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SUMMARY:Photochromics meet Organic Electronics: a Novel Generation of Func
 tional Materials and Interfaces - Emanuele Orgiu\, Institut de Science et 
 d'Ingénierie Supramoléculaires (I.S.I.S.)\, Université de Strasbourg\, 
 France
DTSTART:20120124T143000Z
DTEND:20120124T153000Z
UID:TALK35991@talks.cam.ac.uk
CONTACT:Jenny Clark
DESCRIPTION:Photochromic systems are capable of undergoing efficient and r
 eversible photochemical reactions\, i.e.\nto switch between two or more (m
 eta)stable isomers featuring markedly different properties. Such bi- or\nm
 ulti-stable building blocks can then be employed to translate an incoming 
 stimulus such as light into a\nmacroscopic property change of the material
 s.[1]\n\nIn particular\, azobenzenes (AZO) are known to undergo reversible
  photoinduced isomerization\nbetween trans and cis form which can exhibit 
 different optical and electrical properties.\nWe demonstrate that a photoc
 hromic bi-stable AZObenzene-Self-Assembled Monolayer (AZO-SAM)\nchemisorbe
 d on Au electrodes can mediate the injection through the variation of the 
 tunneling barrier\nacross the SAM making it possible to modulate reversibl
 y the charge injection at the Au\nelectrodes/semiconductor interface in an
  organic transistor. The observed result is in full agreement\nwith previo
 us I-V characterizations of the AZO-SAM when incorporated in two terminal 
 junctions as\nstudied by C-AFM[2] and Hg-drop based measurements\,[3] demo
 nstrating that the switching effect of the\ntransport properties relies on
  the difference in tunneling barrier thickness. Wettability properties of 
 the\nAZO-SAM/Au (in its trans and cis isomer) were characterized by contac
 t-angle\, and its work function\nvariation was measured by means of macros
 copic Kelvin Probe.\n\nDiarylethenes (DAEs)[4] are another class of photoc
 hromic systems which are very popular scaffolds in\nmolecular electronics[
 5] because their open and closed isomers feature different HOMO and LUMO\n
 levels depending on the specific irradiation wavelength (UV or white light
 ). Hence other properties such\nas absorption\, emission as well as redox 
 characteristics can be phototuned as well. Promising electrical\ncurrent s
 witching properties achieved by combining DAEs and organic semiconductors 
 in blends were\ntheoretically predicted.[6] The blend between DAE derivati
 ves featuring different energy levels with an\norganic semiconducting poly
 mer such as P3HT was used as a bi-component film forming the\nelectroactiv
 e layer of organic thin-film transistors (OTFTs).Taking into account the h
 ole transport levels\nof P3HT\, we designed and synthesized a DAE molecule
 \, DAE_1\, featuring different ionisation energy\n(IE) in its open and clo
 sed form with respect to the IE of P3HT. To explore the role of different 
 energy\nlevels in the two different DAE isomers with respect to the IE of 
 P3HT we have extended our study to\nDAE_2 with higher IE of both isomers.\
 n\nIn our devices the source-drain current through the channel can be ther
 efore gated both electrically\n(through gate control)\, like in a conventi
 onal OFET\, and optically through photochemical control exerted\neither in
  the charge injection or transport level . Such a proof of concept is inst
 rumental to the field of\norganic electronics which searches for solutions
  to integrate new and more functionalities in a device.\n\nReferences\n[1]
  M.-M. Russew\, S. Hecht\, Adv. Mater. 2010\, 22\, 3348.\n[2] J. M. Mative
 tsky\, G. Pace\, M. Elbing\, M. A. Rampi\, M. Mayor\, P. Samorì\, J. Am. 
 Chem. Soc. 2008\, 130\, 9192.\n[3] V. Ferri\, M. Elbing\, G. Pace\, M. D. 
 Dickey\, M. Zharnikov\, P. Samorì\, M. Mayor\, M. A. Rampi\, Angew. Chem.
 \nInt. Ed. 2008\, 47\, 3407.\n[4] M. Irie\, Chem. Rev. 2000\, 100\, 1683 (
 2000).\n[5] A. J. Kronemeijer et al.\, Adv. Mater. 2008\, 20\, 1467.\n[6] 
 F. L. E. Jakobsson et al.\, J. Phys. Chem. C 2009\, 113\, 18396.
LOCATION:Kapitza Building Seminar Room\, Cavendish Laboratory\, Department
  of Physics
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