Synthesis of Photoresponsive Spiropyran‐Based Hybrid Polymers and Controllable Light‐Triggered Self‐Assembly Study in Toluene

Abstract

A series of polyhedral oligomeric silsesquioxane end-capped poly(spiropyran-containing methacrylate) (POSS-PSPMA) polymers, a kind of photoresponsive hybrid polymer, are synthesized via atom transfer radical polymerization. It is proved that the molecular weight of POSS-PSPMA is sharply increased by raising the proportion of methanol or the concentration of the reactants. The selfassembly behavior of POSS-PSPMA is studied in toluene: under the control of UV and visible light, POSS-PSPMA can reversibly self-assemble into aggregates because the charged merocyanines (MC) form stacks. These MC stacks act as noncovalent crosslinking points and POSS shell guarantees the stability of the aggregates. This system has a broad potential use in nanocarriers, especially for encapsulating and releasing polar substances in the nonpolar solvents. of self-assembled micellar structures bearing SP moieties. [ 13 , 18 , 19 ] As compared with the trans-cis isomerization of azobenzene, the conversion of spiropyran to charged merocyanine induces a larger increase in polarity for the core-forming block, and a large increase in polarity is a key to shift the hydrophilic-hydrophobic balance and to trigger the photocontrolled process. [ 11 , 14 , 20 ] Spiropyran-containing block copolymers can be used for self-assembly mainly because of the changes in the polarity of the spiropyran-containing block caused by photoisomerization. Matyjaszewski and coworkers [ 18 ] synthesized a block copolymer of poly(ethylene oxide)block -poly(spiropyran-containing methacrylate) (PEOb -PSPMA) by ATRP. The SPMA block underwent reversible SP/MC photoisomerization under the UV and visible light irradiation, which resulted in reversible assembling and disassembling of PEO-PSPMA. Moreover, they successfully applied this micelle system to encapsulate and release dye molecules. Ji and co-workers [ 4 ] synthesized a photo and thermo double-responsive block copolymer via ATRP using PSPMA-Br as a macroinitiator. By changing the temperature and the wavelength of the light, the core Macromol. Chem. Phys. 2013, 214, 716−725

Nanoporous frameworks exhibiting multiple stimuli responsiveness

“…4a. The intense red emission not only confirms a successful SP-MC isomerization, but also implies that the MC units within the ultraviolet-irradiated PhotoPAFs do not interact with one another; we note that MC-MC stacking leads to fluorescence quenching as reported earlier in the literature 49 , and as manifested by the properties of solid-state PhotoPAN, which, despite featuring spiropyran in the MC form without any ultraviolet irradiation, showed no measurable emission. Figure 4b shows photoswitchable fluorescence of a single particle of PhotoPAF-3.6% investigated using fluorescence microscopy (see also Supplementary Movie 4), along with a typical emission spectrum recorded on the same particle (l max ¼ 660 nm).…”

The evolution of spiropyran: fundamentals and progress of an extraordinarily versatile photochrome

“…46,[71][72][73] Notably, shielding of the spiropyran-merocyanine system from electron transfer induced by collisions with solvent molecules can also considerably improve the fluorescence intensity. 34,[74][75][76][77][78][79][80] The fluorescent dye Merocyanine 540, in which extension of the alkene bridge requires formation of an eight-membered ring to form the spiro structure, highlights the enhancement of fluorescence possible through geometric or steric constraints. 71 Partial hindrance, however, can also result in an appreciable barrier to isomerization by stabilizing the ring open form through substituents such as correctly placed electron withdrawing and Scheme 11 Photochemical ring opening through a funnel (upper) in (non-substituted) spiropyrans on the singlet manifold and (lower) via the triplet state.…”

“…An alternative to caging spiropyrans is to constrain their motion through self-assembly into nanostructures or densely packed films to enhance fluorescence. 30,[74][75][76][77]82 Kim et al, for example, recently applied Spectrally Resolved STochastic Optical Reconstruction Microscopy (SR-STORM) to solvated 6-nitro benzospiropyrans to investigate the time dependent dynamics of ring-opening and ring-closing using fluorescence on/off switching. 30 Upon simultaneous excitation of nitrospiropyran to the ring-open form at 405 nm and 560 nm excitation of nitrospiropyran to induce fluorescence or ring-closing, ringopening to the fluorescent and distinguishable TTC (l max 590 nm) and TTT (l max 635 nm) merocyanine forms was observed, with assignment based on earlier studies.…”

Spiropyran-based dynamic materials

“…The contribution of direct MC-MC interactions is also corroborated by MC fluorescence quenching which accompanies polymer aggregation. 208 Finally, the third plausible explanation is based on the photoinduced loss of the solvation layer. Spiropyran-functionalised polystyrene precipitated from a cyclohexane solution when irradiated with UV light.…”