Conjugated conducting polymers presenting both electrochromic and fluorescent properties have become one of the main research topics due to their notable advantages, such as low cost and simple production methods, processability, and the possibility of tuning the band gap (and the colour states) of the polymer by suitable choice of the monomer substituent [1] or by copolymerisation [2]. Oligothiophenes, such as terthiophene (TTh), constitute an interesting class of electroactive polymers with potential application in organic electronics that can be used as components of active layers for application in electronic devices such as Organic Light Emitting Diodes (OLEDs) and electrochromic devices. In order to modify the properties of TTh, this work has focused on the electrochemical copolymerisation of TTh with a pyrrole derivative, (R)-(-)-3-(1-pyrrolyl)propyl-N-(3,5dinitrobenzoyl)-α-phenylglycinate, DNBP. The polymer PDNBP has already been investigated by our group and presents good results concerning its application as an electrochromic material [3].

The copolymerisation of 3,3′″ Dihexyl-2,2′:5′,2″:5″,2′″-quaterthiophene (DHQT) and (R)-(-)-3-(1-pyrrolyl)propyl-N-(3,5-dinitrobenzoyl)-α-phenylglycinate (DNBP) was successfully performed electrochemically in acetonitrile (CH3CN) containing tetrabutylammonium tetrafluoroborate ((C4H9)4NBF4) by direct oxidation of monomer mixtures in different feed ratios. Copolymerisation improved the properties of the films of both polymers PDHQT and PDNBP, in respect to the adhesion of PDHQT onto ITO/glass surface and the chromatic contrast of these electrochromic materials. PDHQT, PDNBP and P(DHQT-co-DNBP) films were characterised by FTIR spectroscopy, fluorescence spectroscopy, Scanning Electron Microscopy (SEM) and spectroelectrochemical techniques. Solutions of PDHQT and its copolymers with DNBP (independently of the feed ratio) in N-methylpyrrolidone are fluorescent with emission bands at 555 and 585nm when excited at 375nm. Reversible changes in the hue and saturation occur in all the copolymer films from yellow or orange in the reduced state to green or blue in the oxidised state, but were dependent on the proportion of the comonomers used to prepare the copolymers. These changes are more significant for P(DHQT-co-DNBP) films deposited onto ITO/glass with 1:5 feed ratio, as shown by the track of the CIE 1931 xy chromaticity coordinates and by the electrochromic parameters in which this film (thickness 0.8±0.2μm) presented chromatic contrast (Δ%T) at 660nm of 62%, coloration efficiency (η) of 266cm2C−1 and stability to redox cycling (Δ%T=17% at the 1000th cycle). Therefore, these copolymers are potentially applicable in displays and optoelectronic devices as electrochromic and fluorescent materials.

A fluorescent pyrrole derivative bearing a dansyl substituent was prepared by a simple synthetic route and electropolymerized onto Indium Tin Oxide (ITO) electrodes. The presence of the dansyl group in the monomer precursor prevents the electropolymerization in usual systems, such as (C4H9)(4)NBF4 in acetonitrile (CH3CN). For this reason, it was added 20% boron trifluoride diethyl etherate (BFEE) to this system, to achieve electropolymerization. The resulting poly[3-(N-pyrrolyl)propyl dansylglycinate] (PPyPDG) films displayed electrochromic behavior. Their color varied from greenish-yellow, in the neutral state, to greyish-green, in the oxidized state; moreover PPyPDG is a good green light emitter material. Therefore, PPyPDG films might be potentially applicable in displays and optoelectronic devices. (C) 2013 Elsevier Ltd. All rights reserved.

A fluorescent polythiophene derivative bearing a donor-acceptor dansyl substituent was prepared by a simple synthetic route. Poly[2-(3'-thienyl)ethyl dansylglycinate] (PTEDG) is soluble in common organic solvents which allow the drop cast of films onto ITO electrodes. The electrochromic properties of these films were investigated and it was observed color variation from yellow, in the neutral state, to bluish-gray, in the oxidized state. Both the monomer 2-(3'-thienyl)ethyl dansylglycinate (TEDG) and its polymer PTEDG are, respectively, green and yellow light emitter materials. (c) 2013 Elsevier B.V. All rights reserved.

Copolymer films consisting of (R)-(-)-3-(1-pyrrolyl)propyl-N-(3,5-dinitrobenzoyl)-α-phenylglycinate (DNBP) and 3,4-(ethylenedioxy)thiophene (EDOT) were electrochemically deposited onto ITO electrodes and their electrochromic properties were investigated. Besides high absorption in the near infrared region, these films presented multielectrochromism with three different colors, being brown in the reduced state, green in the neutral state, and blue in the oxidized state. Spectrochronoamperometry data revealed that the copolymer films have fast switching time, high chromatic contrast, and high stability to redox cycling. The films also displayed lower band gap and better electrochromic properties as compared to the homopolymer PDNBP.

Dansyl-based fluorescent films were prepared by two different methods. In one of them, the surface of an indium tin oxide (ITO) electrode was coated with a film of chitosan and the polymer subsequently derivatized with dansyl chloride, whilst in the second method a film of dansylglycine was electrochemically deposited on the ITO surface. Atomic force microscopy (AFM) was employed to map the surfaces of the films. Comparison of the morphological, photochemical and electrochemical properties of these films indicated that the dansylglycine film electrodeposited on ITO exhibited electrochemical response, emitted a higher level of fluorescence, presented greater surface roughness and larger relative surface area in comparison with its dansyl chloride-chitosan counterpart. This behavior can be attributed to the higher number of active sites present in the well-organized and rough structure of the electrodeposited film in comparison with the chemically produced films.