We have made an attempt to study electrochemically induced modification of ITO/PANI electrode in tetra-fluoro-hydroquinone (4F-hydroquinone) solution. The conditions at which the host molecule (of 4F-hydroquinone) incorporates into polyaniline were investigated, and the modifications in PANI electrode were monitored by optical absorption spectra measurements.PANI films were exposed to three different modifying conditions: a long-cycle polarization in acid solutions (pH range 0.4-3.2, potential limits between -0.35 and 0.8V versus SCE) without and with 4F-hydroquinone added and a chemical interaction between PANI and 4F-quinone solution for different times at pH 6. We found that modification is a pH-dependent process and can only occur at pH above 3. Cyclic treatment in electrolyte containing 4F-hydroquinone at pH 3.2 leads to 4F-hydroquinone residue incorporation into the polymer backbone that can be viewed as a new optical absorption band of the polymer (550-600nm). Other optical transitions of PANI are also changed due to modification. A π-π * transition (320-350nm) is broader and seems to contain two components. A localized polaron absorption (435-450nm) is several folds more intensive in modified PANI. A conduction band absorption (800-820nm) shows a blue shift and this band still appears at potentials where the loss of conductivity has occurred for non-modified polymer. We have proposed that modification emerged from interaction of the acid polymer centers and 4F-hydroquinone molecules oxidized during cycling.