Synthesis and characterization of new spiropyran micrometer-sized photochromic fluorescent polymeric particles of narrow size distribution by a swelling process

Photochromic fluorescent uniform micrometer-sized particles were prepared in two ways: (1) Swelling of polystyrene (PS) and poly(styrene-butylmethacrylate) (P(S-BMA)) template particles with spiropyran dye (FSP) to obtain PS/FSP and P(S-BMA)/FSP uniform particles; (2) A similar swelling process, replacing FSP by AIBN, styrene and a spiropyran monomer (MSP), followed by co-polymerization of the monomers within the swollen microspheres to obtain P(S-BMA)/P(S-MSP) uniform particles. The spiropyran dyes are not fluorescent in water or in non-polar organic solvents. In contrast, the dyes encapsulated within the particles exhibit strong red fluorescence in the merocyanine conformation. Fluorescence measurements reveal that the P(S-BMA)/FSP microspheres exhibit higher fluorescence than the PS/FSP particles. The microspheres aqueous dispersion was exposed to alternate UV and visible light cycles and it was found that the fluorescence intensity of the PS/FSP and the P(S-BMA)/FSP particles decreased by 30% of its original value after 5 photoswitching cycles while that of the P(S-BMA)/P(S-MSP) particles remained the same.