Synthesis and Nonlinear Optical Behavior of Thermally Stable Chromophores Based on 9,9-Dimethyl-9H-fluoren-2-amine: Improving Intrinsic Hyperpolarizability through Modulation of Push-Pull

Improvement in the first hyperpolarizability (beta HRS) as well as intrinsic hyperpolarizability (beta int) of chromophores based on 9,9-dimethyl9H-fluoren-2-amine through modulation of the conjugation pathway is described. A series of six novel chromophores with linear conjugation showed significant enhancement of beta HRS as well as beta int compared to the counterparts lacking a linear conjugation but having an identical combination of donor, acceptor, and the intervening pi-conjugated linker. The hyperpolarizability (beta HRS as well as beta int) 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.

Automated summary

This study describes the improvement of first hyperpolarizability and intrinsic hyperpolarizability of chromophores based on 9,9-dimethyl9H-fluoren-2-amine through modulation of the conjugation pathway. Experimental results show that the novel chromophores with linear conjugation exhibit higher hyperpolarizability compared to counterparts without linear conjugation but with the same combination of donor, acceptor, and linker. The theoretical studies confirm the experimental findings and suggest a correlation between modulation of the conjugation pathway and optical properties.