# Synthesis and Application in Cell Imaging of
## 4 Discussion  
In this study, we synthesized the biocompatible acridone derivatives, comprising an electron acceptor vinyl pyridinium and an electron donor acridone. Acridone is known as a biocompatible and media-sensitive chromophore, the scaffold of which could easily be combined with other functional groups to form unique biomarkers. In order to increase the optical diversity, the acridone core was conjugated with vinylpyridine groups on the 2,7-positions to form a donor-acceptor chromophore, leading to the twisted intramolecular charge transfer (TICT) property. Furthermore, a dodecyl group was incorporated into the N10 position, named MeAcd12C, which serves specific targeting ability for  
Figure 6: Normalized absorption and fluorescence emission spectra of fluorogens from MeAcd12C (**a,b**) and MeAcd12P (**c,d**). Compounds were dissolved in 0%, 25%, 50%, 75%, and 100% of H\({}_{2}\)O mixing ratios with THF (_v/v_). The corresponding excitation wavelengths were determined from the absorption maxima present in each absorbance spectrum. cell imaging. We also replaced the dodecyl group with N-dodecyl-N-methyl-piperidinium to obtain MeAcd12P, which was further characterized to reveal its physicochemical properties and was subjected to different applications. By considering acridone as a major electron donor in this study, we synthesized MeAcd12C and MedAcd12P decorated with the distinct electron acceptors. Although two absorption peaks from MeAcd12C, MedAcd12P, and acridone could be observed, the basic optical spectra of MeAcd12C and MedAcd12P were significantly affected by the solvent polarity [29]. From the optical properties as observed in our study, we suggested that the optical diversities could be due to the incorporated vinyl pyridinium and dodecyl pyridinium, respectively, which were employed as electron acceptors. The major absorption peaks from the two compounds located at 450 nm might originate from the acridone core. Although there were three absorption peaks from MeAcd12C and MedAcd12P in EA, no emission peaks from these compounds could be observed. A hypochromic shift was observed with increasing solvent polarity. It is important to note that the fluorescence intensities from MeAcd12C and MedAcd12P were observed to be relatively lower in magnitude while in H\({}_{2}\)O than in any other protein organic solvent. This suggests that the two acridone derivatives possess selective fluorescence depending on the environment, which proved to be advantageous in cell imaging. We observed that the quantum yields of the two compounds were independent of solvent polarity. The two compounds exhibited high quantum yields in polar protic organic solvents, such as MeOH and EtOH, and displayed yellow fluorescence. Polar aprotic solvents such as DMSO, MeCN, Ace, and DMF resulted in a red-shifted fluorescent emission. However, very low quantum yields were obtained in H\({}_{2}\)O, THF, and DCM. The selective photoluminescence abilities of MeAcd12C and MedAcd12P could be exploited as potential biomarkers in cell imaging. Acridone has been extensively studied in the induction of cell apoptosis and in the development of chemotherapeutic agents [30; 31]. Treatment with acridone inhibits the ATP-binding cassette subfamily G member 2 protein to improve the multidrug resistance in breast cancer therapy [32; 33]. In order to evaluate the biocompatibility of MeAcd12C and MedAcd12P, we studied their cytotoxicity behavior in the nontumorigenic H184B5F5/M10 and cancerous HeLa cell lines at various concentrations. The EC50 value of MeAcd12P was approximately at 1.0 \(\upmu\)M for HeLa cells and in the range of 10-30 \(\upmu\)M for H184B5F5/M10 cells. Both MeAcd12C and MedAcd12P showed selective cell toxicity for H184B5F5/M10 and HeLa cells, thus implying that the acridone scaffold derivatives are potential candidates in cancer therapy. We aim to further investigate the intrinsic cytotoxicity effects in other cell lines to understand the underlying mechanisms.