A one-pot reaction between Cu(BF4
O and 4-mercaptobenzoic acid in acetone or methanol gives rise to the formation of lamellar microcrystals of two Cu(I)-thiophenolate-based coordination polymers (CPs) with the formulas [CuCT] n (1) (CT = 4-carboxy-thiophenolate) and [CuMCT]n
(2) (MCT = 4-methoxycarbonyl-thiophenolate). Both 1 and 2 show a reversible luminescent thermochromic behavior upon cooling, changing their color from pale yellow to green to orange in the case of 1, and from pale orange to green in the case of 2. It is shown that the lamellar character of these crystals, which exhibit micrometer lateral dimensions and sub-micrometer/nanometer thicknesses, allows processing them with an organic polymer such as polyvinylidene difluoride (PVDF) to form thermochromic 1@PVDF and 2@PVDF thin films. These thermal stimuli-responsive thin films are freestanding, free of macroscopic defects, and robust under mechanical bending stress, opening up the possibility to use them in, for example, 2D imaging sensor films.
Adv. Funct. Mater.
FESEM morphological analysis for 1 and 2. a) Low-magnification image of 1 microcrystals. b) View of an individual sheet of 1 and (inset) edge view of vertically oriented crystals. c) Low-magnification image of elongated plate-like crystals of 2. d) Edge view of vertically oriented and folded 2 nanosheets, showing their flexibility.