Enhanced Hole Carrier Transport Due to Increased Intermolecular Contacts in Small Molecule Based Field Effect Transistors

Abstract

Small molecules and oligomers can be synthesized with very high purity and precise molecular weights, but they often do not form uniform thin films while processed from solution. Decreased intermolecular contacts between the small molecules are another disadvantage. To increase the intermolecular contacts in small molecules, we have chosen i-indigo, as one of the conjugated molecular units. The electron poor i-indigo has been connected with electron rich triphenylamine to synthesize a donor-acceptor-donor type small molecule. The propeller shaped triphenylamine helps to increase the solubility of the small molecule as well as isotropic charge transport. The intermolecular spacing between the molecules has been found to be low and did not vary as a function of thermal annealing. This implies that the intermolecular contacts between the small molecules are enhanced, and they do not vary as a function of thermal annealing. Organic field effect transistors (OFET) fabricated using a small molecule exhibited a hole carrier mobility (μ) of 0.3 cm(2)/(V s) before thermal annealing. A marginal increase in μ was observed upon thermal annealing at 150 °C, which has been attributed to changes in thin film morphology. The morphology of the thin films plays an important role in charge transport in addition to the intermolecular spacing that can be modulated with a judicious choice of the conjugated molecular unit.

Approach to modulate the sensing range of molecular transducers

“…D-iInd was synthesized by carrying out a condensation reaction between 6-bromooxindole and 6-bromoisatin with 96% yield [53]. The structure of the D-iInd was confirmed by 1 H NMR, IR spectroscopy and single crystal X-ray diffraction experiments.…”

“…We have identified commercially available 6-bromoisatin (BI) (Chart 1), which has been recently explored for the synthesis of organic semiconductors, as the transducer [52][53][54]. It must be noted that the BI is extracted from plants, mollusc and fungi and used as anticancer drug as well [55].…”

“…To test this hypothesis, dibromoisoindigo (D-iInd) (Chart 1) was synthesized. The synthesis involves the condensation of BI and BOI in presence of acid [53]. The product, D-iInd, is purified by washing without use of column chromatography.…”

Synthesis of amphiphilic isoindigo co‐polymers for organic field effect transistors: A comparative study

“…In particular, two main factors can alter the intermolecular interaction in the CPs. The first one is the conjugated backbone of the CPs and the second one is the engineering of the side chains of the CPs …”

Donor–acceptor–donor conjugated oligomers based on isoindigo and anthra[1,2-b]thieno[2,3-d]thiophene for organic thin-film transistors: the effect of the alkyl side chain length on semiconducting properties

“…However, although many D-A conjugated oligomers have been synthesized and characterized, [41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57] few of them exhibited charge carrier mobility higher than 0.1 cm 2 V -1 s -1 . [53][54][55][56][57] Introduction of polyaromatic units into conjugated framework can enhance the intermolecular interaction due to their rigid and planar chemical structures, and is believed to be able to improve charge transport properties of organic semiconductors. 58 It is rational that D-A conjugated oligomers constructed with polyaromatics may have promising semiconducting properties.…”