Synthesis and electron-transport properties of N-trifluoromethylphenyl-phthalimides containing selenophene substituents

Abstract

Trifluoromethylphenyl substituted phthalimides (PIs) containing oligoselenophene and phenylselenophene substituents were synthesized. Spectroscopic studies show that increasing the number of selenophene units causes the UV-Vis and photoluminescence maxima of the selenophene substituted PIs to shift to longer wavelengths. Analysis of the single crystal structure shows that the biselenophene substituted derivative has a layered structure, no center of symmetry and a molecular network with close contacts between Se atoms. XRD patterns of the PI derivatives indicate they have similar layered structures. These substances were used to fabricate field-effect transistors (FET)s by using the vapor deposition method. The FET derived using the biselenophene substituted PI exhibits clear n-type characteristics with an electron mobility of ca. 10⁻⁴ cm² V⁻¹ s⁻¹. The FET prepared using the more highly conjugated terselenophene derivative also displays n-type FET characteristics with a slightly higher threshold voltage. Moreover, n-type behavior is also displayed by a highly crystalline thin film generated from the phenylselenophene derivative. The LED light responsiveness of FET characteristics was investigated. While the FET formed from the terselenophene derivative maintains a saturation drain–source current (I_DS) operation along with a three-fold increase of electron mobility upon irradiation, those derived from the biselenophene and phenylselenophene derivatives display Ohm's law-like I_DS. The difference in light responses are discussed in terms of conductivity differences.