Synthesis and Properties of a Novel Cross-Linked Electroactive Polymer Formed from a Bipolar Starburst Monomer

Abstract

This Article describes the synthesis and physical properties of two bipolar starburst monomers: 1,3,5-tris{5-(7-(carbazol-9-yl)-(9,9′-spirobifluoren-2-yl)-1,3,4-oxadiazol-2-yl}benzene (OXD-CBZ) and 1,3,5tris[7-diphenyl-(9,9′-spirobifluorene)-1,3,4-oxadiazoyl]benzene (OXD-DPA) featuring an electron-deficient tris(1,3,4oxadiazole)phenylene ring as an interior core bridged by rigid spirobifluorene units to terminal electroactive carbazole (CBZ) and diphenylamino (DPA) groups. The electronic absorption spectra of OXD-CBZ and OXD-DPA depend only slightly on the solvent polarity, revealing that weak electronic coupling existed between the donor (CBZ and diphenylamino groups) and acceptor (1,3,4-oxadiazole) moieties in the ground state. In contrast, the emission spectra of these starburst bipolar molecules were strongly dependent on the solvent polarity, a phenomenon that we attribute to the polarized excited states generated through intramolecular charge transfer. The starburst monomer OXD-CBZ exhibited a redox gradient, where the peripheral CBZ moieties exhibited lower oxidation potentials than those of the fluorene units in the interior, allowing us to obtain a new electropolymerized macromolecule. The polymer films derived from OXD-CBZ exhibited good conductivity, reversible electrochemical processes, and stable color changes (from transparent to green to light blue) with high coloration efficiency upon electro-oxidation. The radical cations of OXD-CBZ were localized within the CBZ rings; the lack of substituents at the C3 and C6 positions of the CBZ unit led to the effective electrochemical cross-linking process. In contrast, electro-oxidation of OXD-DPA, which was end-capped with DPA groups, produced stable radical cations that did not undergo associated electrochemical reactions. The higher stability of the OXD-DPA radical cations through resonance stabilization with the fluorene ring impeded the progress of typical triphenylamine dimerization reactions.

Electrosynthesis of Aromatic Poly(amide-amine) Films from Triphenylamine-Based Electroactive Compounds for Electrochromic Applications

“…The formed radical cation dimerizes and upon abstraction of two protons yields tetraphenylbenzidine (TPB) [ 36 , 37 ]. The electrochemical coupling reaction of TPA has been used as a convenient and effective method to prepare electroactive polymers for optoelectronic applications [ 38 , 39 , 40 , 41 , 42 , 43 ]. Systematic studies on the electrochemical oxidative coupling of carbazole have been reported by Ambrose and Nelson [ 44 , 45 ].…”

Facile Synthesis of Electroactive and Electrochromic Triptycene Poly(ether-imide)s Containing Triarylamine Units via Oxidative Electro-Coupling

“…It is well-known that unprotected triphenylamine (TPA) and N -substituted carbazoles such as N -phenylcarbazole (NPC) undergo electro-oxidative coupling (dimerization) to tetraphenylbenzidine (TPB) and N , N ′-disubstituted 3,3′-bicarbazyls, respectively [ 28 , 29 ]. With appropriately designed monomers, the TPA or carbazole electrochemically oxidative coupling reaction could be employed as an efficient polymerization method to fabricate electroactive polymer films with potential applications in optoelectronic devices [ 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 ]. In recent years, we have demonstrated that electrochromic polyamide and polyimide films could be facilely synthesized from the amide- or imide-preformed compounds with terminal TPA or NPC groups through oxidative electro-coupling polymerization [ 38 , 39 ].…”

Synthesis and Properties of an Electropolymer Obtained from a Dimeric Donor/Acceptor System with a 4,4′-Spirobi[cyclopenta[2,1-b:3,4-b′]dithiophene] Core

“…Both electrochemical and spectroscopic data thus indicate that the introduction of one extra C−C double bond between the TPA moiety and the cyclopentadithiophene unit effectively increase the conjugation length in SO# dyes with significant consequences on the radical cations delocalization, as previously observed for related molecular systems. 10,11 Spectroelectrochemical Characterization of the Electrogenerated Film. In order to study the optical characteristics of the electropolymer generated from SO1 and to identify the species involved in the electrochemical processes in the organic film, a SO1 polymeric thin film was formed over a semitransparent conductive electrode (ITO).…”

“…10,17,22,49 Thus, the blue-shift observed for the ITC transition in the film can be reasonably ascribed to the changes in the surrounding environment, originated in the solid state embedded in an electrolyte solution. 10,11,17,22 At the onset of the oxidation process the film presents a small increment of absorbance in the wavelength zone of 425−475 nm and a bleaching of the band at higher energy (λ max ≈ 360 nm). This effect can be fully appreciated in Figure 7b.…”