Quinoidal Oligothiophenes with (Acyl)cyanomethylene Termini: Synthesis, Characterization, Properties, and Solution Processed n-Channel Organic Field-Effect Transistors

Abstract

A new class of oligothienoquinoidal derivatives with newly employed (acyl)cyanomethylene termini are reported. For the synthesis of (acyl)cyanomethylene-substituted thienoquinoidals, similar methods successfully employed for the synthesis of related dicyanomethylene-or ((alkyloxy)carbonyl)cyanomethylene-substituted thienoquinoidals were not applicable, and thus a new synthetic route was developed. The introduced (acyl)cyanomethylene terminal groups act both as a solublizing group to facilitate solution processability and an electron-withdrawing group to keep the LUMO energy levels sufficiently low for n-channel organic semiconductors. The LUMO energy levels estimated from their reduction potential are ∼4.2 eV below the vacuum level, which just falls in between those for the corresponding dicyanomethylene-and ((alkyloxy)carbonyl)cyanomethylene-substituted thienoquinoidals. This qualitatively agrees with the electron-withdrawing nature of the terminal groups; the order of the electron withdrawing nature is cyano-> acyl-> (alkyloxy)carbonyl-groups. Spin-coating chloroform solutions of (acyl)cyanomethylene-substituted thienoquinoidals gave homogeneous thin films on the Si/SiO 2 substrates, and the thin films based on the terthienoquinoidal derivatives became highly crystalline upon thermal annealing. The annealed film acted as the active semiconducting channel in the FET devices under ambient conditions, and the electron mobilities extracted from the saturation regime were ∼0.06 cm 2 V -1 s -1 . These n-channel FET characteristics are nearly the same or slightly better than those of the FETs based on the related ((alkyloxy)carbonyl)cyanomethylene-terminated terthienoquinoidal, indicating that the (acyl)cyanomethylene moiety is a useful terminal group on the thienoquinoidals for the development of soluble n-channel organic semiconductors.

Indandione‐Terminated Quinoids: Facile Synthesis by Alkoxide‐Mediated Rearrangement Reaction and Semiconducting Properties

“…No hole injection and transport were observed for the devices of 5 c , 5 e , 5 f , 5 h , 5 i , 5 j , and 5 k although they showed relatively high‐lying HOMO levels (see Figure S21). A similar phenomenon was observed in other quinoidal compounds, and the actual reason for the absence of hole transport is unclear. Representative output and transfer curves for the devices are shown in Figure (see Figures S19 and S20), and their performance parameters are summarized in Table S6.…”

π‐Conjugated Polymers Incorporating a Novel Planar Quinoid Building Block with Extended Delocalization and High Charge Carrier Mobility

“…The synthesized quinoid monomer QuT is afforded as a mixture of isomers, much like other quinoidal molecules . Figure S3 of the Supporting Information shows the theoretically possible isomeric structures of the QuT monomer.…”

Thiophene‐S,S‐dioxidized Indophenine: A Quinoid‐Type Building Block with High Electron Affinity for Constructing n‐Type Polymer Semiconductors with Narrow Band Gaps

“…3b and 3c could be converted into the most-stable 3a by heating at 110 8 8C. An IDTO-containing conjugated polymer, PIDTOTT, was prepared using 3a as ac omonomer through aS tille coupling reaction, and it possesses an arrowb and gap and low energy levels.I no rganic field effect transistors (OFETs), PIDTOTTexhibited unipolar n-type semiconductor characteristics with unexpectedly high electron mobility (up to 0.14 cm 2 V À1 s À1 ), despite its rather disordered chain packing.n-Type organic semiconductors are sought after for use in complementary circuits [1][2][3] and organic solar cells, [4][5][6] but very few n-type semiconductors,p articularly polymers,w ith high carrier-mobility have been reported when compared to reports of p-type semiconductors.Q uinoidal compounds such as TCNQ, [7,8] quinoidal oligothiophenes [9][10][11][12][13][14] and quinoidal fused thiophenes [15][16][17] (Figure 1) have been studied as…”