Boosting the Charge Transport Property of Indeno[1,2‐b]fluorene‐6,12‐dione though Incorporation of Sulfur‐ or Nitrogen‐Linked Side Chains

Abstract

Alkyl chains are basic units in the design of organic semiconductors for purposes of enhancing solubility, tuning electronic energy levels, and tailoring molecular packing. This work demonstrates that the carrier mobilities of indeno[1,2-b]fluorene-6,12-dione (IFD)-based semiconductors can be dramatically enhanced by the incorporation of sulfur-or nitrogen-linked side chains. Three IFD derivatives possessing butyl, butylthio, and dibutylamino substituents are synthesized, and their organic field-effect transistors (OFET) are fabricated and characterized. The IFD possessing butyl substituents exhibits a very poor charge transport property with mobility lower than 10 −7 cm 2 V −1 s −1 . In contrast, the hole mobility is dramatically increased to 1.03 cm 2 V −1 s −1 by replacing the butyl units with dibutylamino groups (DBA-IFD), while the butylthio-modified IFD (BT-IFD) derivative exhibits a high and balanced ambipolar charge transport property with the maximum hole and electron mobilities up to 0.71 and 0.65 cm 2 V −1 s −1 , respectively. Moreover, the complementary metal-oxide-semiconductor-like inverters incorporated with the ambipolar OFETs shows sharp inversions with a maximum gain value up to 173. This work reveals that modification of the aromatic core with heteroatom-linked side chains, such as alkylthio or dialkylamino, can be an efficient strategy for the design of high-performance organic semiconductors.

Theoretical study of charge-transport and optical properties of indeno[1,2-b]fluorene-6,12-dione-based semiconducting materials

“…It can be clearly seen that the first bright-state transition for B-IFD, BT-IFD and DBA-IFD corresponds to S 0 ! S 1 from the HOMO orbital to LUMO orbital, which is consistent with experimental data (Fan et al, 2017). Further, the second bright state transition of these three structures corresponds with the S 0 !…”

“…The ranges of mobility values of BT-IFD estimated in the same layer are summarized in Table 3. We can see that the ranges of the hole and the electron mobility values in the BT-IFD crystal agree well with the experimental measurements reported by Fan et al (2017), which verifies the rationality of our computation method and strategy. Comparison of the predicted hole-and electron mobility values for BT-IFD indicates that the holes in BT-IFD are intrinsically more mobile than the electrons in BT-IFD.…”

“…The maximum electron-transfer mobility value is about 0.44 cm 2 s À1 V À1 , while the maximum hole-transfer mobility value is only 0.01 cm 2 s À1 V À1 , which is lower than the reported hole transport mobility (0.19 cm 2 s À1 V À1 ). Considering that the microstructural characteristics of the dielectric layers in thin-film OFETs and the temperature of semiconductor film deposition strongly influence the semiconductor film-growth mode and phase selection (Kim et al, 2007;Fan et al, 2017), our calculated hole-transfer mobility values, based on X-ray crystal structures, can be regarded as a reference. From our predicted mobility values of DBA-IFD, we find that the optimum electron transfer mobility is about 44 times higher than the optimum hole transfer mobility, suggesting that DBA-IFD and their derivatives should have good prospects as n-type OFET materials rather than p-type semiconducting materials.…”

“…Ozdemir et al (2016) synthesized a series of indeno[1,2b]fluorene-6,12-dione/thiophene derivatives with hydrocarbon substituents atand !-positions as side groups, and they demonstrated that rational repositioning of the -substituents to molecular termini greatly benefits the -core planarity and results in favourable structural and optoelectronic characteristics for more efficient charge transport in the solid state. Fan et al (2017) designed IFD-based molecules modified with different side chains, and investigated the impact of different heteroatom linkage in the side chains on their OFET performance. Their work revealed that the carrier mobilities of a classic organic semiconductor IFD could be boosted by several orders of magnitude by replacing the butyl chains with butylthio or dibutylamino substituents.…”

N-Cyanoimine as an electron-withdrawing functional group for organic semiconductors: example of dihydroindacenodithiophene positional isomers

“…In the IF-dione series, the disubstitution of the side phenyl rings of 1,2-b-IF(=O) 2 has widely been studied whereas it is almost absent for its regioisomer 2,1-b-IF(=O) 2 . 23,37,[47][48][49][50] Alkyl chains, 51 amines, 51 halogen atoms 32,52 or substituted thiophenes 53 57 ) have also been described, leading in some cases to highly efficient materials with low LUMO energy level and high µ FE such as in 1,2-b-IF(F 6 )(=O) 2 (LUMO= -3.53 eV, µ E = 0.16 cm² V -1 s -1 ). 32 Similarly, para-IDT(=O) 2 58, 59 (framed in green chart 2) or from its isomer meta-IDT(=O) 2 , (which synthesis has not been reported so far) have followed similar design strategies.…”