Solid Phase and Solution Phase Structural Characterization of Pyrene‐Based, T‐Shaped Molecular Dyads

Structural solid‐phase and solution‐phase properties of two pyrene‐spiropyran molecular dyads are described. Each dyad comprises a 1,1′‐[indole‐4,6‐diylbis(ethyne‐2,1‐diyl)]bis(pyrene) backbone, with the bis(pyrene) and spiropyran units adopting a T‐shaped arrangement. The strength of the C spiro –O bond is altered by replacement of H by NO 2 in the terminal aryl group of the spiropyran unit. X‐ray crystal structure determinations carried out for two of the dyads (H and NO 2 ) reveal the pyrene groups to be aligned anti to each other. The crystal packing diagrams are different; both contain pyrene π‐stacked centro‐symmetric dimers, but in one structure this is the total extent of the π stacking whereas the other structure has pyrene dimers interleaved to generate infinite parallel stacks. Detailed 1 H NOE experiments are consistent with a solution‐phase structure that differs markedly from the solid‐state structure, and in which the pyrene groups are syn to one another but orientated away from the spiropyran group. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)