Polymorphism in Crystalline Microfibers of Achiral Octithiophene: The Effect on Charge Transport,Supramolecular Chirality and Optical Properties |
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| Authors: | Francesca Di Maria Eduardo Fabiano Denis Gentili Mariano Biasiucci Tommaso Salzillo Giacomo Bergamini Massimo Gazzano Alberto Zanelli Aldo Brillante Massimiliano Cavallini Fabio Della Sala Giuseppe Gigli Giovanna Barbarella |
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| Affiliation: | 1. ISOF, MIST.E‐R, Mediteknology, Consiglio Nazionale Ricerche, Via P. Gobetti 101, Bologna, Italy;2. NNL CNR‐Istituto Nanoscienze, Via Arnesano, Lecce, Italy;3. ISMN, Consiglio Nazionale Ricerche, Via P. Gobetti 101, Bologna, Italy;4. NNL‐CNR Nanoscience Institute, c/o Dpt, Fisica Ed. G. Marconi, Center for Life, NanoScience, La Sapienza University and IIT, Viale Regina Elena 295, Roma, Italy;5. Dpt of Industrial Chemistry Toso Montanari, University of Bologna, Viale Risorgimento 4, Bologna, Italy;6. Dpt of Chemistry Giacomo Ciamician, University of Bologna, Via Selmi 2, Bologna, Italy;7. Dpt Ingegneria Innovazione, Università del Salento, Via Arnesano, Lecce, Italy |
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| Abstract: | Polymorphic crystalline microfibers from an achiral octithiophene with one S‐hexyl substituent per ring are separately and reproducibly grown with the same characteristics on various solid surfaces, including the interdigitated electrodes/SiO2 surface of a bottomcontact field‐effect transistor. The arrangement of the same molecule in two diverse supramolecular structures leads to markedly different electronic, optical, and charge mobility properties. The microfibers—straight and yellow emitting or helical and red emitting—exhibit p‐type charge transport characteristics, with the yellow ones showing a charge mobility and on/off current ratio of one and three orders of magnitude, respectively, greater than the red ones. Both forms show circular dichroism signals with significant differences from one form to the other. DFT calculations show that the octithiophene exists in two different quasi‐equienergetic conformations aggregating with diverse orientations of the substituents. This result suggests that the observed polymorphism is conformational in nature. The self‐assembly, driven by sulfur–sulfur non‐bonding interactions, amplifies the small property differences between conformers, leading to quite different bulk properties. |
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| Keywords: | supramolecular materials hierarchical structures fibers conjugated polymers electro‐optical materials polymorphism |
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