n-Type Polyimides with 1,3,4-Oxadiazole-Substituted Triphenylamine Units—An Innovative Structural Approach

Abstract

A novel aromatic diamine containing 1,3,4-oxadiazole-substituted triphenylamine (TPA) was successfully synthesized and structurally characterized. Based on this, a series of three aromatic polyimides with high thermal stability were prepared and processed in thin coatings with a grain-like morphology. Their ability to form a dual intramolecular charge transfer complex between TPA and 1,3,4-oxadiazole in the side chain and TPA and phthalimide in the main chain was proven. Both the optical effects and electronic properties were found to be modulated by the competing electron-withdrawing character of 1,3,4-oxadiazole/imide units. The electrochemical investigation suggested their n-type redox capability and electron transporting characteristics, a statement supported by current–voltage measurements of some indium tin oxide/poly­(3,4-ethylenedioxythiophene):polystyrene sulfonate/polyimide/eGaIn prototype devices. Thereby, the present polyimides enable the pathway toward alternative n-type materials currently used in optoelectronics devices.

Synergetic Effect between Structural Manipulation and Physical Properties toward Perspective Electrochromic n-Type Polyimides

“…If the highenergy bands can be accurately assigned to π−π* transitions in the phenylene and oxadiazole rings, the low-energy ones can be regarded as hybridized local and charge-transfer (HLCT) bands generated by overlapped localized and ICT π−π* electronic transitions between di-/triphenylamine and 1,3,4-oxadiazole, as we demonstrated in a previous work. 28 These transitions are well defined in solvents with moderate polarity, such as THF, as observed for M1 (Figure S8). The large blue shift of the HLCT band in the spectra of M1 compared to that of M2 suggests a lower π−π* electron delocalization along the diphenylamine-1,3,4-oxadiazole system compared to the triphenylamine-1,3,4oxadiazole framework.…”

“…The synthetic route and chemical structure of the diamine M1 is shown in Scheme 1, while diamine M2 resembling a 5-phenyl-1,3,4-oxadiazole-substituted triphenylamine structure (Figure S1, Supporting Information) was previously reported. 28 M1 was synthesized on the basis of aromatic nucleophilic substitution reaction in the presence of an acid buffer when 4-fluoronitrobenzene was coupled with 2-amino-5-(4-methoxyphenyl)-1,3,4-oxadiazole to give a dinitro precursor (M1′). Then, following the reduction reaction under mild conditions, the novel aromatic diamine with the chemical pattern composed of a diphenylamine substituted at the nitrogen atom with 2-(4methoxyphenyl)-1,3,4-oxadiazole was developed.…”

“…the second one is an 1,3,4-oxadiazole-substituted triphenylamine diamine (M2), which was reported in our previous work. 28 The diamine M1 was obtained in two steps as follows. In a 100-mL three-neck round-bottom flask equipped with a magnetic stirring bar, a nitrogen inlet and outlet, and a condenser, dinitro compound M1′ (1.5 g, 3.46 mmol) was suspended in a 50 mL mixture of ethanol/water (20:1).…”

Structural Chemistry-Assisted Strategy toward Fast Cis–Trans Photo/Thermal Isomerization Switch of Novel Azo-Naphthalene-Based Polyimides

“…On the other hand, the structural entanglement of these PIs is expected to be sensitive to the surrounding environment, especially to the solvent polarity. − When the electrons of a solvent can rearrange to stabilize the excited states of a molecule, the energy difference between the electronic levels of the molecule becomes lower and the absorption moves to a higher wavelength. This is also true for these azo-polymers in high polar solvents such as DMF that better stabilizes the dipolar species compared to those in less polar solvents, like CHCl 3 .…”

Opto-Electronic Properties Modulation Through Iodine Doping of Imine- and Triphenylamine-Based Oligomers

“…For this reason, the conjugated organic compounds offer a great alternative to conventional inorganic-based derivatives. [5][6][7][8][9][10] Among them, poly(imine)s, known as Schiff base polymers or poly(azomethine)s, are of great interest for both industry and academia due to their easy preparation and potential applications in electronics and opto-electronics. 11 Polyimines display interesting properties, like high thermal stability, fluorescence and electrochemical features, para-magnetism, resistance to high energy, liquid crystalline properties, and intrinsic conductivity, as well as complexation capability and biological activity.…”