Relationship between Activation Volume and Polymer Matrix Effects on Photochromic Performance: Bridging Molecular Parameter to Macroscale Effect

Abstract

Photochromic compounds have attracted attention as ophthalmic lenses because of their reversible color modulation upon irradiation with light. However, the efficiency of the photochromism is strongly affected by their surrounding because of the structural changes concomitant with the photochromism, which causes the decrease in the photochromic performance in the polymer matrix. Therefore, the clarification of the degree of the structural changes is necessary to apply to the ophthalmic lenses. Bridged imidazole dimers are one of the fast photoswitch molecules possessing high photochromic quantum yield and durability. Although the enhancement of the photochromic properties of bridged imidazole dimers has been vigorously studied, the quantitative information about the structural changes has not been revealed in detail. In this study, we investigated the pressure effects on the photochromic properties of bridged imidazole dimers. The activation volume for the thermal back-reaction of the photogenerated biradical species becomes an effective measure to predict the degree of the structural change during the photochromic reaction. We revealed that the smaller activation volume is suitable for keeping the efficient photochromic reaction in the polymer matrix because the photochromic reaction is not affected by the surroundings. These fundamental insights into the molecular dynamics provide valuable information to develop fast photochromic compounds that are suitable for the use in the polymer matrix and pressure sensitive photochromic materials.

Wavelength-Selective Light-Responsive DASA-Functionalized Polymersome Nanoreactors

“…Notably, both dispersions show a reduction in their absorbance when irradiated with white light but at a much slower rate than the THF solutions and without complete disappearance of the DASA peaks, even after longer additional irradiation for 3 min (gray curves). Such a difference is not unexpected, because the DASAs in the polymersome membrane are located in a polymer matrix in which the chains are less flexible than in solution. ,− To assess the matrix stiffness, we performed DSC measurements of the DASA block copolymers and found glass transition temperatures ( T g ) of 30 °C for MELD and 30 °C for PYRA (Figure S14). Both values are higher than the T g of a poly­(HMA) homopolymer (−5 °C), most probably due to the DASA-modified monomer units that raise the T g as reported previously. , …”

Nano‐3D‐Printed Photochromic Micro‐Objects

“…The physical properties of a polymer matrix, in particular its stiffness/softness and the amount of polymer free volume can impede or allow the required dynamic motion on the molecular level during photoswitching. [38,39] Therefore, we utilized in situ photorheology (Figure S7, Supporting Information) to assess the mechanical properties and photoreactivity of the resulting networks. Soft polymer matrices from low-T g polymers generally provide the best conditions for the photoswitching of photochromic compounds with large changes in molecular shape.…”

Efficient coloration and decoloration reactions of fast photochromic 3H–naphthopyrans in PMMA-b-PBA block copolymer

“…Generally, the investigation of pressure effect on the rate of chemical reactions provides the important insights into the conformational changes during chemical reactions [14][15][16]. We previously demonstrated that the value of the activation free volume (ΔV ‡ ) for the thermal back reaction is an effective measure to evaluate the efficiency of the photochromic reaction in polymer matrix [17,18]. The other solution is to reduce the viscosity of a host polymer matrix [10,[19][20][21].…”