The present invention relates to a liquid thioether carboxylic acid ester, a process for the preparation of the liquid thioether carboxylic acid ester, an article comprising the liquid thioether carboxylic acid ester as well as a use of the liquid thioether carboxylic acid ester as a component or substantial part of an optical system, tunable lens, adaptive optical module and materials thereof, actuator, electro-active polymer, laser and all related products, optical liquid, cover glass, lens or container material, tiltable prism or optical calibration liquid or optical refractive index matching liquid and a use of the liquid thioether carboxylic acid ester as a component or substantial part of a color filter, window material, coating, varnish, lacquer, dye or pigment formulation, immersion liquid, ingredient or additive in a plastic material or ingredient or additive in a polymer.