Hiding and unveiling trans-chalcone in a constrained derivative of 4 ',7-dihydroxyflavylium in water: a versatile photochromic system

作者：Pessego Marcia; Gago Sandra; Basilio Nuno; Laia Cesar A T; Jorge Parola A; Lima Joao C; Pina Fernando^*

来源：Organic and Biomolecular Chemistry, 2017, 15(2): 338-347.

DOI：10.1039/c6ob01607c

A structurally constrained derivative of 4',7-dihydroxyflavylium was studied in aqueous solution and in CTAB micelles by pH jumps, flash photolysis and continuous irradiation with spectroscopic details assessed as well by theoretical calculations. In water, up to pH = 8, the compound shows only acid base chemistry with deprotonation of the flavylium cation to form a quinoidal base that further deprotonates with pK(a)s of 4.8 and 7.4. In the basic region, unprotonated trans-chalcones are formed. No neutral transchalcone (Ct) is formed in water preventing the establishment of the well-known photochromism involving photoisomerization of this species with subsequent formation of the flavylium cation. Addition of 0.02 M CTAB drastically changes the mole fraction distribution of species, leading to the formation of Ct (chi(Ct) = 1 at pH = 5) and unveiling a photochromic behavior with a pH-tunable colour contrast in a large pH range (2 < pH < 8). The Ct species can be hidden again (irreversibly) upon addition of alpha-cyclodextrin that disrupts the CTAB micelles, reverting the system to its initial mole fraction distribution of species. These supramolecular inputs work atop the molecular reaction networks by modifying their species' mole fraction distribution.

• 出版日期2017-1-14