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Tuning the Negative Photochromism of Water-Soluble Spiropyran Polymers
journal contribution
posted on 2018-09-21, 20:14 authored by Matthew
J. Feeney, Samuel W. ThomasIn aqueous media,
negative photochromism can occur from cationic,
protonated merocyanines (MCH+) to spiropyrans (SP) upon
exposure to visible light. Herein, we demonstrate the uniquely simple
manner in which polymers can tune the key properties of these photochromes
through copolymer preparation. Nine water-soluble, SP-containing polymers
yield wide ranges of key properties for negative photochromismaccessible
MCH+ pKa values spanning 5
pH units, quantum yields of photochemical ring closure up to 0.2,
and rates of thermal equilibration ranging 2 orders of magnitude.
In buffered solutions, many of these polymers showed photostationary
states with greater than 80% conversion to SP and no detectable photochromic
fatigue over 15 cycles. These results demonstrate the potential for
tuning key properties of the MCH+ photochrome through both
the spiropyran pendants themselves and the water-solubilizing comonomers.
The dependence of MCH+ pKa on
comonomer structure enabled tunable range of pH for reversible photoacid
activity using a single spiropyran derivative, further showcasing
the versatility of water-soluble photochromic polymers.