The aim of this work is to develop novel functional materials based on benzimidazole derivates. A new irreversible chemical optical sensor (optode) - a chemodosimeter for mercury detection based on the fluorescence response of benzimidazole, 2-N-piperidinylbenzimidazole[1,2-a]quinoline-6-carbonitrile immobilised in the polymer matrix was prepared. The sensing mechanism is based on the formation of ionic pair of the selected benzimidazole derivative and the lipophilic anionic salt, tetrachlorophenyl borate. The benzimidazole derivate is fluorophore responsible for the formation of the analytical signal, whilst lipophilic anion (borate salt) is the sensing part of the optode, responsible for the detection of mercury ions in the measured sample (receptor for mercury ions). Borate salt in the presence of mercury ions is decomposed, and at the same time, the ionic pair of Fluorophfore+Receptor- is disintegrated after which the benzimidazole fluorophore deprotonates for balancing charge in the polymer membrane. By deprotonating, the fluorophore changes its photophysical properties, or the fluorescence intensity increases (turn-on senor). Thin film on a transparent carrier, optode, was prepared by spin coating technique, immobilising fluorophore and anionic borate salt in a plasticized PVC matrix. The influence of pH and the optimum pH range for the best fluorescence response of the optode was investigated. The mechanism of sensing activity, the range of concentrations in which the optode can be used for mercury detection in the solution, the response time, the stability in the buffer and the selectivity of mercury was described. The optode is characterized by UV-visible absorption and fluorescence spectrophotometry. A chemical optical sensor for mercury detection has been successfully developed in the concentration range of c = 5*10^-4 M to c = 1*10^-6 M. During the detection of mercury, in the sensor, there are irreversible chemical changes that define it as a chemodosimeter. Interferences with other metals were investigated where the greatest deviation of the analytical signal from the reference signal was about 12%. Sensor showed good stability within a 15-minute sensory activity.