Proposers : this project is submitted jointly by a team of the Institut Charles Sadron in Strasbourg and one of the Indian Association for the Cultivation of Science in Kolkata. This collaboration and the proposed subject were initiated during a 3 months stay of the Indian PI as a visiting professor in the French team and will be part of an International Associated Lab. Field of research : This proposal aims at studying self-assemblies of p-(Donor) and n-(acceptor) type pi-conjugated systems functionalized by H-bonding groups and understanding the parameters that lead them to segregate or not. Context : Co-assembly of p-(Donor) and n-(Acceptor) type pi-conjugated semiconductors are of enormous importance for their applications in organic electronic device. Donor (D) and acceptor (A) type chromophores often self-assemble in alternate stacking (AD)n owing to ground state Charge Transfer (CT) interaction. This trend can be overcome by functionalizing them with H-bonding groups. Indeed, one of the proposers has developed compounds with donors (D) or acceptors (A) pi-systems bearing two H-bonding groups (G) via variable lengths spacers (G—A—G and G—D—G). When pairs of A and D compounds have different distances between both groups G, their mixtures yield segregated self-assemblies (A)n+(D)n. However, the structures of the segregated self-assemblies are still unknown due to the lack of X-ray structures. When the distances between the H-bonding groups in A and D match, A/D mixtures first yield alternate self-assemblies, (AD)n. Then, depending on the solvent, they may reorganize into a segregated state. We will take advantage of this unprecedented property to understand not only the structure of these systems but also their dynamic. Objectives : we propose to study the self-assembly of dialkoxynaphthalene (DAN) and naphthalene-diimide (NDI) (resp. donor and acceptor) functionalized by H-bonding groups. The goals are : • to understand the role of H-bonds in the mode of co-assembly (alternate or segregated) and in the shape of the self-assemblies; • to identify the molecular parameters that govern the co-assembling mode or its reorganization (strength and number of H-bonds); • to understand the role of the solvent, especially when reorganization occurs; • to find and optimize the conditions to obtain solid state films with the same structures and photophysical properties as in solutions; these films will be oriented and the self-assemblies studied by electron diffraction. The charge mobility will be measured in relation with the morphology of the aggregates. Methods : we will vary the molecular parameters (by chemical synthesis) and the physicochemical parameters (C, T, quality of the solvent); then we will study the structure of the resulting self-assemblies of A, D and A/D mixtures in each condition. The distances between the H-bonding groups in A and D compounds will be tuned to allow both possible assemblies (DA)n or segregated assemblies (D)n and (A)n. In order to vary the molecular parameters, we will synthesize analogues with urea and amides to vary the strength of the H-bonds; analogues with 1 or 2 H-bonding groups to release the constraint imposed by 2 bonds; analogues with hydrophilic groups to self-assemble them in water. The structures will be studied as follows : the mode of co-assembly (alternate CT or segregated) will be determined by UV spectroscopy and photoluminescence ; the nature, number and strength of the H-bonds will be identified by VT-FT-IR spectroscopy. DSC and ITC measurements will be performed to quantify the intensities of the global interactions. The shape and size of the aggregates will be measured by TEM and by SAXS. We will form films with the same self-assemblies as in solution, and we will orient them to study their structures by electron diffraction. Electron mobility will be measured in the films.