Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
9586358 | Journal of Luminescence | 2005 | 15 Pages |
Abstract
We use wavelength tunable femtosecond pulses to measure intrinsic (simultaneous) two-photon absorption (2PA) and three-photon absorption (3PA) molecular cross section in two series of Ï-conjugated dendrimers built of identical 4,4â²-bis(diphenylamino) stilbene (BDPAS) and 4,4â²-bis(diphenylamino) distyrylbenzene (BDPADSB) repeat units. Record large 2PA cross sections, Ï2=10â46Â cm4Â s are obtained for the largest second-generation BDPAS-based dendrimer, as well as zeroth-generation 4-arm BDPADSB-based dendrimer. In both series, maximum 2PA cross section increases nonlinearly with the number of Ï-electrons, whereas for higher generations this dependence turns to linear one. 3PA cross section also increases nonlinearly with the size of the system in the series of BDPAS-based molecules, amounting a record large value, Ï3=10â79Â cm6Â s2, for the largest, second-generation dendrimer. We interpret these results in terms of direct inter-branch conjugation, which facilitates cooperative enhancement of the nonlinear-optical response. We propose a simple model which allows us to determine the effective size of coherent domains (extent of conjugation), which, in turn, determines the optimum dendrimer size for most efficient nonlinear response.
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Authors
M. Drobizhev, A. Rebane, Z. Suo, C.W. Spangler,