DOI: 10.1002/chem.201201140 Hydrogen-Bonding Induced Alternate Stacking of Donor (D) and Acceptor (A) Chromophores and their Supramolecular Switching to Segregated States Anindita Das, [a] Mijanur Rahaman Molla, [a] Bholanath Maity, [b] Debasis Koley,* [b] and Suhrit Ghosh* [a] Introduction Self-assembly of p-conjugated chromophores [1] has emerged as an exciting area of research on its own right due to close relevance to applications in organic electronic devices. [2] Various chromophoric building blocks [3] have been explored to construct organized supramolecular assemblies with hier- archical structures for achieving desired photophysical [4] and transport [5] properties, which could not have been realized in their monomeric form. Instead of a single building block, mixed assembly of multiple chromophores [6] is even more in- teresting because it provides additional opportunities for supramolecular engineering to dictate the spatial organiza- tion of one chromophore with respect to the other, which in turn governs the photophysical properties of the resulting assembled material. In this context donor (D)–acceptor (A) charge-transfer (CT) complexes have been studied with great interest for a long time. [7] Supramolecular systems based on D–A CT interactions include folded oligomers [8] and polymers, [9] supramolecular gels, [10] mesogens, [11] super- amphiphiles, [12] ordered macromolecules, [13] rotaxanes, [14] cat- enanes, [15] and synthetic ion channels. [16] Association con- stants for such CT complexes have been estimated to be weak [7] in most cases or at the best moderate even for the most appropriate D–A pairs. Thus, in most of the above- mentioned systems self-assembly with appreciable stability could be achieved only by reinforcing the CT complex with Abstract: This paper reports compre- hensive studies on the mixed assembly of bis-(trialkoxybenzamide)-functional- ized dialkoxynaphthalene (DAN) donors and naphthalene-diimide (NDI) acceptors due the cooperative effects of hydrogen bonding, charge-transfer (CT) interactions, and solvophobic ef- fects. A series of DAN as well as NDI building blocks have been examined (wherein the relative distance between the two amide groups in a particular chromophore is the variable structural parameter) to understand the struc- ture-dependent variation in mode of supramolecular assembly and morphol- ogy (organogel, reverse vesicle, etc.) of the self-assembled material. Interest- ingly, it was observed that when the amide functionalities are introduced to enhance the self-assembly propensity, the mode of co-assembly among the DAN and NDI chromophores no longer remained trivial and was dictat- ed by a relatively stronger hydrogen- bonding interaction instead of a weak CT interaction. Consequently, in a highly non-polar solvent like methyl- cyclohexane (MCH), although kineti- cally controlled CT-gelation was initial- ly noticed, within a few hours the system sacrificed the CT-interaction and switched over to the more stable self-sorted gel to maximize the gain in enthalpy from the hydrogen-bonding interaction. In contrast, in a relatively less non-polar solvent such as tetra- chloroethylene (TCE), in which the strength of hydrogen bonding is inher- ently weak, the contribution of the CT interaction also had to be accounted for along with hydrogen bonding lead- ing to a stable CT-state in the gel or so- lution phase. The stability and mor- phology of the CT complex and rate of supramolecular switching (from CT to segregated state) were found to be greatly influenced by subtle structural variation of the building blocks, solvent polarity, and the DAN/NDI ratio. For example, in a given D–A pair, by intro- ducing just one methylene unit in the spacer segment of either of the build- ing blocks a complete change in the mode of co-assembly (CT state or seg- regated state) and the morphology (1D fiber to 2D reverse vesicle) was ob- served. The role of solvent polarity, structural variation, and D/A ratio on the nature of co-assembly, morphology, and the unprecedented supramolec- ular-switching phenomenon have been studied by detail spectroscopic and mi- croscopic experiments in a gel as well as in the solution state and are well supported by DFT calculations. Keywords: charge-transfer · donor– acceptor systems · gels · hydrogen bonds · self-assembly [a] A. Das, M. R. Molla, Dr. S. Ghosh Polymer Science Unit Indian Association for the Cultivation of Science 2A & 2B Raja S. C. Mullick Rd. Kolkata-700032 (India) Fax: (+ 91) 33-2473-2805 E-mail: psusg2@iacs.res.in [b] B. Maity, Dr. D. Koley Chemical Science Division Indian Institute of Science Education and Research Kolkata, 741252 (India) E-mail : koley@iiserkol.ac.in Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201201140. Chem. Eur. J. 2012, 18, 9849 – 9859  2012 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim 9849 FULL PAPER