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The current work describes the Michael addition (MA) reaction between amine group appended NDI derivatives and α,β-unsaturated ketones (chalcones) with an aim to tune the optical and electrochemical properties of NDI derivatives via an easy and scalable synthesis method. Two NDI derivatives having aromatic (1) and aliphatic (2) amine N-imide substituents were synthesized and further used for the synthesis of MA products. The products were evaluated for their optical, electrochemical and transport properties. Aggregation behavior of the molecules was studied and established by absorption and emission spectroscopy. It is observed that NDIs and their respective MA derivatives (3 and 4) show strong aggregation behavior. Most interestingly the HOMO–LUMO energy levels in MA products were uplifted which is generally not achieved by imide-N substitutions. The driving force for intramolecular electron transfer was calculated from their first oxidation and reduction potentials indicating the formation of charge separated states. MA products also showed improved electron mobility compared to their NDI precursors. Intramolecular charge transfer interaction was established by fluorescence and femtosecond transient absorption spectroscopy (TAS). The materials have been studied for their use as electron transport layer (ETL) materials in inverted organic solar cells and an efficiency of 3% has been obtained. Overall, Michael addition reaction on NDI has resulted in effective tuning of optical properties, energy levels and transport properties without involving tedious multistep core substitution reactions. [ABSTRACT FROM AUTHOR]

• D-A-D triads type molecules synthesized using perylenediimde (PDI) bonded with naphthalenediimide (NDI) units via aliphatic (Triad 1) or aromatic (Triad 2) linker showed symmetry breaking charge separation (SB-CS). • SB-CS phenomenon is studied using photoluminescence, time resolved fluorescence, transient absorption spectroscopy techniques. • The organic solar cell fabricated using Triad 2 resulted in better device performance compared to Triad 1 due to increased open circuit voltage (V oc) because of more effective SB-CS state. • Triad 2 shows overall better power conversion efficiency of 4.4 % with FF 67 % in comparison to Triad 1. Multichromophoric D-A-D triads synthesized using perylenediimde (PDI) bonded with naphthalenediimide (NDI) units via aliphatic (Triad 1) or aromatic (Triad 2) linker is studied for symmetry breaking charge separation (SB-CS) by selective excitation of the NDI/PDI chromophores. NDI chromophore on excitation transfers electron to PDI chromophore and type of linker played crucial role in stability of generated CS state. Photoluminescence, time resolved fluorescense and transient absorption spectroscopy tools have been used to study the phenomenon. The optical as well as electrochemical study confirmed intramolecular electron transfer from NDI to PDI chromophore. Stable SB-CS state formation is directly resulted in increased open circuit voltage (V oc) of Triad 2 based organic solar cell devices. The selective excitation of chromophoric center and SB-CS in D-A-D type triad is the demand of present electronic device for the formation of long lived charge carrier. [ABSTRACT FROM AUTHOR]

Previous studies have shown influence of aliphatic side chain length and type on the transport properties of naphthalenediimide (NDI) materials by affecting molecular arrangement. There is lack of comparative study on the presence or absence of unsaturation in side chain and its effect on optical and electronic properties of NDI. The present work focuses on the structure–property relationship of four NDI derivatives bearing octyl (C8, OctA-NDI), hexadecyl (C16, HD-NDI), octadecyl (C18, ODA-NDI) and oleyl (C18-un, unsaturated, OLA-NDI) chain on imide-nitrogen. The self-assembling behaviour of the molecules is studied in concentrated solutions as fresh and aged samples in four different solvents by absorbance and emission spectroscopy. With increase in alkyl chain length, the aggregation behaviour is observed to increase. Very interestingly introduction of unsaturation in side chain reduces aggregation and restores the monomeric properties. Self-assembled microstructures formation was studied by scanning electron microscopy where all the four materials show different types of self-assembly formation. Finally, we compared the thermally activated electron conductivity and electron mobility of NDI derivatives, where also the side chain structure clearly influences the electron transport. Electron mobility decreases on increasing chain length from C8 to C18 and again increases in C18-un. A rationale for the structure–property relationship has been given based on the molecular packing and intermolecular π–π interactions. This study contributes significantly towards designing new NDI derivatives bearing long side chains with hampered aggregation for niche applications. [ABSTRACT FROM AUTHOR]