Intrinsic luminescence properties of ionic liquid crystals based on PAMAM and PPI dendrimers

The photophysical properties of ionic liquid crystals based on poly(amidoamine) {PAMAM} and poly (propyleneimine) (PPI) dendrimers were examined both in solutions and in thin solid films. The dendrimers were peripherally modified by decanoic, 4-octyloxybenzoic, and 3,4,5-trioctyloxybenzoic acids to generate dendrimer based ionic liquid crystals of smectic and columnar phases. The liquid crystalline properties of these compounds were examined by polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). The dendrimer based ionic liquid crystals exhibited blue emission upon excitation at 370 nm. The emission intensity was found to be enhanced by an order of magnitude in solution when ionic liquid crystals are made from higher generation dendrimers. The steady state and time resolved fluorescence experiments suggest that optical properties of the liquid crystals are originated from the intrinsic emission properties of amine terminated PAMAM and PPI dendrimers. The findings presented here show for the first time that PAMAM and PPI based mesogenic structures can exhibit intrinsic emission in the visible region without incorporating conventional fluorophores.