Design, synthesis, and characterization of new organic dendrimers with greatly enhanced two-photon absorption

Dendrimers have unique highly branched repeating structures that display intriguing processing and photonic properties. We have recently synthesized several generations of a new dendrimer series based on bis-(diphenylamino)-E-stilbene repeat units which have proven to be highly processible in common organic solvents, and which can be designed and synthesized in either three-arm or four-arm structural motifs. We have measured the dependence of the two-photon absorption (TPA) on excitation wavelength for the G-0, G-1 and G-2 generations of these monodisperse macromolecules, and have shown that the maximum value for the intrinsic TPA cross-section for femtosecond pulses inceases in proportion to the total number of stilbene chromophores, and yields a record high cross-sectrion for the G-2 dendrimer (11,000 GM units). We have now been able to incorporate a variety of electron donor and acceptor substituents in the three-arm dendrimer G-0 system to establish structure-property relatiuonships for the further enhancement of the intrinsic two-photon cross-sections. We have found a dramatic enhancement of the two-photon cross-sections for these dendrimers compared to the parent bis-(diphenylamino)-E-stilbene (BDPAS). In the 3-arm G-0 series, the intrinsic TPA cross-section, measured at the TPA maximum, varies from 1,400 to 1,900 GM units compared to 130 GM units for BDPAS, a more than 10-fold enhancement, while the number of BDPAS repeat units in the G-0 dendrimer is only 3 times the parent BDPAS structure.