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A new organo-inorganic hybrid electrochromic material poly(cyclotriphosphazene-4,4 0 -bipyridinium)chloride salt was synthesized wherein each phosphorus atom in the triphosphazene core is linked by diquaternized 4,4 0 -bipyridyls (PPBP). The electrochrome was characterized by 31 P nuclear magnetic resonance, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy (XPS). XPS confirmed the formation of P-N + and P-N linkages in the PPBP and the conversion of covalently bound Cl to ionic Cl À species. The transparent PPBP material undergoes three reversible one electron-transfer reactions to yield a radical cation insoluble film which first acquires a purple hue and then turns deep blue. Electrochromic devices were constructed with the PPBP hybrid dissolved in a highly conductive, thermally stable and electrochemically inert ionic liquid based gel electrolyte and a Prussian blue (PB) layer as the anode. The PPBP-PB device showed an extremely large coloration efficiency of 504 cm 2 C À1 , an exceptionally high transmission modulation of 70.5% at 590 nm, one among the highest reported contrasts in organic electrochromics, a large reflectance contrast of 59.2% at 545 nm and fast switching kinetics. The device was durable as it retained 96.2% of its original transmission after 1000 color-bleach cycles, thus exemplifying its use for both reflective and transmissive electrochromic applications.Electrochemical impedance studies revealed charge transfer to be a less resistive process during reduction relative to oxidation which cumulatively ensues in shorter coloration times. Our studies demonstrate the yet untapped potential of the inorganic (PNCl 2 ) 3 in steering the synthesis of new organo-inorganic hybrid materials, capable of undergoing facile redox phenomena, manifesting in unequalled functional properties and thereby offering opportunities to use this trimer for preparing a whole gamut of new high performance electroactive compounds.

Polymer electrolytes were synthesized by two different approaches and applied to electrochromic devices based on electrodeposited tungsten oxide (WO 3) or poly(3,4-ethylenedioxythiophene) (PEDOT) films as the cathode, and a Prussian blue (PB) film as the anode. The first method involved the entrapping of an ionic liquid in a polymer host (poly(methylmethacrylate) or PMMA) and the second approach relied on the in situ thermal polymerization of methylmethacrylate (MMA) in the hydrophobic ionic liquid, yielding a solidified transparent gel. The effect of in situ solid polymer electrolyte formation on device performance characteristics was realized in terms of a larger coloration efficiency of 119 cm 2 C 21 (l = 550 nm) achieved for the WO 3-PB (MMA) device, as compared to a value of 54 cm 2 C 21 obtained for the WO 3-PB (PMMA) device. Similar enhancements in electrochromic coloring efficiency, reflectance contrast, and faster switching kinetics were obtained for the PEDOT-PB (MMA) device. The strategy of introducing an electrolyte to the electrochromic device in a liquid state and then subjecting the same to gradual polymerization allows greater accessibility of the electrolyte ions to the active sites on the electrochromic electrodes and superior interfacial contact. As a consequence, larger optical contrast and faster kinetics are achieved in the MMA based devices. While PEDOT films were amorphous, PB films were semi-crystalline but only in the case of WO 3 ; the hexagonal structure of WO 3 , equipped with three/four/six-coordinated voids was found to affect bleaching kinetics favorably. The performance of PMMA based electrolyte is limited by high resistance at the electrode-electrolyte interface, and a smaller number of ions available for oxidation and reduction. Large area (y10 cm 6 4 cm) devices were also fabricated using this simple wet chemistry method and their ability to color uniformly without any pinholes was demonstrated.