Re po rt s 20 17 16 Synthesis of Core Substituted Napthalenediimides for n - Type Organic Semiconducting

The lack of stable high performance organic n-type semiconductors is a major challenge for the field. We explored one possibility for creating such a material by further augmenting previously successful N,N’-bis(cyclohexyl) napthalenediimide with a novel core extension. The synthesized monoand biscore-extended bis(cyclohexyl) napthalenediimides were given to a collaborating group to measure the compound’s electronic properties. Introduction: Effective organic semiconductors are highly desirable in industry because organics, unlike silicon, are generally elastic and can be deposited with relatively simple solution chemistry techniques, thus allowing for flexible electronics devices and inexpensive roll to roll manufacturing. Semiconductor performance for thin film, field effect transistors is quantified through field effect mobility (FET), which is defined as the average charge carrier (hole or electron) drift velocity per unit electric field. Semiconductors can be considered high performance if they have a FET greater than that of amorphous silicon, which is 1 cm2 V-1 s-1. One of the major challenges in the field of organic semiconductors today is the lack of n-type organic semiconductors that can match the performance of their p-type counterparts [1]. Previous research has demonstrated that the use of cyclohexyl imides dramatically improves the FET of naphthalenetetracarboxylic diimide (NDI), a widely studied and attractive organic n-type semiconductor candidate, to near 6 cm2 V-1 s-1 as compared to 0.16 cm2 V-1 s-1 for its straight chain hexyl counterpart [2], though issues with stability in air still remain [1]. Recently core substitution has emerged as a powerful tool to improve the stability and tune the electronic properties for NDIs [3]. Our lab has had previous success with core expansion using alkynyl groups [4]. Our research goal was to combine these results by synthesizing core-extended cyclohexyl NDIs. Synthesis: The synthetic scheme is outlined in Figure 1. For step one, a mixture of unsubstituted, monobromo-, and dibromo1,4,5,8-naphthalenetetracarboxylic acid anhydride was reacted with cyclohexamine in acetic acid at reflux for one hour. After the reaction, the resultant precipitate was filtered through a Buchner funnel, washed with methanol and left to dry in the vacuum oven overnight. The dry precipitate was separated using silica gel liquid column chromatography with chloroform as the solvent. Fractions for unsubstituted, monobromo-, and dibromocyclohexyl NDI were collected separately. Figure 1: Synthetic scheme for achieving monoand biscore extended bis(cyclohexyl) napthalenediimides. (1) Imide Synthesis. (2) Sonogashira Coupling. (3) Deprotection.