Mechanochemical synthesis of diimide based electron acceptors for organic photovoltaics applications

It has been predicted that solar energy will play a key role in solving the serious environmental problems that face our planet. The pursuit of clean, renewable, cost-effective, and high-performance organic photovoltaic (OPV) technologies has attracted considerable efforts from both academia and industry. Some of the most promising materials for OPVs are those based on systems such as naphthalene diimide (NDI), or perylene diimide (PDI). These structures are known to be excellent electron acceptor species for organic electronic applications because of their strong light absorption and chemical stability. However, the efficient synthesis of these compounds is hindered by poor yields and the need for harsh solvent-based conditions, especially for their brominated derivatives. This report details our efforts towards synthesising these high value compounds in a more environmentally friendly way using solvent free mechanochemistry in a ball mill. With these molecules synthesised, our long-term goal is to study their solid-state polymerisation resulting in an environmentally benign synthesis of materials suitable for the next generation of organic solar cells

Solvent-free synthesis of core-functionalised naphthalene diimides by using a vibratory ball mill: Suzuki, Sonogashira and Buchwald–Hartwig reactions

Solvent-free synthesis by using a vibratory ball mill (VBM) offers the chance to access new chemical reactivity, whilst reducing solvent waste and minimising reaction times. Herein, we report the core functionalisation of N,N’-bis(2-ethylhexyl)-2,6-dibromo-1,4,5,8-naphthalenetetracarboxylic acid (Br2-NDI) by using Suzuki, Sonogashira and Buchwald–Hartwig coupling reactions. The products of these reactions are important building blocks in many areas of organic electronics including organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs) and organic photovoltaic cells (OPVCs). The reactions proceed in as little as 1 h, use commercially available palladium sources (frequently Pd(OAc)2) and are tolerant to air and atmospheric moisture. Furthermore, the real-world potential of this green VBM protocol is demonstrated by the double Suzuki coupling of a monobromo(NDI) residue to a bis(thiophene) pinacol ester. The resulting dimeric NDI species has been demonstrated to behave as an electron acceptor in functioning OPVCs

Solvent-free synthesis of core-functionalised naphthalene diimides by using a Vibratory Ball Mill: Suzuki, Sonogashira and Buchwald–Hartwig reactions

Solvent-free synthesis by using a vibratory ball mill (VBM) offers the chance to access new chemical reactivity, whilst reducing solvent waste and minimising reaction times. Herein, we report the core functionalisation of N,N’-bis(2-ethylhexyl)-2,6-dibromo-1,4,5,8-naphthalenetetracarboxylic acid (Br2-NDI) by using Suzuki, Sonogashira and Buchwald–Hartwig coupling reactions. The products of these reactions are important building blocks in many areas of organic electronics including organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs) and organic photovoltaic cells (OPVCs). The reactions proceed in as little as 1 h, use commercially available palladium sources (frequently Pd(OAc)2) and are tolerant to air and atmospheric moisture. Furthermore, the real-world potential of this green VBM protocol is demonstrated by the double Suzuki coupling of a monobromo(NDI) residue to a bis(thiophene) pinacol ester. The resulting dimeric NDI species has been demonstrated to behave as an electron acceptor in functioning OPVCs.</p