Ionochromic response

Marsella MJ, Swager TM (1993) Designing conducting polymer-based sensors - selective ionochromic response in crown-ether containing polythiophenes. J Am Chem Soc 115 12214-12215... 

Marsella and Swager have studied conducting-polymer-based sensors for selective ionochromic response [126]. For example, the polymer (molecular weight 2800) depicted in Figure 98 showed a Al of 15 nm, 63 nm and 10 nm in the presence of Li, Na and K, respectively. 

Marsella, M.J., R.J. Newland, and T.M. Swager. 1995. The ionochromic response of crown ether and calix[4]arene substituted polythiophenes Towards chemoresistive sensory materials. Polym Prep... 

Polymer 26 does exhibit ion-binding properties, and an ionochromic response occurs upon exposure to Li" in acetonitrile and leads to a blue shift of up to 11 nm [75]. A dramatic chemoselective response to Pb in... 

Many experimental results have suggested that the conformational modification of the polythiophene backbone can be induced through order-disorder transitions of the side-chains [59]. It was then postulated that various external stimuli could pertuib the side-chain organization and consequently induce some chromic effects. These side-chain transitions can be induced by heating (thermochromism), varying the solvent quality (solvatochromism), ion complexation (ionochromism), photo-induced isomerization (photochromism) and affinity binding (affinity or biochromism) giving rise to a novel class of field responsive materials. 

In contrast, ionochromic effects were visible with head-to-tail poly[3-(2,5,8-trioxanonyl)thiophene] poly(6) both in solution and in the solid state [24 249]. With the addition of cations such as Pb " and Hg " ", the conjugation of this polymer, characterized by an absorption maximum at 439 nm in CHCI3 and 486 nm in the solid state, was completely eliminated [247]. Thus, the cationic complexation would induce the twisting of the polymer backbone away from planarity. However, although the response was chemoselective (Li+ and Zn + were found not to interfere), the ionochromic effects observed with Pb + and Hg " " were irreversible, as the conjugation of the polymer was not restored after the complexation. 

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