Formation of a leuco Spirolactone from 4‐(2‐Carboxyphenyl)‐7‐diethylamino‐4′‐dimethylamino‐1‐benzopyrylium: Design of a Phase‐Change Thermochromic System Based on a Flavylium Dye

Abstract

A phase-change thermochromic system was designed through the reversible transformation of the 4-substituted flavylium dye 4-(2-carboxyphenyl)-7-diethylamino-4'-dimethylamino-1-benzopyrylium into its leuco form, in the presence of a developer (ethyldiisopropylamine) and a suitable solvent (e.g., acetonitrile, n-pentadecanonitrile). The leuco form of the flavylium-based dye is a spirolactone species whose ring opens at low temperature (below the solvent melting point) to form the blue flavylium cation. Decarboxylation of the lactone to give 4-phenyl-7-diethylamino-4'-dimethylamino-1-benzopyrylium was observed upon irradiation of the system with UV light, erasing the thermochromic effect.

Chemistry and applications of flavylium compounds: a handful of colours

“…165,166 4-(2-Carboxyphenyl)-7-diethylamino-4 0 -dimethylaminophenyl-1-benzopyrylium, I in Scheme 32, was shown to have the same Scheme 32 Chemical network of 4-(2-carboxyphenyl)-7-diethylamino-4 0 -dimethylaminophenyl-1-benzopyrylium. 167 type of equilibrium. 167 The carboxyl group can attack carbon 4, forming a lactone ring, II in Scheme 32, and the resulting molecule is similar to triarylmethane derivatives.…”

A colorimetric and fluorogenic probe for bisulfite using benzopyrylium as the recognition unit

“…It has been reported that the C‐4 atoms of the benzopyrylium unit are prone to attack by nucleophiles . Thus, we hypothesized that nucleophilic attack of HSO 3 − toward the benzopyrylium C‐4 atom disturbs the π‐conjugation of probe CB and recovery of the coumarin moiety fluorescence.…”

“…It has been reported that the C-4 atoms of the benzopyrylium unit are prone to attack by nucleophiles. [26] Thus, we hypothesized that nucle- 623.1983) ( Figure S4). These data are strongly support the proposed sensing mechanism shown in Scheme 1.…”

“…Recently, benzopyrylium‐based dyes have received great attention due to their good photochemical properties, such as high molar extinction coefficients, large fluorescence quantum yields, and long excitation and emission wavelengths . More significantly, the benzopyrylium unit can act as a guest receptor, as its C‐2 and C‐4 atoms are both liable to attack by nucleophiles, thus altering the large π‐conjugated system of the dye and thereby affording remarkable blue shifts in the optical spectra of the sensing system. Based on this mechanism, fluorescent probes for Cys/Hcy, H 2 S, SO 2 , HClO, Hg 2+ , H 2 O 2 and peroxynitrite have been reported.…”

“…Several fluorescent probes for bisulfite have been constructed based on the nucleophilic reaction with aldehyde, [9][10][11][12][13] deprotection of levulinate, [14,15] Michael addition reaction, [16][17][18][19][20][21][22] extinction coefficients, large fluorescence quantum yields, and long excitation and emission wavelengths. [23][24][25] More significantly, the benzopyrylium unit can act as a guest receptor, as its C-2 and C-4 atoms are both liable to attack by nucleophiles, [26] thus altering the large πconjugated system of the dye and thereby affording remarkable blue shifts in the optical spectra of the sensing system. Based on this mechanism, fluorescent probes for Cys/Hcy, [27] H 2 S, [28][29][30] SO 2 , [31] HClO, [32] Hg 2+ , [33] H 2 O 2 [34] and peroxynitrite [35] have been reported.…”