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Tailoring effects of the chain length and terminal substituent on the photochromism of solid-state spiropyrans.

Recently, by constructing a haloalkyl chain, a new class of solid-state spiropyrans showing advanced photochromic activity has been developed, but the tailoring effect of the haloalkyl chain on photochromism is unclear. Here, the photochromism of solid-state spiropyrans with different chain lengths and end substituents is investigated, which gives a clear correlation between the chain length/end substituent and the thermodynamic stability of zwitterionic merocyanine. This work provides a useful designing strategy for tailoring the photochromism of solid-state spiropyrans.