The present invention disclose photochromic metal organic frameworks (MOFs) containing photochromic 1,4,5,8-naphthalenediimide (NDI) core and metal ions selected from Mg, Ca or Sr. The developed MOFs find application in inkless and erasable printing wherein they retain the photogenerated colour for a prolonged period of time so that the printed content remains legible/readable for reasonable time.

The present invention disclose photochromic metal organic frameworks (MOFs) containing photochromic 1,4,5,8-naphthalenediimide (NDI) core and metal ions selected from Mg, Ca or Sr. The developed MOFs find application in inkless and erasable printing wherein they retain the photogenerated colour for a prolonged period of time so that the printed content remains legible/readable for reasonable time.

The present invention disclose photochromic metal organic frameworks (MOFs) containing photochromic 1,4,5,8-naphthalenediimide (NDI) core and metal ions selected from Mg, Ca or Sr. The developed MOFs find application in inkless and erasable printing wherein they retain the photogenerated colour for a prolonged period of time so that the printed content remains legible/readable for reasonable time.

The present invention disclose photochromic metal organic frameworks (MOFs) containing photochromic 1,4,5,8-naphthalenediimide (NDI) core and metal ions selected from Mg, Ca or Sr. The developed MOFs find application in inkless and erasable printing wherein they retain the photogenerated colour for a prolonged period of time so that the printed content remains legible/readable for reasonable time.

A solution of a gallium phthalocyanine contains a compound of formula (1) and a gallium phthalocyanine of formula (2),
H.sub.2NCH.sub.2R.sup.1CH.sub.2NH.sub.2(1)
wherein R.sup.1 represents a single bond, or a substituted or unsubstituted alkylene group having 1 to 10 main-chain carbon atoms, a substituent of the substituted alkylene group is an alkyl group having 1 to 3 carbon atoms, an alkyl group having 1 to 3 carbon atoms and being substituted with an amino group, or a hydroxy group, one of the carbon atoms in the main chain of the alkylene group may be replaced with an oxygen atom, a sulfur atom, or a bivalent group represented by the formula NR.sup.2, and R.sup.2 represents a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, or an alkyl group having 1 to 3 carbon atoms and being substituted with an amino group, and ##STR00001##
wherein X.sup.1 represents a chlorine atom or hydroxy group.