n‐Type Quinoidal Oligothiophene‐Based Semiconductors for Thin‐Film Transistors and Thermoelectrics

Abstract

Organic electronic devices have gained immense popularity in the last 30 years owing to their increasing performance. Organic thin‐film transistors (OTFTs) are one of the basic organic electronic devices with potential industrial applications. Another class of devices called organic thermoelectric (OTE) materials can directly transform waste heat into usable electrical power without causing any pollution. p‐Type transistors outperform n‐type transistors because the latter requires a lower orbital energy level for efficient electron injection and stable electron transport under ambient conditions. Aromatic building blocks can be utilized in constructing n‐type semiconductors. Quinoidal compounds are another promising platform for optoelectronic applications because of their unique properties. Since their discovery in 1970s, quinoidal oligothiophene‐based n‐type semiconductors have drawn considerable attention as candidates for high‐performance n‐type semiconductors in OTFTs and OTEs. Herein, the development history of quinoidal oligothiophene‐based semiconductors is summarized, with a focus on the molecular design and the influence of structural modification on molecular packing and thus the device performance of the corresponding quinoidal oligothiophene‐based semiconductors. Insights on the potential of quinoidal oligothiophenes for high‐performance n‐type OTFTs and OTEs are also provided.

Stable Quadruple Helical Tetraradicaloid with Thermally Induced Intramolecular Magnetic Switching

“…Quinoidal-conjugated compounds have attracted considerable interest in the context of research on singlet diradicaloids and polyradicaloids, and research on these compounds has elucidated a wealth of electronic characteristics promisingly applicable in organic electronics. [1][2][3][4] Motivated by these findings, incorporation of quinoidal substructures into an π-system has evolved as an important strategy toward molecules containing weakly paired or unpaired π-electrons. [5][6][7] This quinoidal strategy represents a simple approach for tuning a typical molecule with a closed-shell structure to an open-shell radicaloid, exemplified in indenofluorenes, [8][9][10][11] bisphenalenyls, 12,13 zethrenes, [14][15][16][17][18] quinoidal rylenes, [19][20][21][22] conjugated macrocycles, [23][24][25][26][27][28][29][30] and other motifs.…”

“…40 Such changes are referred to evolved electronic structures, and accordingly imparts particularly interesting optoelectronic and magnetic properties for organic materials. [1][2][3][4][5][6][7] For an irreversible open-shell radicaloid based on the quinoidal structure, its conjugated length [19][20][21][22] and topology [41][42][43][44][45][46][47][48] play a significant role in determining electronic parameters such as the diradical character index (y 0 ) and the singlet-to-triplet energy gap (ΔE S-T ), which are closely associated with observable magnetic properties. Previously reported radicaloid examples have revealed approaches to rational modulation of parameters, that is, tunable y and ΔE S-T values, 49 which are nevertheless relied on for the structural alteration of either quinoidal cores [5][6][7] or conjugated modes.…”

“…The large π-core PQ contains 24 sp 2 -hybridized π-electrons with a fully quinoidal character, which has been rarely explored in reported π-systems, probably due to its high reactivity. In this regard, bulky aryl groups are attached to kinetically block the most reactive sites, and they also result in a rigid [4]helicene structure at two cove-regions. In addition, the existence of four alkoxy groups at the two bay-regions further leads to an ultimately quadruple helical structure in the resulting TBCP.…”

High-yield and sustainable synthesis of quinoidal compounds assisted by keto–enol tautomerism

“… 1–7 In particular, the low-lying lowest unoccupied molecular orbital energy levels of these compounds make them ideal n-type semiconductors, which are crucial for the development of organic logic circuits and organic thermoelectrics. 4,8 In addition, they can be used as magnetic semiconductors for organic spintronics 5 and as singlet fission materials for photovoltaic devices due to their diradical character. 9–11 …”

N‐Sulphonatoalkyl indophenine derivatives: Design, synthesis and dyeing properties on wool, silk and nylon fabrics

“…Recently, quinonoidal heterocycles have emerged as promising functional dyestuffs in the fields of organic field‐effect transistors (OFETs), 14 organic photovoltaics (OPV), 15 and dye‐sensitised solar cells (DSCs) 16 . Their unique features include 17–21 deep tinctorial colours despite limited π‐conjugation systems, insensitive to oxygen and water ascribed to low HOMO (highest occupied molecular orbital)/LUMO (lowest unoccupied molecular orbital) energy levels, high molecular planarity, and rigid backbone structures. Quinonoidal heterocyclic structures can also be considered as potential chromophores for the design of textile dyestuffs.…”