Large third-order nonlinear optical response from molecules with effective multidirectional charge-transfer transitions: New design of third-order nonlinear chromophores
✍ Scribed by Daniel R. Greve; Steen B. Schougaard; Dr. Tommy Geisler; Dr. Jan C. Petersen; Dr. Thomas Biørnholm
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 261 KB
- Volume
- 9
- Category
- Article
- ISSN
- 0935-9648
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✦ Synopsis
Elucidating the relationship between electronic structure and the first and second molecular hyperpolarizabilities, p and 7, respectively, is of major importance in the quest for organic materials sufficiently optically nonlinear for applications in electro-optical and all-optical devices.['-31 For dipolar molecules, large values of the first molecular hyperpolarizability, j, have been achieved and the underlying mechanism has been verified within the framework of the two-level model.[4951 It has recently been shown that octupolar molecules, e.g., 1,3,5-triamino-2,4,6-trinitrobenzene, are potent p alternative^,[^-^] demonstrating that, in addition to molecules with unidirectional charge-transfer lransitions, molecules with multidirectional charge-transfer transitions may also have large p values. Systems displaying high values of y have mainly been confined to quasi onedimensional systems, such as polyene-like and cyanines, ["] where the nonlinearity arises from the conjugated and highly polarizable x-electron backbone. Saturation phen~mena,['~"~] red shifts in the electronic transitions, and Peierls instabilities[151 have hampered efforts to further improve these systems. Identification of new, alternative design criteria is therefore exceedingly important for further development of the field.
Very recently large y-values have been found in donoracceptor-substituted tetraethynylethene~,['~l demonstrating the importance of full two-dimensional conjugation and appropriate donor-acceptor conjugation paths.