Optical evidence of electrochemical modification of polyaniline induced bytetra-fluoro-hydroquinone

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) incorporate s into polyaniline were investigated, and the modifications in PANI electro de were monitored by optical absorption spectra measurements. PANI films we re exposed to three different modifying conditions: a long-cycle polarizati on in acid solutions (pH range 0.4-3.2, potential limits between -0.35 and 0.8 V versus SCE) without and with 4F-hydroquinone added and a chemical int eraction 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 p H 3.2 leads to 4F-hydroquinone residue incorporation into the polymer backb one that can be viewed as a new optical absorption band of the polymer (550 -600 nm). Other optical transitions of PANI are also changed due to modific ation. A pi-pi* transition (320-350 nm) is broader and seems to contain two components. A localized polaron absorption (435-450 nm) is several folds m ore intensive in modified PANI. A conduction band absorption (800-820 am) s hows a blue shift and this band still appears at potentials where the loss of conductivity has occurred for non-modified polymer. We have proposed tha t modification emerged from interaction of the acid polymer centers and 4F- hydroquinone molecules oxidized during cycling. (C) 2001 Elsevier Science B .V. All rights reserved.