A sultone‐based reversible dark red‐yellow conversion thermochromic colorant with adjustable switching temperature

Abstract

A reversible, adjustable thermochromic colorant with bichromatic conversion from dark red (cool state) to yellow (heat state) was prepared using bromocresol purple (BCP) as colour former. The thermochromic behaviour of this colorant was investigated during the heating‐cooling cycle, including the colour depth, colour difference and switching temperature. The mechanism of thermochromic colorant switching between dark red and yellow originated from the transformation of the conjugated structures of BCP, which was confirmed by infrared spectrometry. The switching temperature can be flexibility adjusted between 13–46 °C by mixing solvents according to Schröder's equation, which was demonstrated by differential scanning calorimetry measurement. The thermochromic colorant presented good reversible thermochromic performance with stable changes in colour parameters for 50 heating‐cooling cycles. This sultone‐based reversible dark red‐yellow conversion thermochromic colorant is suitable for application as thermal‐indicating material under various conditions.

A nontoxic reversible thermochromic binary system via π–π stacking of sulfonephthaleins

“…Further evidence of the CPR structure in our binary thermochromic system comes from FTIR analysis ( Figure S4 of Supporting Information). FTIR measurements indicated that the binary system of CPR-TD (10 mol%) at both hot liquid (70 °C) or cool solid (25 °C) showed similar peaks attributed to the sulfone group at 1345 and 1191 cm −1 which indicates a ring-closed CPR structure 21 at both temperatures and different colours. After treatment with base however, peaks at 1180 and 1630 cm -1 due to the benzene sulphonate and p-quinoid groups respectively appear 53,54 which are consistent with the ring opened structure of CPR.…”

“…20 Recently, they have been used to fabricate thermochromic systems, for example, one sulfonephthalein dye (bromocresol purple) was used as a colour former in a three-component thermochromic system, in which stearic acid was the developer and long-chain Please do not adjust margins Please do not adjust margins alcohols were described as solvents with the reversible ringopening mechanism similar to that of the leuco dye system. 21 π-π stacking, a non-covalent interaction between molecules, has been reported to be the source of reversible thermochromism in conjugated polymers 22,23 and crystals [24][25][26] . It has also been used to explain colour changing phenomenon of aggregachromic dyes with highly conjugated planar structures 9,27 , such as triphenylenes 28 and perylene bisimides 29 , which form dimers or other agglomerates in solution with an increase in dye concentration.…”