Preparation of spiropran containing materials and determination of light sensitivity, photochromic and mechanochromic properties

In this study, methacrylated spiropyran (mSP) monomer and dimethacrylated spiropyran crosslinker (dimSP) were synthesized using 2-(3',3'-Dimethyl-6-nitrospiro [chromene-2,2'-indole]-1' (3'H) -yl) ethanol (spiropyran, SP) molecule. Then, poly(methacrylated spiropyran) [poly(mSP)] brushes on silicon disc and on silicon microparticle surfaces using mSP monomer, and poly(2-hydroxy ethyl methacrylate) [poly (HEMA)] gels using dimSP crosslinker were prepared. Poly(mSP) brushes were synthesized by interface-mediated RAFT polymerization on a silicon disc surface. The grafting density (σ, chain nm-2) and distance between grafting points (D, nm) of these brushes were found as σ=0,56 chain nm-2 and D=1,52 nm, respectively. It was observed that the surface was quite homogeneous and the rms (root-mean-square) value was about 2.66 nm, using atomic force microscope. The poly(mSP) form was transformed into the merocyanine (MC) isomer [poly(mMC)] using ultraviolet (UV) light. This process was converted back into the poly(mSP) isomer using visible light (Vis). These isomerizations were followed by water contact angle measurements. Surface energy components of these isomers were calculated using the contact angle data measured with various liquids in the Van Oss - Good equation. The electron acceptor and electron donor surface free energies of SP and MC form of P(MMASP) brushes were found as γs + =0,47 mJ m-2 , γs - =1,15 mJ m-2 and γs + =0,85 mJ m-2 , γs - =10,25 mJ m-2 , respectively. It is concluded that MC form of P(MMA-SP) brushes possess high base character; whereas, SP forms have low base character. Photochromic hybrid poly(mSP) brushes were synthesized by interface-mediated RAFT polymerization on silicon microparticle surface. Structural characterization and surface morphology of these photochromic hybrid brushes were performed by GA-FTIR spectroscopy and Scanning Electron Microscopy (SEM), respectively. The colorless poly(mSP) isomer of the photochromic hybrid microparticles suspended in dimethylformamide (DMF) was transformed into the merocyanine (MC) isomer [poly(mMC)] by UV light at 7 min, and it was converted back into the poly(mSP) isomer by Vis light at 9 min. Finally, mechanochromic poly(HEMA) gel was prepared using dimSP crosslinker. Its mechanochromic state was determined by mechanical stress-strain mesauments and swelling test in DMF. In these tests, the yellow poly(HEMA) gel resulting from the SP isomer was appeared as white coloured due to the transformation into the MC isomer formed during swelling or elongation.