Organic semiconductor design for light-emitting electrochemical cell technology

Abstract

Organic light-emitting electrochemical cells (OLECs) that comprise an active layer, an optional hole-injection layer, and a pair of electrodes, are promising alternatives to currently prevalent technologies. Small-molecule OLECs with active layers based on functionalised fluorene fragments tethered, by hydrocarbon chains, to alkylimidazolium pendants have a number of properties that make them especially viable targets in the design of next-generation OLEC devices. Fluorene’s ease of functionalisation allows a systematically varied group of arylfluorene salts to be generated, and a structure-activity relationship to be investigated. Cross- coupling of alkylated bromofluorenes with substituted bromobenzenes, by way of the corresponding dioxaborolanes, gives a set of neutral smart ink precursors that can be quaternised with alkylimidazoles. Inductive (both +I and -I) and mesomeric effects (both +M and -M) at the 3 and 4 positions of the aryl substituents are examined. Head-to-head comparison of matched pairs reveals the effects of substituent type and substitution pattern. 2,7-diarylfluorene smart inks and their 2-arylfluorene cousins are compared in order to establish the effect of, and extent of the π-system, independently of aryl group substitution pattern. The practical viability of smart inks bearing methylim- idazolium pendants is compared with those bearing octylimidazolium pendants. These arylfluorene smart inks form the training set used to establish an efficient, pre- dictive computational modelling procedure. The substrate scope is probed by computa- tional and spectroscopic analysis of a group of polyarenes based on phenanthrene, and the generation of a functioning OLEC device from a smart ink in this chemical family is demonstrated. The predictive model, in combination with a genetic algorithm, is used to further extend the substrate scope and generate a UV-emitting arylpyridine and a blue-emitting arylpyridinium analogue.

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Identifiers

ORCID for David Harrowven: orcid.org/0000-0001-6730-3573

ORCID for Richard Whitby: orcid.org/0000-0002-9891-5502

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