Student Project Abstracts 2005 - Pluto - University of Washington

Synthesis of Dendron-Functionalized Chromophores:An Approach to Supramolecular Assembly for Electro-optic ApplicationsZerubba LeviGonzaga UniversitySei-Hum Jang and Alex JenDepartment of Materials Science and EngineeringUniversity of WashingtonINTRODUCTIONOrganic nonlinear optical (NLO) chromophores present anumber of applications in optical communication systems andstorage devices. Basic research efforts are aimed at pushing thebandwidths of optical networks to 80, 100 and even 160 GHzwith the use of novel organic chromophores. The application oforganic electronics to commercial devices demands the thermal,chemical, and photo-stability of the materials. Balancing the opticaltransparency while maximizing the nonlinear response andensuring accentric geometry of the chromophores in bulk materialsis also of critical importance.Recent work in the synthesis of NLO materials has extensivelyused dendrimers to reduce dipole-dipole interactions betweenchromophores through the site-isolation effect. As a result,much higher poling efficiencies, temporal alignment stabilitiesand nonlinear responses have been observed. In this project aseries of NLO chromophores were synthesized with the carefulselection of monolithic and binary dendron structures to producepre-aligned systems with the capacity for supramolecular assemblyupon electric field poling.Benzene and hexafluorobenzene (HFB) are known to cocrystalizein a face-to-face manner through several noncovalent associativeinteractions such as electrostatic quadrupolar interactions(see Figure 1). 1Recent efforts in the Jen group have provided solid stateevidence that arene-fluoroarene dendrons can produce supramolecularstructures. The results provided by the Jen group illustratechromophores capable of the arene-fluoroarene (Ar-Ar F )interactions produced enhanced r 33coefficients, T gvalues, andthermal stabilities relative to those chromophores that could onlyexhibit Ar-Ar or Ar F -Ar F interactions. This suggests the Ar-Ar Finteractions between monolithic dendrons ameliorate the polingprocess through π-π attractive forces that counteract the dipoledipoleforces among the chromophores. Despite the significantimprovements of the r 33coefficients of these systems over othermaterials, work still needs to be made to improve the thermalproperties of the materials.Figure 2. Chromophore functionalized with dendronsStudies using ab initio calculations performed with the DFTmethod indicate the cohesive energy of heterodimers (E c) increasesas the electron density of the π-donating system increases(see Table 1).HeterodimerE C(kcal/mol)Benzene/HFB 4-6Anthracene/HFB 7.7Pyrene/HFB 8.3Triphenylene/HFB 8.6Figure 1. Stacking arrangement of Benzene/HFB complex.Table 1. Cohesive Energies (E C) for Heterodimers 2,3CMDITR Review of Undergraduate Research Vol. 2 No. 1 Summer 2005 67