Electrochromism is at once a solved and an unsolved problem: electrochromic (EC) glazing is commercial and can save 20–40% of building energy for lighting and climate control, yet few devices switch in seconds, show more than one colour or survive a decade of use [1,2]. This lecture follows the field from molecular redox processes to multifunctional devices, centred on conducting polymers and organic electrochromics. Transition-metal oxides set the benchmark for robustness but also the ceiling: single colour, slow ion insertion and modest coloration efficiency (CE ≈ 35 cm² C⁻¹ for WO₃). In anodic Nb₂O₅, optical and current transients are governed by the same ion–electron pair diffusion [3], and the electrolyte matters as much as the film: a protic ionic liquid enables proton insertion into nanostructured WO₃ without dissolution [4]. Conducting polymers offer CE of 300–600 cm² C⁻¹, multicolour from a single film and sub-second switching in polymer/oxide hybrids [2]. Yet colour does not simply follow charge: in polyaniline, chromogenic relaxation lags charge injection because benzenoid–quinoid conformational changes are slower [5].
Increasingly, the device, not the chromophore, limits performance. Gel electrolytes for reversible Bi electrodeposition [6], viologen ionogels [7] and viologen-functionalised poly(ionic liquid)s that merge chromophore and electrolyte [8] show how ion transport, mechanics and interfaces are set by the surroundings. Material reversibility (>10⁴ cycles) does not guarantee shelf durability: the calendar life of cycling-stable organic films can be below ten days, whereas in-situ photocured EC materials exceed 120 days [9]. Finally, I will discuss multifunctional devices combining optical modulation with energy storage, self-powering and deformable formats [10], and argue for unified benchmarking: ΔT, CE, switching times, cycle and calendar life at stated wavelength and area.
 

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