Enabling Lower Energy Light Harvesting in Stilbene-Based Photomechanical Polymers via Triplet Sensitization

Abstract

Photoresponsive polymers, typically activated with direct excitation of an azobenzene moiety, are an intriguing class of materials for application as adaptive structures. Here, we introduce triplet excited state sensitization as a mechanism to harness light in a stilbene-based photopolymer (i.e., the carbon analogue of azobenzene). While the undoped film shows no response, the sensitized film exhibits polarization dependent bending under 445 nm irradiation via (1) sensitizer excitation, (2) triplet energy transfer, (3) stilbene isomerization, and (4) subunit reorientation. This work is the first to demonstrate stilbene-based photopolymers and triplet sensitization as a low energy light harvesting mechanism in photomechanics.

Triplet sensitization enables bidirectional isomerization of diazocine with 130 nm redshift in excitation wavelengths

“…[21][22][23][24][25][26][27][28] Unlike conventional azobenzene, whose triplet state properties have been investigated since the 1960s, 29 no studies on the triplet states of diazocine molecules have been published. Knowledge of the triplet state properties has been exploited to achieve sensitized photoswitching of conventional azobenzenes 30 (Scheme 1) in addition to other classes of molecules, such as diarylethenes, 31,32 overcrowded alkenes, 33 stilbenes, 34,35 indigos 36 and norbornadienes. 37 Compared to the direct excitation of the photoswitch, triplet sensitization enables photoswitching with red-shied excitation wavelengths from the ultraviolet and blue, even towards near-infrared.…”

Photochromic Uranyl-Based Coordination Polymer for Quantitative and On-Site Detection of UV Radiation Dose

“…Photochromic materials often exhibit both reversible color changes and physicochemical property variations in response to UV or visible light, which make them draw considerable attention with their potential ability for application in fields of optical memories, , displays, , photomechanics, smart windows, − photoswitches, , and so on. Generally speaking, the color of photochromic materials will undergo obvious variations with the accumulation of light irradiation dose.…”

“…Typical photochromic organic molecules (e.g., diarylethene, , spiropyran , and azobenzene , ) undergo isomerization upon light illumination, accompanied by reversible color changes. Moreover, viologen and its derivatives exhibit an electron-deficient nature and often combine electron donors to construct photochromic materials. − However, it is well known that purely photochromic organic molecules usually suffer from insufficient stability. , For instance, the photogenerated colored forms of these molecules are optically and thermally unstable, significantly restricting their applications in real world. − In the past two decades, numerous photochromic inorganic–organic hybrid materials, especially coordination polymers (CPs) or metal–organic frameworks (MOFs), have been developed, showing potential applications in visualized UV monitoring. ,,, However, this type of UV detection strategy can only offer semiquantitative dose information. In addition, the reported photochromic MOFs/CPs are not sensitive enough, as they often take tens of seconds or even longer to achieve color changes when exposed to UV radiation. − Therefore, it remains a challenge to develop high-sensitive and quantitative UV dosimeters based on photochromic materials.…”

“…42−44 In the past two decades, numerous photochromic inorganic− organic hybrid materials, especially coordination polymers (CPs) or metal−organic frameworks (MOFs), have been developed, showing potential applications in visualized UV monitoring. 11,24,45,46 However, this type of UV detection strategy can only offer semiquantitative dose information. In addition, the reported photochromic MOFs/CPs are not sensitive enough, as they often take tens of seconds or even longer to achieve color changes when exposed to UV radiation.…”

Main‐chain Macromolecular Hydrazone Photoswitches

“…Light is a powerful trigger for chemical transformations due to its traceless nature as well as the spatiotemporal control it offers. [1] Photoresponsive chemical compounds which reversibly change their configuration via isomerization and/or cyclization, such as azobenzenes, [2] stilbenes, [3] spiropyrans [4] / spirooxazines, [5] diarylethenes, [6] have frequently been integrated into photoresponsive polymeric materials. [7] Key applications of such polymers range from information encoding/data storage [8] to metal ions probing [5a] as well as photopatterning.…”