Synthesis, two-photon absorption properties and bioimaging applications of mono-, di- and hexa-branched pyrimidine derivatives

• The molecular geometry optimization is based on crystal data.
• The photophysical properties of them were systematically investigated.
• The two-photon cross-sections were measured by two-photon excitation fluorescent and Z-scan methods.
• The di- and hexa-branched pyrimidine derivatives exhibit large two-photon cross-section in 800–890 nm regions in DMF solution.
• The potential application of the di-branched chromophores in two-photon biological imaging was evaluated.

A series of mono-, di- and hexa-branched pyrimidine derivatives possessing two-photon absorption have been synthesized. The spectral features of the dyes showed solvatochromic with significant bathochromic shifting of the emission spectra and large Stokes shifts in more polar solvents mainly due to the intramolecular charge-transfer. The two-photon absorption cross-section values were measured by two-photon excited fluorescence and open aperture Z-scan methods. The results revealed that the two-photon absorption cross-section values were enhanced with increasing electron-donating strength of the end group and branch number. The photophysical properties of the dyes were further investigated with the aid of theoretical calculations. In addition, the di-branched dyes has the largest values of two-photon absorption cross-section per molecular weight, low cytotoxicity and can be internalized by human liver cancer cell line and accumulates in the cytoplasm, allowing for live cell two-photon fluorescence imaging, so it is promising for in vitro and vivo cellular imaging applications.