Untersuchungen zur Thermochromie von Heterospiranen und Farbbildnern mit heterocyclischen Teilsystemen und O oder N als Ringschlussatom

Investigations on the Thermochromism of a Series of Spirocyclic Compounds and ‘Colourformers’ with Heterocyclic Parts and O or N as the ‘Key’ Atom . The thermochromism of a series of spirocyclic compounds with heterocyclic parts and O or N as the ‘key’ atom and of ‘colourformers’ was investigated in different solvents such as benzyl alcohol, dimethyl phthalate, decaline, toluence, or xylene. Thermodynamic data for the involed equilibria (Δ H °, Δ S °, and Δ G ° 298k ) and VIS‐spectroscopic data were determined and discussed in relation to the ones known spiropyrances. Compounds with O as ‘key’ atom behave very similary to the known spiropyrances, compounds with N as ‘key’ atom mostly are unstable undergoing irreversible bleaching. The ‘colour formers’ usually show only small thermochromic effects and very small equilibrium concentration of the coloured form.