Large First Hyperpolarizabilities in Push-Pull Polyenes by Tuning of the Bond Length Alternation and Aromaticity

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Abstract
Conjugated organic compounds with 3-phenyl-5-isoxazolone or N,N'-diethylthiobarbituric acid acceptors have large first molecular hyperpolarizabilities (β) in comparison with compounds with 4-nitrophenyl acceptors. For example, julolidinyl-(CH=CH)3-CH=N,N'- diethylthiobarbituric acid, which has 12 atoms between the donor and acceptor, has a β(0) of 911 x 10-30 electrostatic units, whereas (CH3)2NC6H4,–(CH=CH)4–C6H4NO2, with 16 atoms between its donor and acceptor, has a β(0) of 133 x 10-30 electrostatic units. The design strategies demonstrated here have resulted in chromophores that when incorporated into poled-polymer electrooptic modulators exhibited significant enhancements in electrooptic coefficients relative to polymers containing the commonly used dye Disperse Red-1. Poled polymer devices based on these or related chromophores may ultimately lead to high-speed electrooptic switching elements with low drive-power requirements, suitable for telecommunications applications.