Thiophene-Fused Naphthalene Diimides: New Building Blocks for Electron Deficient π-Functional Materials

Abstract

Development of novel π-conjugated building blocks that can be integrated into molecular or macromolecular systems is key to the evolution of new superior organic semiconductors utilized as the active materials in organic electronics devices such as organic field-effect transistors (OFETs), organic photovoltaics (OPVs), and organic thermoelectric (TE) devices. This review affords a brief overview of thiophene-fused naphthalene diimide (NDI), namely naphtho[2,3-b:6,7-b¤]dithiophene diimide (NDTI) and naphtho [2,3-b]thiophene diimide (NTI), recently developed as novel electron deficient building blocks for n-type and ambipolar organic semiconductors. These thiophene-fused NDI building blocks had not been known until 2013 owing to their synthetic difficulty; more precisely, the difficulty in attaching fused-thiophene ring(s) on the NDI core. We have successfully established a thiophene-annulation reaction on ethyne-substituted NDI derivatives, which allows us to elaborate various NDTI and NTI derivatives. The key features of these building blocks are low-lying energy levels of lowest unoccupied molecular orbitals (LUMO, 3.84.1 eV below the vacuum level) and easy functionalizability of the thiophene ¡-positions, which allows their derivatives and polymers to conjugate efficiently with additional π-and comonomer units. These features make the NDTI-and NTIderivatives and polymers promising n-type and ambipolar materials for OFETs and acceptors for OPVs. In fact, various useful materials have already been derived from the NDTI and NTI building blocks: air-stable n-type small molecules and polymers with high electron mobility (³0.8 cm 2 V ¹1 s ¹1), ambipolar oligomers and polymers with well-balanced hole and electron mobilities, doped n-type semiconductors affording bulk conductors applicable to n-type TE materials, and electron acceptor molecules and polymers for OPVs showing promising power conversion efficiencies of up to 9%. These impressive and diversified device performances testify the usefulness of thiophene-fused NDI building blocks in the development of new electron deficient π-functional materials.

Recent Advances in the Core‐Annulation of Naphthalene Diimides

“…Stille, or copper iodide‐assisted Stille coupling polymerizations of 33 or 2,7‐bis(trimethylstannyl)‐NDI derivative 35 , produces a series of semiconducting polymers, represented by 36 , based on naphthodithiophene diimides and different co‐monomer units such as vinylene (V), thiophene (T), bithiophene (BT), thieno[3,2‐b]thiophene (TT), thienylenevinylene (TV), dithieno[3,2‐ b :2′,3′‐ d ]thiophene (DTT), naphtho[1,2‐ b :5,6‐ b ′]dithiophene (NDT), benzo[c][1,2,5]thiadiazole (BTz), naphtho[1,2‐ c :5,6‐ c ′]‐bis[1,2,5]thiadiazole (NTz) or benzo[1,2‐ c :4,5‐ c ′]bis[1,2,5]‐thiadiazole (BBT) (Scheme ) . The synthesis of copolymers bearing donor units as co‐monomers ( 36 , π 1 , Scheme ) was achieved with higher yields utilising the dibromo precursor 33 and the respective stannylated co‐monomer units under Stille coupling conditions, whereas copolymers bearing electron‐deficient co‐monomer units ( 36 , π 2 , Scheme ) were synthesized with better yields under a copper iodide‐assisted Stille coupling polymerization.…”

“…Thiophene‐based NDIs are popular as promising n‐type and ambipolar materials for OFETs and acceptors for OPVs in organic electronics, as a result of the low‐lying energy levels of the LUMO (3.8–4.1 eV). Just as important is the ease of functionalisation with conjugated oligomers or polymers, leading to extended systems with reported good coplanarity . An early example of six‐membered NDI annulene was achieved by reacting Br 4 ‐NDI 4 with sodium 1,2‐dicyanoethene‐1,2‐dithiolate to yield the laterally extended NDI 25 (Scheme ).…”

“…Just as importanti st he ease of functionalisation with conjugated oligomers or polymers, leadingt oe x-tendeds ystems with reported good coplanarity. [24] An earlye xample of six-membered NDI annulene was achieved by reacting Br 4 -NDI 4 with sodium 1,2-dicyanoethene-1,2-dithiolate to yield the laterally extended NDI 25 (Scheme6). Oxidation with hydrogen peroxide leads to am ix of the ring-contracted syn-26 and anti-26 isomers.…”

“…[29] Stille, or copper iodide-assisted Stille coupling polymerizations of 33 or 2,7-bis(trimethylstannyl)-NDI derivative 35, produces as eries of semiconducting polymers, represented by 6). [24,30,31] The synthesis of copolymers bearingd onor units as co-monomers( 36, p 1 , Scheme 6) was achieved with highery ields utilising the dibromo precursor 33 and the respective stannylated co-monomer units under Stille coupling conditions, whereas copolymers bearing electron-deficient co-monomer units (36, p 2 , Scheme6)w ere synthesized with better yields under ac opper iodide-assisted Stille coupling polymerization.…”

De novo Design of Organic Photocatalysts: Bithiophene Derivatives for the Visible‐light Induced C−H Functionalization of Heteroarenes

“…[6] In this light, the development of novel classes of organic photoredox catalysts with good redox properties, and largely available or easily prepared in high yields would contribute to further advance research in photoredox catalysis. [8] However, examples showing their use in the field of photoredox catalysis remain scarce. For example, in organic electronics their semiconductor properties are exploited in organic field-effect transistors (OFETs) and in photovoltaic devices.…”