Synthesis, crystal structures, two-photon absorption and biological imaging application of two novel bent-shaped pyrimidine derivatives

• Two novel bent-shaped dyes were confirmed by crystallography.
• The molecular geometry optimization for calculation is from crystal data.
• The photophysical properties of them were systematically investigated.
• The two dyes exhibit strong two-photon absorption in near-infrared range.
• The potential applications in two-photon biological imaging were evaluated.

Two novel bent-shaped D–π–A–π–D chromophore molecules, 2-pyrazolyl-4,6-bis (4-N,N-ethylaminostyryl)pyrimidine (Z1) and 2-imidazolyl-4,6 –bis- (4-N,N- ethylaminostyryl) pyrimidine (Z2), were synthesized and fully characterized. It was found that the both bent-shaped chromophore molecules crystallize in the orthorhombic system, space group of P212121. The photophysical properties and the connections between structure and properties of the chromophores were investigated both experimentally and theoretically. It was revealed that both absorption and single-photon excited fluorescence (SPEF) spectra show remarkable bathochromic shifts with increasing polarity of the solvents. The two chromophores have strong two-photon excited fluorescence and large two-photon absorption cross-sections in the near-infrared range. Additionally, two-photon microscopy (TPM) fluorescent imaging of BEL-7402 cells labeled with the Z1 and Z2 revealed their potential application as a biological fluorescent probe.