Synthesis of naphthyl derived rhodamine dyes, spectral characterization by experimental and DFT methods

Synthesis of rhodamine dyestuffs is important due to their use in various fields. In this study, rhodamine dye derivative 9-[2-(ethoxycarbonyl)phenyl]-N-ethyl-6-(ethylamino)- 2,7-dimethyl-3H-xanthene-3-iminium chloride (Rhodamine 6G) was used by reaction with ethylenediamine. 2-(2-aminoethyl)-3',6'-bis(ethylamino)-2',7'-dimethylspiro(isoindoline1,9'-xanthene)-3-one (Rh-EN), which has been synthesized before in the literature. The starting material was synthesized. Then, as a result of the reactions of Rh-EN compound and three different naphthaldehyde derivative compounds (1-naphthaldehyde, 4-methoxy1-naphthaldehyde and 2,3-dimethoxy-1-naphthaldehyde) under appropriate conditions, new naphthyl-derived rhodamine dyestuffs (SAD-1, SAD-2 and SAD-3) were obtained. All synthesized compounds were purified using the appropriate method and their molecular structures were elucidated using HR-MS, IR, Raman and NMR spectroscopic methods. The theoretical calculations of the synthesized compounds were made using the B3LYP method, which is the Density Functional Theory (DFT) approach, and the 6-31G (d,p) basis set. The most stable optimized structures were obtained by means of conformer analyzes scanning torsion angles by small amounts around flexible bonds of the compounds, their electronic properties (HOMO & LUMO, MEP, global reactivity descriptors) were calculated and vibration spectroscopic analyzes were carried out with the help of Potential Energy Distributions (PED). Calculated vibration spectroscopic data were compared with the experimental values, the correlation graphs were drawn, and their compatibility with each other was demonstrated by calculating the correlation coefficient (R2) values as 0.9999. KeyWords: Rhodamine, naphthaldehyde, DFT, IR, Raman, NMR