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Nonlinear Optical Characterization of Carbazole-derived Chromophores for Combined Second-harmonic and Two-photon Fluorescence Imaging
Stijn Van Cleuvenbergen, Koen Clays, Evelien De Meulenaere, Jos Vanderleyden, Wei-Qiang Chen, Mei-Ling Zheng, Xuan-Ming Duan, Sotiris Psilodimitrakopoulos and Pablo Loza-Alvarez

Carbazole-derived chromophores with enhanced second- and third-order nonlinear optical properties were engineered and characterized for their nonlinear optical properties, for ultimate use in combined second-harmonic and two-photon fluorescence microscopy imaging. Electron accepting moieties imparted the nonlinear optical properties to the chromophores. The electron rich carbazole core served as a template towards either one-dimensional or two-dimensional chromophores. This structural difference, together with the different lengths for the alkyl chains on the quaternary nitrogens, is expected to result in specificity. More efficient acceptor groups (pyridinium, benzazolium, benzothiazolium) on the carbazole donor core resulted in improved second- and third-order nonlinear optical properties. Selectivity and efficiency for combined second-harmonic and two-photon excited fluorescence based microscopy imaging are demonstrated by simultaneous imaging of specific targets in a multimodal multiphoton microscope.

Keywords: carbazole, nonlinear microscopy, two-photon fluorescence, secondharmonic generation.

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