Photoswitching of diarylethene polymers synthesized by TEMPO mediated polymerization

Optical and refractive index switching properties of diarylethene containing copolymers were studied. Polymers having different block distribution were synthesized from a controlled polymerization via living free radical method using ethyl α-2,2,6,6-tetramethylpiperidinyl-1-oxy-phenylacetate (ETEMPO) as an initiator. The diarylethene containing copolymers exhibited high thermal stability without loss of diarylethene unit up to 350°C. Photochromic films, having photochromic interconversion between colorless and red colored forms by UV and Vis laser sources, were prepared from the copolymers by solution coating method. The photochromic response of the copolymer was dependent on the distribution of diarylethene in the polymer and weight-average molecular weight (M _ω) of the polymers. Thus films of copolymers having random distribution of diarylethene showed larger photochromic absorbance change (ΔA) and photo induced refractive index change (Δn) as compared to that of block copolymer. The photochromic response was larger in a film of a random copolymer with lower Mw. Large all optically controllable refractive index switching (Δn ∼ 0.01) was achieved from the diarylethene copolymers, accompanied by photochromic interconversion between colorless and red colored forms.