A new method for the preparation of solvatochromic 5-(5-X-6-hydroxynaphthyl-2)-7H-indolo[1,2-a]quinolinium merocyanines

A new method for the preparation of 7H-indolo[1,2-a]quinolinium solvatochromic dye precursors has been investigated. 5-(6-Hydroxynaphthyl-2)-7,7-dimethyl-7H-indolo[1,2-a]quinolinium perchlorate, 5-(5-bromo-6-hydroxynaphthyl-2)-7,7-dimethyl-7H-indolo[1,2-a]quinolinium perchlorate and 5-(5-nitro-6-hydroxynaphthyl-2)-7,7-dimethyl-7H-indolo[1,2-a]quinolinium perchlorate were obtained via demethylation of the corresponding 5-(5-X-6-methoxynaphthyl-2)-7,7-dimethyl-7H-indolo[1,2-a]quinolinium salts. The application of pyridinium hydrochloride in the demethylation of the methoxy perchlorates allowed to obtain the products with the almost quantitative yield in a very short time, especially when the reaction was carried out using microwave irradiation.