Fluorinated organic materials for electronic and optoelectronic applications: the role of the fluorine atom

Abstract

In this article we highlight, by means of selected examples drawn from work performed in our or other laboratories, the features of some classes of fluorinated conjugated materials and their use in electronic devices such as electroluminescent diodes or field effect transistors. A variety of fluorinated conjugated systems, either molecular or polymeric, such as poly(phenylenevinylene)s, poly(phenyleneethynylene)s, polythiophenes, polyphenylenes, are dealt with. Attention is also focused on a different class of electroluminescent compounds, represented by the cyclometalated iridium complexes with various forms (mer and fac). In particular, fluorine atoms lower both the HOMO and LUMO energy levels. Consequently, the electron injection is made easier, the materials display a greater resistance against the degradative oxidation processes and organic n-type or ambipolar semiconducting materials may result. Moreover, the C-H...F interactions play an important role in the solid state supramolecular organization, originating a typical pi-stack arrangement which enhances the charge carrier mobility.

Copper-phthalocyanine based metal–organic interfaces: The effect of fluorination, the substrate, and its symmetry

“…37 Previous work reported the disappearance of the Au(111) herringbone reconstruction under the F 16 CuPc monolayers. 26 However, higher quality STM measurements have now proven the opposite, revealing the substrate reconstruction under the organic overlayer with an fcc/hcp periodicity measured along the [1][2][3][4][5][6][7][8][9][10] direction of 65 ± 3 Å, thus virtually unchanged with respect to the pristine Au(111). While this could be interpreted as the result of very weak molecule-substrate interactions, 31 the reported disappearance of the Au(111) surface state upon F 16 CuPc adsorption, as measured by valence band photoelectron spectroscopy, 26 still supports the picture of a significant interaction.…”

“…31,38 CuPc on Au(111) leads to the growth of crystalline layers characterized by a square unit cell of dimensions a = 13.9 ± 0.7 Å, and it hardly affects the underlying Au(111) surface reconstruction. 30,39 The unit cell vectors are directed along the high symmetry and [1][2][3][4][5][6][7][8][9][10] directions (Fig. 4).…”

“…1). 7,8 As a consequence, perfluorinated copperphthalocyanine (F 16 CuPc, Fig. 1) presents a preferred acceptor behavior and has shown remarkable performance in devices as n-type semiconductor.…”

Synthesis and applications of difluorobenzothiadiazole based conjugated polymers for organic photovoltaics

“…15 Fluorine atoms can lower both the HOMO and LUMO energy levels, so the materials will display a greater resistance against the degradative oxidation. A lower HOMO energy level also means a higher open circuit voltage (V oc ) for polymer solar cells since V oc is usually determined by the difference between the HOMO of the polymer and the LUMO of the fullerene derivative.…”

Donor–acceptor semiconducting polymers for organic solar cells

“…80 The incorporation of the fluorine atom simultaneously lowered the HOMO and LUMO of the D-A polymer, while no effect on the optical bandgap was observed. [92][93][94] The HOMO and LUMO of the polymer 16a were À5.02 and À3.58 eV, whereas that of the polymer 16b were À5.15 and À3.71 eV, respectively. The photovoltaic measurements for the polymer 16b showed a V OC 130 mV higher than that of 16a, which was attributed to the increase in the polymer ionization energy upon fluorine attachment.…”