Synthesis and Excimer Formation Properties of Electroactive Polyamides Incorporated with 4,5-Diphenoxypyrene Units

Abstract

A new dietherpyrene-cored diamine monomer, namely, 4,5-bis(4-aminophenoxy)pyrene, was successful synthesized and formed a series of electroactive polyamides with an aryloxy linkage in a polymer main chain and bearing pyrene chromophore as a pendent group using conventional one-pot polycondensation reactions with commercial aromatic/aliphatic dicarboxylic acids. The resulting polyamides exhibited good solubility in polar organic solvents and, further, can be made into transparent films. They had appropriate levels of thermal stability with moderately high glass-transition values. The dilute NMP solutions of these polyamides exhibited pyrene characteristic fluorescence and also showed a remarkable additional excimer emission peak centered at 475 nm. Electrochemical studies of these polymer films showed that these polyamides have both p- and n-dopable states as a result of the formation of radical cations and anions of the electroactive pyrene moieties.

Keywords: electroactive polymers; excimer emission; high performance polymers; polyamides; pyrene.

Scheme 1

Synthetic routes to pyrene-cored diamine (3).

Scheme 2

The postulated oxidation mechanism pathways of pyrene using RuCl₃/NaIO₄ catalytic system.

Figure 1

FT-IR spectra of pyrene-derived compounds and monomers 1–3.

Figure 2

(a) Proton and (b) carbon NMR spectra (enlarge region between 110 to 132 ppm as shown in red frame) of monomer 3 in DMSO-d₆.

Figure 3

(a) H-H COSY and (b) C-H HSQC NMR spectra of target monomer 3 in DMSO-d₆.

Figure 4

(a) Conclusive structure of diamine 3 using single-crystal X-ray analysis and the (b) front view and (c) side view of single-crystal lattice with cross-section profiles.

Scheme 3

Synthesis of dietherpyrene-based polyamides and their foldable films before and after irradiated by laboratory UV lamp at wavelength of 365 nm.

Figure 5

Representative TGA and DSC traces of polyamide 5c.

Figure 6

(a) Absorption and emission spectra of selected polyamides and pyrene in NMP solution (10 μM). (b) Photograph images were taken under illumination both of the dilute solutions and polymer films of a 365-nanometer UV light.

Figure 7

Absorption spectra of polyamides 5a and 5b in NMP solution (10 μM) and solid films coated on quartz glass.

Figure 8

PL spectra of the dilute solution of model compound (a) M1 and (b) M2 (ca. 10 μM) in solvents of various polarity. Photographs were taken under illumination of a 365-nanometer UV light.

Figure 9

Cyclic voltammograms of the polyamide 5a film on ITO-coated glass substrate in 0.1 M Bu₄NClO₄/CH₂Cl₂ (for oxidation trace) and DMF (for reduction trace) solutions at a scan rate of 50 and 100 mV/s, respectively.

Scheme 4

Presumed redox chemistry of dietherpyrene-containing polyamides.

Figure 10

Cyclic voltammograms of 500 μM of the model compound M2 in 0.1 M Bu₄NClO₄/CH₂Cl₂ (for the oxidation process) solutions at a scan rate of 50 mV/s.

Scheme 5

Proposed structures of electro-generated dimers of model compound M2.

Figure 11

Absorption, transmittance spectra and inset images of the 500 μM model compound M2 in 0.1 M Bu₄NClO₄/CH₂Cl₂ before and after continuous 50 cycles of CV test at a scan rate of 50 mV/s.