Rigid oligomers based on the combination of 3,6-dimethoxythieno[3,2-b]thiophene and 3,4-ethylenedioxythiophene

Multifunctional Heteropentalenes: From Synthesis to Optoelectronic Applications

In the broad family of heteropentalenes, the combination of two five-membered heterocyclic rings fused in the [3,2-b] mode has attracted the most significant attention. The relatively straightforward access to these structures, being a consequence of the advances in the last two decades, combined with their physicochemical properties which match the requirements associated with many applications has led to an explosion of applied research. In this Perspective, we will discuss the recent progress of heteropentalenes' usefulness as an active element of organic light-emitting diodes and organic field-effect transistors. Among the myriad of possible combinations for the different heteroatoms, thieno[3,2-b]thiophenes and 1,4-dihydropyrrolo[3,2-b]pyrroles are subject to the most intense studies. Together they comprise a potent optoelectronics tool resulting from the combination of appreciable photophysical properties, chemical reactivity, and straightforward synthesis.

Bis-EDOT end capped by n-hexyl or n-hexylsulfanyl groups: the effect of the substituents on the stability of the oxidized states

Sulfur atoms of hexylsulfanyl groups stabilize the radical cation and dication states and prevent the σ-dimerization of the radical cation.

Long-chain 3,4-ethylenedioxythiophene/thiophene oligomers and semiconducting thin films prepared by their electropolymerization

A series of soluble H-terminated conjugated oligomers incorporating 3,4-ethylenedioxythiophene (EDOT) combined with a small number of thiophene units and ranging in length from four to eight EDOT/thiophene groups was prepared with the ultimate goal to investigate if facile formation of a reactive trication radical species would enable electrochemical polymerization of such long-chain oligomers. Spectroscopic and electrochemical studies of the oligomers revealed some general dependencies of their electronic properties on the total number and position of EDOT groups. It was the number of consecutive EDOT units rather than total number of these units which was found to have the most profound effect on electronic energy gap and conjugation length. This influence originates from the especially strong planarization induced in the conjugated backbone by the incorporation of EDOT units. In contrast, incorporation of thiophene units was found to result in loss of the conformational stabilization. This phenomenon was analyzed using the natural bond orbital computational approach, which revealed the predominantly hyperconjugative nature of the EDOT-induced conformational stabilization. Whereas shorter oligomers, in agreement with the general consensus, were found to be inert toward electrochemical polymerization due to low reactivity of electrochemically generated cation radical and dication species, the longest oligomer showed an unprecedentedly efficient electropolymerization to yield a stable thin film of an electroactive polymer. The efficient electropolymerization of the long-chain oligomer was found to be in agreement with the formation of a reactive trication radical species. The electronic and spectral properties of the resulting semiconducting polymer film were studied by various electrochemical and spectroelectrochemical methods, as well as conductive probe AFM technique, and revealed a number of unusual features (such as electrical rectifying switching behavior) consistent with the possibility of increased molecular order in this material.