Photofading, photosensitization and the effect of aggregation on the fading of triphenodioxazine and copper phthalocyanine dyes on cellulosic film

The photosensitized oxidation of four triphenodioxazine (TPDO) reactive dyes and a copper phthalocyanine (CuPc) reactive dye on cellulosic films by Rose Bengal (RB) was examined in aqueous solution under aerobic conditions. The rates of photooxidation of 4,11-bis(vinylsulfonyl)TPDO dyes were smaller than those obtained for 3,10-bis(disubstituted triazinyliminoethylimino)TPDO dyes. The rates of photofading of the four TPDO dyes and a CuPc dye on cellulose were similar in the order to the rates of the photosensitized oxidative fading with RB. Photo-oxidation left the aromatic residue from TPDO ring along with the reactive anchor bound to cellulose. No aggregation effect was observed on the fading of TPDO dyes and a CuPc dye on cellulose. The photosensitivity of the TPDO dyes was very small, this being estimated by the photosensitized fading of an aminopyrazolinylazo dye (Yellow dye) on cellulosic films dyed in admixture with TPDO dyes by use of a yellow filter to shield Yellow dye on exposure. It is concluded that the good light-fastness of the TPDO dyes on cellulosic substrate is attributed to the very small photosensitivity in spite of their relatively large ease with which they are oxidized.