Abstract
Improvement in the first hyperpolarizability (βHRS) as well as intrinsic hyperpolarizability (βint) of chromophores based on 9,9-dimethyl-9H-fluoren-2-amine through modulation of the conjugation pathway is described. A series of six novel chromophores with "linear" conjugation showed significant enhancement of βHRS as well as βint compared to the counterparts lacking a "linear" conjugation but having an identical combination of donor, acceptor, and the intervening π-conjugated linker. The hyperpolarizability (βHRS as well as βint) values of the new series measured using hyper-Rayleigh scattering exceeded the apparent limit set by the latter set of fluorene-based chromophores. The experimental results are analyzed and interpreted in the context of linear optical properties, single-crystal X-ray analysis, electrochemistry, etc. and corroborated by theoretical studies. We find that modulation of the "push-pull" of the conjugation pathway in these donor-acceptor chromophores compares favourably with the corresponding changes in the optical gaps, transition dipole moments, and dipole moment difference between the ground and excited states.
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