimidine compound, 2,3-dihydro-2-spiro-7′-(8′-imino-7′,8′-dihydronaphthalen-1′-amine)perimidine (PNI), doped in various polymers has been studied. Upon irradiation with 405 nm light, PNI exhibits photochromism, and a color change (light yellow to brown) is observed. The initial (closed) and colored (open) forms exhibit absorption maxima (λmax) around 400 and 500 nm, respectively. The open form possesses a wide absorption band, extending to ∼750 nm. Little effect of the polymer matrix on the λmax of either the closed or open forms was observed, and these values were also similar to those in solution. The lifetime of the open form depends mainly on the glass transition temperature (Tg) of the polymer, and ranges from, for example, 11 min to 5.4 d. This indicates that the lifetime of the open form can be readily tuned by simply choosing a suitable polymer matrix. Photochromism in different polymer substrates are demonstrated herein.

The photochromic behavior of two spiroperimidine compounds, 2,3-dihydro-2-spiro-7′-(8’-imino-7′,8′-dihydronaphthalen-1’-amine)perimidine, PNI and 2,3-dihydro-2-spiro-4′-[8′-aminonaphthalen-1′(4H)-one]perimidine, PNO-p has been studied by absorption and transient absorption spectroscopies. Both PNI and PNO-p exhibit extremely large solvent effect on the thermal back reaction from the colored (open) to the initial (close) state. The lifetime of the colored state ranges from 600 μs (methanol) to 22 days (acetonitrile) at room temperature. The relative energies of isomers have been estimated by the DFT calculations.

Liquid-crystalline macrocyclic compounds, tethered by two or three azobenzenes bearing alkoxy side chains, exhibit isothermal phase transitions from liquid-crystal to isotropic as well as from crystal to isotropic phases upon light irradiation due to the drastic conformational change of their macrocyclic backbone.