Self Assembling Phenylene Vinylene Materials and Devices
Pralle, Martin Ulrich
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https://hdl.handle.net/2142/82940
Description
Title
Self Assembling Phenylene Vinylene Materials and Devices
Author(s)
Pralle, Martin Ulrich
Issue Date
2001
Doctoral Committee Chair(s)
Stupp, Samuel I.
Department of Study
Materials Science and Engineering
Discipline
Materials Science and Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Electronics and Electrical
Language
eng
Abstract
A new class of self assembling rodcoil molecules was recently synthesized and their solid state structure was rigorously characterized. These molecules have a triblock architecture with a rigid rod molecular compound coupled to a diblock coil composed of an oligomeric flexible spacer and a bulky coil. The molecular structure has integrated photonic properties resulting from phenylene vinylene segments in the rigid backbone of the rod segment. It has been found that these molecules aggregate spontaneously when cast from solution into discrete objects with dimensions on the order of a few nanometers. The driving force for this aggregation is the crystallization of rod segments. To probe structure-property relationships in these materials, piezoelectric measurements were carried out in films and spontaneous piezoelectric activity was demonstrated without prior poling procedures. Upon poling the net polarization was enhanced and piezoelectric activities equal to that of quartz were observed. By applying both positive and negative fields a hysteresis was observed suggesting that these materials exhibit ferroelectric character. Through novel synthesis a structure was synthesized in the author's laboratory modeled after the triblock but targeting a diode-like aggregate upon self assembly. The molecules contained emissive phenylene vinylene segments in the rod block and hole transporting triphenylamine groups in the coil. Through subsequent characterization it was shown that the formation of nanoaggregates is indeed governed by the molecular architecture rather than the specific chemical functions of the three molecular segments. Inspired by these supramolecular diodes, self assembled organic light emitting diodes were fabricated based on a different self assembly approach. Prior to annealing, electron microscopy clearly showed kinetically trapped phase separated films. However after annealing a bilayer arrangement was observed with the hole conducting oligomer on the hole injecting electrode and the emissive phenylene vinylene dendron segregated to the electron injecting metal, the desired self assembled state. (Abstract shortened by UMI.).
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