Photochemistry of 7-Hydroxy-2-(4-hydroxystyryl)-1-benzopyrylium and Related Compounds

Abstract

2-Styryl-1-benzopyrylium derivatives exhibit deeper hues and absorption spectra that are substantially red-shifted when compared with their 2-phenyl-1-benzopyrylium analogues. They follow the same pH and light-dependent network of chemical reactions previously described for 2-phenyl-1-benzopyrylium compounds. In this work, the photochromic properties of 7-hydroxy-2-(4-hydroxystyryl)-1-benzopyrylium chloride are reported. This compound was fully characterized by UV-vis absorption, fluorescence emission, pH jumps, and flash photolysis, and its properties were compared with the analogue 7,4'-dihydroxyflavylium (7-hydroxy-2-(4-hydroxyphenyl)-1-benzopyrylium). The trans-chalcones of both compounds lacking the hydroxyl in position 2 were synthesized and used as model compounds since they exhibit cis-trans isomerization but cannot be involved in the other processes resulting from the ring closure. The transient absorption of two triplets attributed to the chalcones Ct/Ct(-), and a tautomer was detected by nanosecond flash photolysis, independent of the existence of the 2-hydroxyl substituent. The experimental results are compatible with the main formation of cis-chalcone from the singlet state. In the case of the styryl derivatives, the fraction of triplet formed from excitation of Ct is much higher, and the fraction of isomerization is much smaller. For this reason, the photochemistry of 7-hydroxy-2-(4-hydroxystyryl)-1-benzopyrylium in water is much less efficient than that of its parent 7,4'-dihydroxyflavylium; however, in the presence of CTAB micelles, intense red colors can be obtained upon irradiation, confirming the usefulness of this family of compounds as photochromic systems.

Complete resolution of the reaction Rates of flavylium Networks. The role played by 2-phenyl-2H-chromen-4-ol and the hydroxyl attack to the quinoidal Base

“…Observed rate constants for 3 different compounds: type and behavior are the same as predicted, a 4'-hydroxyflavilium compound[14], b 4'-hydroxynaphthoflavylium[15], c observed rate constant for 7-Hydroxy-2-(4-hydroxystyryl)-1-benzopyrylium chloride[16]. Reprint with permission from ref.…”

Isomerization between 2-(2,4-Dihydroxystyryl)-1-benzopyrylium and 7-Hydroxy-2-(4-hydroxystyryl)-1-benzopyrylium

“…18 However, only a few works regarding the chemistry of these compounds have so far been reported. 17,19,20 On the basis of the experimental results carried out with the compound 7-hydroxy-2-(4-methoxystyryl)-1-benzopyrylium, it was concluded that styrylflavylium compounds follow a network of chemical reactions identical to the one of flavylium compounds (Scheme 1). 17 These findings were confirmed with more detail for the compounds 7-hydroxy-2-styryl-1-benzopyrylium, 7-hydroxy-2-(4-hydroxystyryl)-1-benzopyrylium, and 7-hydroxy-2-(4-dimethylaminostyryl)-1-benzopyrylium.…”

“…17,19,20 On the basis of the experimental results carried out with the compound 7-hydroxy-2-(4-methoxystyryl)-1-benzopyrylium, it was concluded that styrylflavylium compounds follow a network of chemical reactions identical to the one of flavylium compounds (Scheme 1). 17 These findings were confirmed with more detail for the compounds 7-hydroxy-2-styryl-1-benzopyrylium, 7-hydroxy-2-(4-hydroxystyryl)-1-benzopyrylium, and 7-hydroxy-2-(4-dimethylaminostyryl)-1-benzopyrylium. 19,20 Here, we report the synthesis of 2-(2,4-dihydroxystyryl)-1-benzopyrylium chloride and the characterization of the network of chemical reactions involving this compound, the isomeric 7-hydroxy-2-(4-hydroxystyryl)-1-benzopyrylium, a common asymmetric trans-2,2′-styrylchalcone (Scheme 3) and also a common intermediate, most probably a bis(benzospiropyran).…”

A Photoelectrochemical Study of Bioinspired 2-Styryl-1-Benzopyrylium Cations on TiO2 Nanoparticle Layer for Application in Dye-Sensitized Solar Cells

“…Styrylflavylium salts 7-hydroxy-2-styryl-1-benzopyrylium tetrafluoroborate (GK1), 7-hydroxy-2-(4-hydroxystyryl)-1-benzopyrylium chloride (GK2), and 7-hydroxy-2-(4-dimethylaminostyryl)-1benzopyrylium chloride (GK4) were available from previous studies [14,15]. Compounds 7-hydroxy -2-(4-methoxystyryl)-1-benzopyrylium perchlorate (GK3) and 7,8-dihydroxy-2-(4-dimethylaminostyryl)-1-benzopyrylium hydrogensulphate (GK5) were prepared from condensation of the respective salicylaldehydes and styrylmethylketones, according to published methodology [7].…”