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)