Beyond the Cyanine Limit:  Peierls Distortion and Symmetry Collapse in a Polymethine Dye

Theory predicts that cyanine dyes and related linear systems undergo symmetry collapse and bond localization at long chain lengths. Beyond this “cyanine limit”, the properties of these systems do not extrapolate from their shorter counterparts. To test this prediction, dipyridocyanines have been synthesized and shown to undergo such symmetry collapse with chain lengths as short as 13.