Effect of complexation on the photochromism of 5′-(benzothiazol-2-yl)spiroindolinonaphthooxazines in polar solvents

Complexation of Ni(II), Co(II) and Zn(II) with the photomerocyanines obtained under steady irradiation of spiroindolinonaphthooxazines containing benzothiazolyl substituent in the naphthooxazine moiety induces a slight hypsochromic shift of its visible absorption band and drastically slows down its thermal bleaching in the dark. As a result, the relaxation time at 20°C ranges from 2 to 42 min, the actual value depending on the metal ion and compound. High 'colourabilities' up to 5 × 104 M−1 cm−1 (ɛ = 6 × 104 M−1 cm−1) are calculated from the absorbance values obtained by extrapolation to t = 0 of the room temperature linearly descending kinetic curves ln A/t. Complexation with Ni(II), Co(II) and Zn(II) allows the spiroindolinonaphthooxazines to isomerize to their open-coloured form even under dark conditions giving a complex spectroscopically identical to the photoinduced product and greatly increasing its lifetime to several days.