TETRA-FUN · Synthesis of innovative organic semiconductors based on functionalized tetracenes and derivatives of rubrene

Synthesis of innovative organic semiconductors based on functionalized tetracenes and derivatives of rubrene

Project aims and objectives The objective of this project was the synthesis of new derivatives of tetracene, homologous of rubrene and the study of their optical and electronic properties, both at molecular and crystal level. More into the details, the main objectives of the project were the synthesis of new organic semiconductors, belonging to the family of aryl-tetracenes (the same of rubrene), the growth of good quality single crystals and of crystalline thin films (by sublimation in vacuum or by solution methods) and the analysis of charge transport properties of these new materials. Through the comparison between the properties of these compounds with those of rubrene and tetracene, we wanted to learn about the effect of different substituents on supramolecular structure and solid state properties. The main goal was to analyse into the details the synthesis and the reactivity of aryl-tetracenes, homologues of rubrene, and to prepare new organic semiconductors with high mobility, similar or better to that shown by rubrene single crystals and without its limitations. A second goal was to find a way to overcome the limitations that hinder the use of those compounds into real devices, namely the low stability towards oxidation and the lack of solution-based techniques to prepare crystalline semiconductors. The expected impact of these activities is in the field of materials for organic electronics. The results obtained so far and the results of the activities that are in progress at the end of the progress provided an improvement of the knowledge in the field of the chemistry of acene-based organic semiconductors and on their application in materials science. The results expected from the activities that are still in progress should provide further advance into the comprehension of basic physics phenomena occurring in organic semiconductor, namely the origin of the high charge mobility observed into rubrene. More into the details, the most interesting outcomes of this project were: 1) the preparation of a library of compounds belonging to the class of tetraaryltetracenes. One of most interesting results, from the synthetic point of view, was the complete elucidation of the reaction mechanism responsible for the synthesis of rubrene. We were able to show that the current, commonly accepted mechanism was incomplete and unable to predict the formation of a concurrent compound (cyclobutene) and on the basis of our data, we proposed a more complete mechanism. We think that this result will be very useful for the community of chemists working on acenes and organic semiconductors. 2) the growth of single crystals and determination of their crystal structure. Among the compound prepared during the project, we found an interesting derivative crystallises with the same packing motif as rubrene and shows and enhanced stability towards photooxidation. 3) preparation of thin film by different techniques (solution and evaporation under vacuum). 4) analysis of electrical parameters of organic field effect transistor (OTFTs) (in progress). The analysis of the electrical characteristics of selected compounds, which crystallises with the same packing motif as rubrene and with an increased stability are in progress. The results on the increased stability of new derivatives of rubrene, together with the electrical measurement in progress on single crystals, should clarify the origin of the high mobility observed into rubrene.

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