Wydział Chemii

Marcin Piwowarczyk

Izabela Korbecka

Jerzy Sokolnicki

Natalia Osiecka-Drewniak

Mirosław Gałązka

Władysław Wrzeszcz

Zbigniew Galewski

2019

Phase Transitions

92

217-228

10.1080/01411594.2018.1563790

Naukowa

Angielski

Artykuł

Six new compounds were synthesized that have no alkyl chains in their structure: 4-nitrocinnonates of 4-hydroxyazobenzene, 4-nitro-4’-hydroxyazobenzene, 4-fluoro-4’-hydroxyazobenzene, 4-chloro-4’-hydroxyazobenzene, 4-bromo-4’-hydroxyazobenzene and 4-iodo-4’-hydroxyazobenzene. Using the polarizing microscopy and differential scanning calorimetry, enthalpies and temperatures of phase transitions were determined. All investigated compounds have an enantiotropic nematic phase. These compounds proved to be extremely thermally stable. Thermal decomposition was observed in temperatures above 300°C. Investigated compounds contain two different chromophore groups (i.e. azo and ethene moieties), which influenced the complex trans–cis isomerization processes of both groups (three time-separated processes were observed). It was shown that the presence of the ethene group significantly shifts the π-π* band towards higher energies. The substituent polarity in the azo group also affected the energy of this absorption band. A weak luminescence effect was observed in the 4-nitrocinnonates of 4-hydroxyazobenzene compound.

Azobenzenes, nematic, DSC calorymetry, Polarizing microscopy, trans-cis izomerization, luminescence

https://doi.org/10.1080/01411594.2018.1563790