Synthesis of Some New Substituted Photochromic N,N′-Bis(spiro[1-benzopyran-2,2′-indolyl])diazacrown Systems with Substituent Control over Ion Chelation

The reversible photochemical ion chelation of the newly synthesised substituted N,N′‐bis(spiro[1‐benzopyran‐2,2′‐indolyl])diazacrown systems 15a–c and the subsequent molecular electronic control of this process using appropriately placed substituent groups on the spiro‐benzopyran skeleton is reported. The principle of molecular electronic control of ion chelation is demonstrated by comparing the behaviour of the newly synthesised nitro‐substituted and pyrido‐annulated spiro‐benzopyran system 9b with that of the unsubstituted compound 9a. Electronic substituent control over ion chelation is then exemplified for the new N,N′‐bis(5′‐nitrospiro[1‐benzopyran‐2,2′‐indolyl])diazacrown system 15c and further exemplified for the corresponding 5′‐trifluoromethyl derivative 15b, which contains the photochemically more robust trifluoromethyl group. The crown system 15a, unsubstituted in the spiro‐indole moiety, is also reported. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)