Carbonyl-Terminated Quinoidal Oligothiophenes as p-Type Organic Semiconductors

Abstract

<jats:p>A series of quinoidal oligothiophenes terminated with carbonyl groups (nTDs, n = 2–4) are studied as p-type organic semiconductors for the active materials in organic field-effect transistors (OFETs) both by the theoretical and experimental approaches. The theoretical calculations clearly show their high-lying highest occupied molecular orbital (HOMO) energy levels (EHOMOs), small reorganization energies for hole transport (λholes), and large contribution of sulfur atoms to HOMOs, all of which are desirable for p-type organic semiconductors. Thus, we synthesized nTDs from the corresponding aromatic oligothiophene precursors and then evaluated their physicochemical properties and structural properties. These experimental evaluations of nTDs nicely proved the theoretical predictions, and the largest 4TDs in the series (4,4′′′-dihexyl- and 3′,4,4″,4′′′-tetrahexyl-5H,5′′′H-[2,2′:5′,2″:5″,2′′′-quaterthiophene]-5,5′′′-dione) can afford solution-processed OFETs showing unipolar p-type behaviors and hole mobility as high as 0.026 cm2 V−1 s−1.</jats:p>

Quinoidal Small Molecule Containing Ring-Extended Termini for Organic Field-Effect Transistors

“…To establish a quinoidal structure, electron-withdrawing groups (EWGs) should be used at termini. A few EWGs are used for the terminal groups of quinoidal molecules such as dicyanomethylene (DCM), quinone, carbonyl, and para -quinodimethane, as shown in Figure . − The DCM group is generally used for quinoidal oligothiophenes with high performance in OFET devices. − However, the DCM-terminated quinoidal molecules require rather complex procedures, including the preparation of dibrominated aromatic compounds, Pd-catalyzed Takahashi coupling reaction, and oxidation of bis­(dicyanomethyl)-precursors by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone. , …”

Quinoid‐Aromatic Resonance for Very Small Optical Energy Gaps in Small‐Molecule Organic Semiconductors: A Naphthodithiophenedione‐oligothiophene Triad System

“…These results might indicate that the rod-shaped molecules would form a π-/ alkyl-segregated lamellar structure on the substrates with some tilt, bent, and/or alkyl-alkyl interdigitation as observed in related molecules. [47] In the structures, the strong inter-backbone interaction of Q4T and Q6T would be the driving force for strong inter-core interaction in the in-plane direction that gives rise to decent hole and electron mobilities higher than 10 À 2 cm 2 V À 1 s À 1 .…”

Synthesis and characterization of naphthalenediimide-thienothiophene-conjugated polymers for OFET and OPT applications

“…[14][15][16] Polymeric and small semiconductor organic materials, which are the key components of OFET devices, may have p-type (hole dominant), n-type (electron dominant) or ambipolar (both carriers) properties. [17][18][19] In contrast to p-type semiconductors, the advancement of n-type devices has been limited because of their poor stability and low electron mobility. To overcome this issue, achieving a deep-lying lowest unoccupied molecular orbital (LUMO) energy level is one of the effective approaches.…”