Hydrogen-Bonding Directed Assembly and Gelation of Donor-Acceptor Chromophores: Supramolecular Reorganization from a Charge-Transfer State to a Self-Sorted State

Gelation[1] of various functional π systems has been extensively studied due to the possibility of modulating their photophysical properties in the gel state. Donoracceptor (D-A) charge-transfer (CT) interactions have been utilized to generate many elegant supramolecular materials, such as rotaxanes and catenanes, synthetic ion channels, liquid crystals, folded oligomers, polymers, and organogels. Recently we have demonstrated self-sorting in a mixed assembly of a bisACHTUNGTRENUNG(amide)-functionalized dialkoxynaphthalene (DAN) donor and a naphthalenediimide (NDI) acceptor due to synergistic effect of hydrogen bonding and π stack- ACHTUNGTRENUNGing. Control experiments indicated that if the number of methylene groups (n) between the DAN/NDI chromophore and the amide functionality can be adjusted so that n-NDI= (n+2)-DAN, then alternate co-stacking of the DA chromophore could also be achieved. However, in the previously reported D-A pair (DAN-2+NDI-0), although a CT band was visible in solution, no gelation could be observed, probably due to highly rigid assembly of NDI chromophore. Thus to achieve CT gelation we have explored a new D-A pair DAN-4+NDI-2 (Scheme 1) in which the rigidity of the acceptor unit is reduced due to the inclusion of additional methylene units. In this communication we reveal CTinteraction- mediated gelation of this D-A pair in a moderately nonpolar solvent tetrachloroethylene (TCE) and also demonstrate the serendipitous discovery that when the solvent was changed to a less polar methylcyclohexane (MCH), the CT gel switched over to thermodynamically stable selfsorted gel within few hours © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.