Photoswitchable Organic Nanofibers (original) (raw)
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Macromolecules, 2020
Covalent bonding of photochromic molecules to a polymer matrix, flexibility of the polymeric host, and also its nanofibrous state are appropriate conditions to enhance the switching rate, photofatigue resistance, sensitivity, and long-term performance of these photo-active groups. Herein, photoresponsive polymethyl methacrylate and poly(methyl methacrylate-cobutyl acrylate) chemically modified with spiropyran (MSP and MBSP, respectively) were prepared through emulsion polymerization. To improve photosensitivity and reduce response time, the corresponding nanofibers (MSP@NF and MBSP@NF) were prepared by an electrospinning technique. Smooth and beadless morphology, high porosity (above 85%), and uniform diameter size distribution of MSP@NF (169 ± 39 nm) and MBSP@NF (203 ± 47 nm) were identified. Time-dependent UV−vis spectra and photo-isomerization kinetics revealed that flexible MBSP@NF has remarkable enhancement in the SP to merocyanine isomerization rate (19 folds) relative to the corresponding film. Reversible responsivity to HCl and ammonia vapors showed a dramatic color change and maximum absorption peak displacement for nanofiber samples immediately, together with fluorescence switching "on" and "off", while this took about 10 min for the MBSP@F sample. This was attributed to the high surface area and porous structure of these nanofibers, providing enhanced diffusion and interaction with the photo-active groups. Reversible optical write−erase cycles with improved response time and color intensity approved photopatterning capability of MBSP@NF. Enhanced photochemical, photostability, and photofatigue resistance of MBSP@NF within 10 cycles of alternating exposure to HCl−ammonia vapors and also UV−vis irradiations revealed the potentiality of such nanofibers in visual reversible photopatterning and optochemical acidochromic and ammonia-chromic portable probes.
European Polymer Journal, 2017
Spiropyran derivatized vinylic monomer (MSP) was prepared by coupling a typical spiropyran dye, 1′-(2-hydroxyethyl)-3′,3′-dimethyl-6-nitrospiro(2H-1-benzo-pyran-2,2′-indoline), to methacryloyl chloride. Poly(styrene-butylmethacrylatedivinylbenzene-MSP), P(S-BMA-DVB-MSP), photochromic fluorescent nanoparticles (NPs) of narrow size distribution were prepared by emulsion polymerization of the vinylic monomers: S, BMA, DVB and MSP. The influence of various polymerization parameters (e.g., concentration of the monomers, initiator and surfactant and pH) on the diameter, diameter distribution and photochromic fluorescence properties of the particles was elucidated. Spiropyran type molecules as well as MSP are colorless and non-fluorescent at the Spiro conformation. These compounds at the Merocyanine conformation are nonfluorescent in water or in non-polar organic solvents. However, when the Merocyanine conformation is entrapped within hydrophobic polymer particles, the particles exhibit blue color and strong red fluorescence. Absorbance and fluorescence measurements reveal that increasing the MSP or BMA relative concentration leads to a higher absorbance and fluorescence intensity of the formed P(S-BMA-DVB-MSP) NPs. Photoisomerization switching of the P(S-BMA-DVB-MSP) NPs was studied by exposing the NPs aqueous dispersion to alternating UV and visible light cycles. This study indicates 100% reversibility after five cycles of photoswitching.
The Journal of Physical Chemistry, 1995
photomirocyanines have rather high first-order hyperpolarizabilities, this photo-orientation leads to secondirarmonic generation (SHG). The second-order susceptibility dg: of PMMA films doped with Gnitro-l',3',3'trimethylspiro[2f/-1-benzopyran-2,21indolise1(25Vo Ww) has been measured at 10 pm/V. If a PMMA film doped with spiropyran and preoriented by corona poling at 90 oC is irradiated in the UV, an SHG signal of photomerocyanine is also observed as a result of a memory effect of the orientation of spiropyran molecules. The photoswitching of this nonlinear optical property can be inverted by visible light irradiation. Only paltially reveisible switching is observed because of a gradual light-induced disorientation of photomerocyanine dipoles.
Molecular switching in nano-structured photochromic films of biopolymers
Materials Science and Engineering: C, 2003
This paper reports the investigation of the photochromic and conformational behaviour of a poly (L-glutamic acid) (PSG) chemically modified with 85% spiropyran units in the side chains, PSG. We preliminary studied the behaviour of PSG in solution and then we performed a characterisation of the polymer in bidimensional systems. PSG monolayer at the water -air interface was characterised by means of surface pressure -molecular area isotherms and UV -Vis Spectroscopy and the photochromic behaviour was illustrated. Moreover, we transferred, by means of the Langmuir -Blodgett (LB) technique, polypeptide monolayers onto solid support in order to obtain ordered and nano-organized systems whose spectroscopic properties were investigated. D
The photochromism of spiropyrans bound on side-chains of soluble polymers
European Polymer Journal, 1981
The effect was investigated of the distance of the photochromic ce ltre of 5'-aminomethyll',3',3'-trimethyl-6-nitrospiro[2H-l-benzopyran-2,2'-indoline] from the methyl methacrylate chain on the kinetics of the discolouration process. The centre was bound through an amide bond on side-chains consisting of various numbers of methylene groups of ~-amino acids. The thermal discolouration of acetone solutions followed first-order kinetics. Elongation of the side-chain on which the spiropyran unit was bound caused an increase in the thermal discolouration rate. In nonpolar solutions, an effect of polar centres of the polymer chain was superimposed on the dependence.