Synthesis and Optical and Electrochemical Properties of Core-Fluorinated Perylene Bisimides

Abstract

[reaction: see text] A series of bay position difluoro- or tetrafluoro-substituted perylene bisimides have been synthesized by nucleophilic halogen exchange reaction of the corresponding dibromo- and tetrachloro-substituted perylene bisimides, respectively, with potassium fluoride. Compared to the parent unsubstituted perylene bisimides, these compounds display hypsochromically shifted absorption and fluorescence spectra with fluorescence quantum yields up to unity enabling bright yellow emission. Their electrochemical properties and crystal structures of two perylene bisimides are also reported.

Synthetic Routes to Core-fluorinated Perylene Bisimide Dyes and their Properties

“…3. For this derivative, bearing four fluorines at the bay position, the twisting of the perylene core was surprisingly unsymmetrical but, as expected, significantly larger than for difluorinated perylene bisimide dyes [13]. Thus, the dihedral angle of the one bay area is ∼17 • (carbon atoms C16-C4-C3-C22), the other being ∼28…”

“…The absorption and emission maxima of difluorinated derivatives are hypsochromically shifted by 16 and 17 nm, respectively, in comparison with those of the related unsubstituted PBI derivatives. Such hypsochromic shifts are unprecedented for PBI dyes and lead for the first time to a bright yellow fluorescence for this class of fluorophores [13]. The similar absorption coefficients and vibronic progressions in the spectra of difluorinated and unsubstituted perylene bisimides are in agreement with a flat, rather than a twisted, perylene core as has been demonstrated by single crystal X-ray analysis of a difluorinated PBI derivative [13].…”

“…This reaction was carried out in sulfolane with potassium fluoride and catalytic amounts of 18-crown-6, and indeed significantly higher yields (between 25 % and 60 %, see Table 1) were achieved. Notably, the use of the N,N-dimethylimidazolidino-tetramethylguanidinium chloride (CNC + ) catalyst, which was previously applied for Halex reactions [18], was less successful for the fluorination of dibrominated PBIs [13].…”

“…We have presented the crystal structure of the tetrafluorinated PBI 5a in our recently published letter [13]. However, the highly interesting packing properties of this PBI in the solid state that are related to the conformational chirality of core-substituted PBIs, imparted by a dihedral twist of the perylene core [22], were not discussed there.…”

“…As the incorporation of electron-withdrawing, in particular, fluorine groups afforded significant improvements of the n-type semiconducting properties for several classes of organic semiconductors [8a, 12], we have recently introduced the first examples of corefluorinated perylene bisimides [13], and demonstrated very recently that such fluorinated PBIs indeed afford air-stable n-channel semiconductors [14]. Thus, core-fluorinated PBIs are highly promising for OFETs, and hence further derivatives with varied imide sub- stituents are in demand.…”