Supramolecular ring banded prototype liquid crystalline oligo(phenylenevinylene).
We report a new ring banded supramolecular structure in thermotropic liquid crystalline oligo(phenylenevinylene) (OPV) via a melt crystallization process. A series of structurally different OPV molecules were synthesized using tricyclodecanemethanol (TCD) as a bulky pendant unit to trace ring banded morphology. Among all, an OPV molecule with rigid bis-TCD units in the central core and flexible dodecyl chains at the outer phenyl rings (BTCD-BDD-OPV) was found to show ring banded morphologies, which is a first of its kind in pi-conjugated materials. BTCD-BDD-OPV experiences strong aromatic pi-pi interactions in both film and liquid crystalline (LC) frozen stage. The pi-induced aggregation leads to lamellar self-assembly of OPV-mesogens that subsequently undergo helical crystal growth, thereby producing dark and bright ring banded patterns. Variable temperature X-ray diffraction analysis revealed the existence of three peaks at 27.07, 13.97, and 8.90 A corresponding to 001, 002, and 003 fundamental layers, respectively, thus confirming the lamellar self-assembly of OPV-mesogens. Electron microscopic (SEM and TEM) analysis of the LC frozen sample showed images confirming helical microcrystalline assembly and providing direct evidence for the self-organization mechanism. Detailed photophysical experiments such as excitation, emission, and time-resolved fluorescence decay studies indicated that BTCD-BDD-OPV has very strong pi-pi interaction in both film and LC frozen stage, which was found to be main driving force for the formation of supra-ring structure. Upon illumination with light, the OPV chromophores in the LC phase were excited and the color of the samples turned into luminescent green ring bands.
Amrutha
S R
SR
Chemical Sciences & Technology Division, National Institute for Interdisciplinary Science and Technology, Thiruvananthapuram 695019, Kerala, India.
Jayakannan
M
M
D050866:Liquid Crystals / Q000737:chemistry*; D046911:Macromolecular Substances / Q000737:chemistry; D015394:Molecular Structure; D010316:Particle Size; D011145:Polyvinyls / Q000138:chemical synthesis / Q000737:chemistry*; D013696:Temperature
D046911:Macromolecular Substances; D011145:Polyvinyls; C530822:oligo(p-phenylene vinylene)