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Cholesteric materials display unique optical properties which can be exploited in opto-electronic applications such as light emitting diodes. The key feature is the position of the wavelength of the emitted light relative to the one of the selective reflection band. We have synthesized a set of cellulose derivatives displaying the cholesteric phase with the aim to investigate the correlation between chemical structure and properties. Phase transition temperatures, the chain packing, the wavelength of selective reflection but also absorption and fluorescence spectra were investigated as a function of the degree of substitution (DS), the nature of lateral substituents, the composition of doped systems and blends of different cellulose derivatives. Investigated were furthermore the degree of circular polarization of the emitted light for guest–host systems and for cellulose systems with chromophores linked by covalent bonds to the cellulose backbone as well as their performance in light emitting diodes. The conclusion is that the optical properties can be accounted for on the basis of the model of a one-dimensional photonic crystal. The limiting factor with respect to opto-electronic applications is the poor control of the uniformity of the helix formation and orientation.

Butyric esters (BuPC) of hydroxypropylcellulose (HPC) with different degrees of substitution (DS) were obtained by the reaction of (2-hydroxypropyl)cellulose with butyryl chloride. Blends of these BuPCs were obtained from ternary solutions by removal of the com mon solvent. The blends displayed thermotropic choles teric mesophases and showed iridescent colors at ambient temperatures depending on the blend composition. The spectroscopic analysis of the blends showed systematic variations of the reflection colors with variations of the ratio of the blend components between the reflection colors of the pure blend components covering the range from 453-938 nm corresponding to pitch heights from 308 640 nm.

Guest host systems composed of various types of esters of (2-hydroxypropyl) cellulose and the chromophore coumarin 334 were characterized with respect ot the absorption and emission properties as a function of the concentration of the chromophore and the nature of the esters. The results were compared with the ones obtained for solutions of the chromophore with low molar mass solvents. The cellulose derivatives are characterized by good film forming capabilities, a high solubility for the chromophores, by significant solvatochromic effects both in absorption and emission and by the formation of excimers at elevated concentration of the chromophores. These features make such cellulose derivatives interesting candidates as matrix materials for host-guest systems in areas such as organic light emitting devices or sensors. Their tendency to display a cholesteric super-structure is of particular interest.

Butyric esters of (2-hydroxypropyl) cellulose (BuPC) with different degree of substitution (DS) were synthesized via control of the esterification time of butyryl chloride and (2-hydroxypropyl) cellulose. These BuPCs are thermotropic and displayed different colors at ambient temperature due to the formation of a cholesteric structure and the occurrence of a corresponding cholesteric reflection. The pitch height was found to increase significantly with a decrease of the degree of substitution. Both the glass transition temperature and the melting temperature are not affected by variation of the DS. The BuPC samples displayed a banded texture of focal-conic texture, respectively. The X-ray diffraction studies revealed the presence of a layer structure. The d-spacing between two adjacent layers in the cholesteric structure displayed no significant dependence on the DS in the range from 2 to 3.