## 3 Results  
### Spectroelectrochemistry of the Devices  
The electrochemical properties of the thienoviological as well as that of the fluorene-diarylamine derivative in solution have been previously studied and reported by our group [33; 47; 48; 49]. Cyclic voltammetry (CV) of the polymer gel (EC gel) was performed on a ITO/EC gel/ITO sandwich cell without a reference electrode, in which two ITO coated glass plates served as working and counter electrodes (Figure S1). The CV of the device with the TV/Fc complementary components shows two redox processes in the negative scan, at potential biases (the potential difference between the two ITO electrodes) of 1.10 V and 1.30 V. The first one is relative to the reduction of the thienoviological dication (TV\({}^{++}\)) into the radical-cation (TV\({}^{++}\)) while the second is due to the formation of the neutral species (TV). The CV of the device containing the TV/FD system is more complex and this is mainly due to: (i) the higher numbers of processes involved and (ii) the overlap of the redox processes of the TV\({}^{\bullet+}\) and FD\({}^{\bullet+}\) species within the same range of potential bias (0.75 V \(<\Delta\)V \(<\) 2.0 V). In both devices therefore, the redox processes start at potential biases higher than about 0.75 V, above which huge spectral changes (electrochromism) should be expected. The electro-optical properties of these devices were investigated by spectroelectrochemical measurement (Figure 1). The spectroelectrochemistry of the TV/Fc EC gel shows that in absence of applied potential a strong absorption band is found at wavelength values \(<\) 500 nm, due to the \(\pi\)-\(\pi^{\bullet}\) transition of the TV\({}^{++}\) species [50]. Reduction to the radical cation species leads to the growing of a new broad band in the region 530-880 nm, and another in the range 1150-1700 nm (NIR region). Both these bands increase with the increase of the applied potential (Figure 1a). At about 1.7 V a partial bleaching of the NIR band at \(\sim\)1457 nm occurs (see the isosbestic point at 1370 nm) with the increase of a new absorption between \(\sim\)900-1300 nm. The application of a very small potential bias (\(\geq\)1.1 V) enables the device to absorb almost all the visible region being accompanied by a color change of the gel from yellow to black-green (Figure 1b). Replacement of the Fc\({}^{+}\)/Fc redox couple with the anodic FD, allows to broad the absorption range fully covering the near infrared region (NIR) up to 2000 nm (Figure 1c). This NIR band, starts to grow up for potential bias of 1.3 V, where oxidation to the MV radical cation (FD\({}^{\bullet+}\)) and reduction to the thienoviological radical cation (TV\({}^{\bullet+}\)) take place (Scheme 1). Therefore, the NIR absorption band extending from about 800 nm up to 2000 nm, is the result of the superposition of the NIR bands of the two radical cations above, which are attributed to inter-valence charge-transfer (IVCT) transitions typical for MV compounds [47]. At this potential, there is the concomitant rising up of another absorption band (confirmed by the absence of the isosbestic point)in the range 550-800 nm, due to the formation of the TV radical cation (TV\({}^{\bullet+}\)) on the ITO slide opposite to that where the FD oxidation occurs. **Scheme 1. ** Schematization of the formation of the radical cation species in the FD (**a**) and TV (**b**) mixed valence species. Figure 1: Spectroelectrochemistry of the ITO/EC/ITO device containing (**a**) the TV/Fc system and (**c**) the TV/FD as anode and cathode, respectively. Film thickness = 5 \(\upmu\)m. Color code according to the longer-wavelength NIR band.