Small molecules based Benzothiazole-pyridinium salts with different anions: Two-photon fluorescence regulation and difference in cell imaging application

A series of benzoxazole-pyridinium salt derivatives with two-photon excited fluorescence performance were synthesized and fully characterized. Among them, compounds 2 , 3 and 4 were the isomers with different positions of pyridine N, while compounds 4N , 4S , 4P , 4F and 4B were derived from compound 4 through anion exchanging reaction. Their photophysical properties had been systematically investigated, and the results indicated that the position of pyridine N and the type of anions had a significant influence on their optical properties and bio-imaging application. Transforming the position of pyridine N could affect their fluorescence quantum obviously; the maximum fluorescence quantum is 0.21 for compound 3 in DMF . Meanwhile, we found that the altering anions might be used to regulate their two-photon fluorescence performance, only compounds 4N , 4P and 4B possessed excellent two-photon excited fluorescence emissions , and the highest two-photon cross-section was 1868.69 GM for compound 4B in DMF. In addition, two-photon fluorescence cell imaging experiment demonstrated the potential bio-application of partial compounds with good photostability and low cytotoxicity. A series of water solubility of benzoxazole-pyridium salt derivatives including compounds 2 , 3 , 4 , 4N , 4F , 4P , 4S and 4B with excellent two-photon excited fluorescence performance were synthesized and applied in biological imaging. The structure-property relationship study showed that the position of pyridine N and the type of anions have a significant influence on their optical properties and bio-imaging application. •The structure of target compounds was determined by HR MS with positive and negative ion model. •Counter anions had a influence on the two-photon excited fluorescence emissions. •The position isomerization of pyridine N affected their biological imaging performance.