DOI: 10.1002/chem.201100606 Hydrogen-Bonding Directed Assembly and Gelation of Donor–Acceptor Chromophores: Supramolecular Reorganization from a Charge-Transfer State to a Self-Sorted State Anindita Das, [a] Mijanur Rahaman Molla, [a] Ambar Banerjee, [b] Ankan Paul, [b] and Suhrit Ghosh* [a] Gelation [1] of various func- tional p systems [2] has been ex- tensively studied due to the possibility of modulating their photophysical properties in the gel state. Donor–acceptor (D– A) charge-transfer (CT) inter- actions have been utilized to generate many elegant supra- molecular materials, such as ro- taxanes and catenanes, [3] syn- thetic ion channels, [4] liquid crystals, [5] folded oligomers, [6] polymers, [7] and organogels. [8] Recently we have demonstrated self-sorting [9] in a mixed assem- bly of a bisACHTUNGTRENNUNG(amide)-functionalized dialkoxynaphthalene (DAN) donor and a naphthalenediimide (NDI) acceptor due to synergistic effect of hydrogen bonding and p stack- ACHTUNGTRENNUNGing. [10a] 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 D–A chro- mophore could also be achieved. However, in the previously reported D–A pair (DAN-2 + NDI-0), [10a] although a CT band was visible in solution, no gelation could be observed, probably due to highly rigid assembly of NDI chromophor- e. [10b] 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 addi- tional methylene units. In this communication we reveal CT- interaction-mediated gelation of this D–A pair in a moder- ately nonpolar solvent tetrachloroethylene (TCE) and also demonstrate the serendipitous discovery that when the sol- vent was changed to a less polar methylcyclohexane (MCH), the CT gel switched over to thermodynamically stable self- sorted gel within few hours. Self-assembly of NDI-2 + DAN-4 (1:1, total concentra- tion = 25 mm) was performed in TCE. The compounds were soluble only at elevated temperature to generate a colorless solution, which when cooled down to room temperature produced a deep red gel (Figure 1a) clearly suggesting alter- nate co-stacking of the donor and acceptor chromophores. NDI-2 and DAN-4 individually also showed spontaneous ge- lation under identical conditions (Figure 1). [a] A. Das, M. R. Molla, Dr. S. Ghosh Indian Association for the Cultivation of Science Polymer Science Unit 2A & 2B Raja S. C. Mullick Road, Kolkata 700032 (India) Fax: (+ 91) 33-2473-2805 E-mail: psusg2@iacs.res.in [b] A. Banerjee, Dr. A. Paul Indian Association for the Cultivation of Science Raman Center for Atomic, Molecular and Optical Sciences 2A & 2B Raja S. C. Mullick Road, Kolkata 700032 (India) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201100606. Scheme 1. Structure of various donor and acceptor building blocks. Figure 1. Left: SEM picture of the CT-gel (1:1 mixture of NDI-2 + DAN-4) in TCE; Right: Photographs of gels in TCE derived from a) NDI-2 + DAN-4 (1:1), b) NDI-2, c) DAN-4, d) NDI-2 + DAN-2. Total ge- lator concentration = 25 mm in each case. Chem. Eur. J. 2011, 17, 6061 – 6066  2011 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim 6061 COMMUNICATION