In this paper, Tetraphenyldipyranylidene (DPPh), a large quinoidal
planar π-conjugated heterocyclic, was considered as primary organic
molecule in organic field effect transistors (OFETs).
Electron-withdrawing atoms such as F, Cl, and Br were attached to the
H-atoms of four peripheral phenyl groups of para-positions relative to
the O-atoms of DPPh. Density functional theory (DFT) calculations at the
M06-2X/6-311G++ (d,p) level were performed. The influences of the
different electron-withdrawing atoms such as F, Cl, and Br on the
electronic and optical properties, charge transport parameters, and
charge carrier mobility were investigated. The absorption and emission
spectra of the DPPh and its derivatives were theoretically simulated in
OFETs. The simulated spectra show an intense peak in the visible region
(400-650 nm), in which the highest adsorption/emission intensity is
related to DPPh-Br. Moreover, the charge injection energy barrier of
DPPh and its derivatives were calculated by considering Pt as the source
electrode. Based on the results, a greater hole transport is predicted
than the electron transport. Moreover, the obtained ratio of the
hole/electron mobility and the theoretical correlations between the
charge transport parameters of monomers and dimers show that the
insertion of the electron-withdrawing atoms in the DPPh structure is a
promising strategy to have an ambipolar or n-type semiconductor, too.
The obtained results show that introducing electron-withdrawing atoms at
the para-position of the DPPh improves the hole/electron injection and
transport process in the OFET devices. Finally, DPPh-Br shows a great
performance in comparison with the substituted F and Cl atoms in the
OFETs devices.
A Gated Four Probe Technique for Field Effect Measurements on Disordered Organic Semiconductors