Design and synthesis of quadrupolar A-D-A photon absorbing molecules: An investigation into their optical and bioimaging properties

We herein report on the design and synthesis and optical properties of 4 novel chromophores based on a quadrupole acceptor-donor-acceptor system. These quadrupoles were designed using a fluorene core, coupled to thienyl and thienyl acetylene bridges, to either two 3-dicycanovinylindan-1-ones or two 1,3-bis(dicyanomethylidene)-indanes as strong electron-withdrawing moieties. The structure-property relationships were investigated by computational modelling and photophysical studies, with the fluorophores giving red-emission with large Stokes shifts. The bridged alkynyl units, rather than enhancing conjugation, dramatically reduced fluorescence intensities and wavelength of emission. Notably, two-photon absorption studies revealed cross-section values of δ = 1720 and 780 GM for two of the fluorophores. The fluorophores were explored in one-photon and two-photon fluorescence biological imaging, including the staining of chick bones. Herein we report on the synthesis and optical properties of four novel acceptor-donor-acceptor fluorophores and their biological applications. • Design and synthesis and optical properties of 4 novel chromophores based on a quadrupole acceptor-donor-acceptor system. • Fluorophores had very large Stokes shifts. • Two-photon absorption studies revealed cross-section values of δ = 1720 and 780 GM for two of the fluorophores. • The fluorophores were explored in one-photon and two-photon fluorescence biological imaging.