Molecular engineering of chromophores for combined second-harmonic and two-photon fluorescence in cellular imaging

A series of chromophores with enhanced second-and third-order nonlinear optical properties were engineered for use in combined second-harmonic and two-photon fluorescence microscopy. Electronaccepting moieties imparted nonlinear optical properties to the chromophores. The electron-rich carbazole core served as a template towards one-or two-dimensional chromophores. More efficient acceptor groups (pyridinium, benzazolium, benzothiazolium) on the carbazole donor core resulted in improved second-and third-order nonlinear optical properties. A selection of these chromophores was tested in a cellular environment with a multimodal multiphoton microscope. The structural differences of the chromophores resulted in high selectivity for mitochondria or the nucleus in two-photon fluorescence and ranging from no signal to high selectivity for mitochondria in the SHG channel.