Chromogenic properties of 2-(2-carbomethoxy-3,4-dichloro-6-hydroxyphenyl)benzoxazole and its Zn(II) and Cd(II) complexes

• Published in: Dyes and pigments 2020-09, Vol.180, p.108417, Article 108417
• Main Authors: Vetrova, Elena V., Tupaeva, Inna O., Sayapin, Yurii A., Gusakov, Evgeny A., Nikolaevskii, Stanislav A., Demidov, Oleg P., Minkin, Vladimir I., Metelitsa, Anatoly V.
• Format: Article
• Language: English
• Subjects: 2-(hydroxyphenyl)benzoxazole; ESIPT; Fluorescence lifetime; GSIPT; Metal-ligand complex; Photochromism; Solvatochromism
• ISSN: 0143-7208; 1873-3743
• DOI: 10.1016/j.dyepig.2020.108417

The chromogenic properties of 2-(2-carbomethoxy-3,4-dichloro-6-hydroxyphenyl)benzoxazole (1) were studied. Solvatochromism of 1 was observed at keto-enol equilibrium due to the ground state intramolecular proton transfer (GSIPT). It was found that solvents with a good hydrogen bond acceptor (β) ability were able to stabilise the keto form of 1. The excited-state intra molecular proton transfer (ESIPT) in molecules of 1 resulted in intense fluorescence with an anomalous Stokes shift of up to 8493 cm−1 and quantum yields of 0.08–0.19. The keto-form of 1 exhibits negative T-type photochromism with a thermally reversible photoconversion to the enol form. The complexes of ligand 1 with Zn(II) and Cd(II) were synthesised. According to X-ray structural analysis, the zinc complex is the neutral complex, which is formed by two oxazole-N and two phenol O donors of ligand 1 which crystallise in a centrosymmetric group with the zinc ion located on the inversion centres. The synthesised complexes possess effective blue fluorescence and resistance to photodegradation. [Display omitted] •2-(hydroxyphenyl)benzoxazole (1) possess solvatochromic properties due to GSIPT.•ASS fluorescence of 1 is due to ESIPT.•Keto form of 1 undergoes negative photochromism of T-type.•The complexes of ligand 1 with Zn(II) and Cd(II) have been synthesised.•The complexes exhibit effective blue fluorescence.