A Multiswitchable Poly(terthiophene) Bearing a Spiropyran Functionality: Understanding Photo- and Electrochemical Control

Abstract

An electroactive nitrospiropyran-substituted polyterthiophene, 2-(3,3′′-dimethylindoline-6′-nitrobenzospiropyranyl)ethyl 4,4′′-didecyloxy-2,2′:5′,2′′-terthiophene-3′-acetate, has been synthesized for the first time. The spiropyran, incorporated into the polymer backbone by covalent attachment to the alkoxyterthiophene monomer units, leads to multiple coloured states as a result of both electrochemical isomerization of the spiropyran moiety to merocyanine forms as well as electrochemical oxidation of the polyterthiophene backbone and the merocyanine substituents. While electrochemical polymerization of the terthiophene monomer could occurs without the apparent oxidation of the spiropyran, the subsequent electrochemistry is complex and clearly involves this substituent. In order to understand this complex behaviour, the first detailed electrochemical study of the oxidation of the precursor spiropyran, 1-(2-hydroxyethyl)-3,3-dimethylindoline-6'-nitrobenzospiropyran, was undertaken, showing that, in solution, an irreversible electrochemical oxidation of the spiropyran occurs leading to reversible redox behaviour of at least two merocyanine isomers. With these insights, an extensive electrochemical and spectroelectrochemical study of the nitrospiropyran-substituted polyterthiophene films reveals an initial irreversible electrochemical oxidative ring opening of the spiropyran to oxidized merocyanine. Subsequent reduction and cyclic voltammetry of the resulting nitromerocyanine-substituted polyterthiophene film gives rise to the formation of both merocyanine π-dimers or oligomers and π-radical cation dimers, between polymer chains. Although merocyanine formation is not electrochemically reversible, the spiropyran can be photochemically regenerated, at least in part, through irradiation with visible light. SEM and AFM images support the conclusion that the bulky spiropyran substituent is electrochemically isomerizes to the planar merocyanine moiety affording a smoother polymer film. The conductivity of the freestanding polymer film was found to be 0.4 S cm -1 .3

Porous self-protonating spiropyran-based NIPAAm gels with improved reswelling kinetics

“…Amplitude sweep measurements in Figure 2a show that the blank gel has a higher viscoelastic modulus (15)(16)(17)(18)(19)(20) kPa) compared to the 20k porous gel with a modulus of 6 -7 kPa and the least stiff 2k porous gel …”

“…The closed, colourless, hydrophobic form referred often as benzospiropyran and the open, coloured, charged merocyanine form. The molecules can be switched between these two forms by light irradiation (photochromism) [15][16][17], electrochemical stimulation (electrochromism) [17][18][19][20], or changing the solvent environment (solvatochromism). [17,21] As a result of these unique properties, spiropyrans have been used, in combination with many different materials, for the fabrication of both sensors, actuators and stimulus responsive materials.…”

Copolymerisation as a way to enhance the electrochromic properties of an alkylthiophene oligomer and a pyrrole derivative: copolymer of 3,3′″ dihexyl-2,2′:5′,2″:5″,2′″-quaterthiophene with (R)-(-)-3-(1-pyrrolyl)propyl-N-(3,5-dinitrobenzoyl)-α-phenylglycinate

“…It seems that a synergic behaviour occurs displacing both the oxidation potential of the DNBP, even in higher proportion of DNBP in the mixture, as well as the E pa and E pc of the copolymer when compared with each homopolymer. This effect can be explained by the diminution of the steric hindrance caused by the voluminous groups present in DNBP and by the lateral alkyl chains present in DHQT [5,42].…”

“…However, the structural modification of these conjugated polymers with the aim to improve their properties is still a challenge. For example, the introduction of large functionalities onto a conjugated polymer can lead to a significant steric effect on the polymer backbone, adversely affecting the optical and electronic properties of the polymer [5,6]. Otherwise, copolymerisation is an easy, facile method to combine the electrochromic properties of monomers and it is a common approach to obtain materials with tailored properties [7,8].…”

Dual-color Multiresponsive Rhodamine Derivative and its Photochromic Enhancement Behavior in Polyurethane

“…Environment-sensitive materials are becoming increasingly attractive owing to their potential applications in molecular switches, [1][2][3][4] logic gates, [5] optical data storage, [6] optoelectronic devices, [7] controllable drug delivery, [8] etc. Compared to the monotone sensitive type, the environment-sensitive materials have been developed to various sensitive types including light, electricity, force, gas, magnet, and chemical compounds.…”