Selective [2 + 2]-Cycloaddition in Methacrylic Stilbene Polymers without Interference from E/Z-Isomerization

Abstract

Stilbene is known to undergo two different reactions upon photochemical excitation. The first is an E/Z isomerization and the second is a [2 + 2]-cycloaddition of two stilbene molecules. Because both reactions occur in parallel their use is limited. Here we report on photorefractive polymers with a methacrylate backbone and covalently attached 4-hydroxy-(E)-stilbene or 3,5-dimethoxy-4-hydroxy-(E)-stilbene units in the side chain which show [2 + 2]-cycloaddition only. Both polymers, poly(4-methacryloyloxy-(E)-stilbene) (PMAES) and poly(4-methacryloyloxy-3,5-dimethoxy-(E)-stilbene) (PMADMES), show very high initial refractive indices of 1.6533 for PMAES and 1.6288 for PMADMES. The photochemical reaction upon laser irradiation with 355 nm was monitored by UV/vis, fluorescence, and IR spectroscopy. The light-induced changes of the refractive index at 633 nm measured by surface plasmon resonance (SPR) were found to be Δn > 0.05 for PMAES and Δn > 0.04 for PMADMES. The sensitivity of PMADMES is enhanced compared to PMAES due to the electron donating groups (EDG) as the direct comparison of both polymers shows. Both polymers are useful for optical devices because they do not show any absorption in the visible range and are noncrystalline as determined by wide-angle X-ray scattering (WAXS) and differential scanning calorimetry (DSC).

Wavelength‐Dependent Stiffening of Hydrogel Matrices via Redshifted [2+2] Photocycloadditions

“…While their study demonstrates the potential of photocycloadditions in engineering biomaterial properties for in vitro cell study, certain cell types—such as hepatic stellate cells24—are not resistant toward the applied UV light. However, in the field of soft matter materials, the majority of studies on photocycloadditions are carried out on stilbene,25,26 coumarin,27–29 thymine,30,31 and cinnamic acid32 derivatives, which require activation by short wavelength UV light (note that we are referring exclusively to the bond forming photocycloaddition of coumarin, in the context of bond cleavage short wavelength blue light has been successfully used for coumarin‐based photocages) 33. To overcome limitations of applicability in biology‐related systems from UV light exposure,34 and broaden the synthetic toolbox of orthogonally addressable photoligation reactions,21,35,36 the development of redshifted photocycloadditions is key 37…”

Green light triggered [2+2] cycloaddition of halochromic styrylquinoxaline—controlling photoreactivity by pH

“…Amongst photochemical reactions, [2+2] cycloadditions have key advantages such as λ-orthogonal reversibility, wavelengthdependent reactivity and lack of any additives [30][31][32][33][34][35] . Combining these advantages with the ease of functionalizing photoreactive groups, several chromophores with redshifted reactivity (up to 470 nm) such as styrylpyrene 30,32 and acrylamidylpyrene 36 have been introduced by our group and their applications in soft matter design are being actively exploited 30,36,37 .…”

Efficiency of [2 + 2] photodimerization of various stilbene derivatives within the DNA duplex scaffold

“…In contrast, 4 | J. Name., 2012, 00, [1][2][3] This journal is © The Royal Society of Chemistry 2012 homodimer aggregates of both S A and S D did not undergo photodimerization reaction at all; their quantum yields were nil. Thus, quantum yields of homo-photodimerization are highly dependent on substituents.…”

“…1 This photodimerization is used for the synthesis of cyclobutane derivatives, in polymer syntheses, and in crosslinking. 2,3 The effects of concentrations 4 and solvents 5,6 on photodimerization of stilbenes have been evaluated and reactivities of several stilbene derivatives have been investigated. 7 However, since most photo-cycloadditions are conducted under conditions in which stilbene monomers are dispersed in solvent, molecules must form an aggregate (or a cluster) prior to the photoreaction.…”