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Heli(aza)cene: A Helical Molecular Tweezer with Tunable Intra‐ and Intermolecular Charge Transfer
Author(s) -
Kumar Rajesh,
Semwal Shrivats,
Choudhury Joyanta,
Srivastava Aasheesh
Publication year - 2017
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201703781
Subject(s) - intermolecular force , intramolecular force , stacking , chemistry , crystallography , molecule , hydrogen bond , amide , crystal (programming language) , stereochemistry , organic chemistry , computer science , programming language
Non‐planar fluorophores offer unique avenues of intra‐ and intermolecular energy transfer not available in their planar counterparts. We have rationally designed a molecular tweezer based on the pyridine‐2,6‐dicarboxamide framework having two structurally similar arms with extended π‐surface. We termed this molecular tweezer as Heli(aza)cene ( HAC ) due to its spontaneous adoption of helical conformation stabilized by the amide and imine moieties present in it. In the helical conformation, the two arms of HAC are twisted unequally. This asymmetry confers dissimilar electronic character to the two arms and results in intramolecular charge transfer interactions in HAC . Homochiral stacking of the P‐ and the M‐ helices in crystal, and profound redshifting of the emission at higher concentrations of HAC was attributed to intermolecular charge‐transfer interactions in aggregated/crystal state. Exposure of HAC , in solution as well as in the solid state, to Lewis/Brønsted acids results in rapid and vibrant color changes. This is the first example of a π‐layered helical molecule exhibiting tunable intra‐/intermolecular charge‐transfer characteristics.