HEAT-INDUCED STRUCTURAL-CHANGES IN MEROCYANINE DYES - X-RAY AND THERMAL STUDIES

Certain merocyanine dyes undergo heat-induced isomerisation, which is responsible for their thermovoltage generation properties. Using these dyes, our studies reveal the correlation between their thermal proper ties and their crystalline structure. Differential thermal analysis of hexadecyl, decyl and pentyl dyes showed reversible phase transitions at their respective characteristic temperatures (T-c) owing to thermal isomerisation of the dyes. X-Ray diffraction patterns indicated heat- induced changes in the crystal structure of the dyes. This was also su pported by the results obtained from polarising microscopy studies and thermogravimetric analysis. Further heating of these dyes caused a pe rmanent deformation in the crystal structure, which ultimately led to total disintegration as recorded in the thermogravimetric studies.