Photochromic Performance of Donor‐Acceptor Stenhouse Adducts in Polymer Binders and Solution

Abstract

Donor‐acceptor Stenhouse adducts (DASAs) are an exciting new class of negative photochromic compounds, offering high colouration and rapid photo‐switching speeds, however the relationship between binder properties and photo‐switching behaviour of DASAs in films is poorly understood. The determination and analysis of rate constants of seven DASAs in five polymer binders showed a complex relationship between the glass transition temperature (Tg) of the binder, the solubility parameters of the matrix and the push‐pull nature of the donor and acceptor moieties. The rate constants of photo‐switching steps that require large degrees of molecular motion such as the actinic and thermal carbon‐carbon double bond rotations (kbleach and k−1) were found to be highly dependent on the Tg of the polymer binder, with higher Tg binders restricting these processes, resulting in slower switching rates and impacting changes in colour intensity. Correlation of rate constants with the Hansen solubility parameter for solvents and binders revealed strong relationships between the sum of the polarity and hydrogen bonding parameters (δP+δH) and the actinic and thermal carbon‐carbon double bond rotations (kbleach and k−1). This is attributed to changes in the zwitterionic resonance contributions of the triene with increases in these two solubility parameters.

Visible light-responsive materials: the (photo)chemistry and applications of donor–acceptor Stenhouse adducts in polymer science

“…Section 2.5.4). Overall, the investigated DASA concentrations in the solid polymer matrices were rather low in the range of 0.5–8 wt%, 32,44,93,135 but sometimes higher, up to 17 wt%. 136…”

“…), as well as the type and concentration of DASAs in the polymer. In most cases, mixing has been achieved by co-dissolving the polymer and the DASA and fabricating polymer films or thin coatings by different methods, such as drop-casting, 32,94,135 spin coating 44,136 doctor blading, 93 or dip coating, 118 followed by a drying process to remove the solvent from the films. To date, glass substrates have been mainly employed to support the formation of DASA polymer films.…”

“…5a). 35,39,41,93 Representative absorbance profiles of A , B / B ′ and C are illustrated in Fig. 4c.…”

“…For actinic steps, rate constants are often measured as a function of light intensity to differentiate between thermal and photochemical contributions to the observed isomerization rate. 35,39,40,93,97,98 Usually, the thermal and photochemical rates are assumed to be independent, but this is only true if negligible photothermal heating occurs during illumination. Importantly, the rates of the photon-driven steps depend on the spectrum and intensity of the light source that is used.…”

Donor–acceptor Stenhouse adduct functionalised polymer microspheres

“…In the solid state, effective and reversible switching of polymer-bound DASAs is dependent on the polymer's glass transition temperature ( T g ). 41,47 When held at or above the host polymer's T g , DASA switching kinetics markedly improve. 38,41,46 Studies by Sroda et al .…”