[Theoretical studies on the structure, thermodynamics and spectral properties of rhodamine derivatives modified by amino of central ring].

The structures of three rhodamine derivatives were optimized by means of DFT/B3LYP method, and the data of the structural parameters and thermodynamic parameters of the excited state and ground state of the three rhodamine derivatives and their vibrational spectra and frontier molecular orbital energy level were obtained. On the basis of fully optimized structures of excited state and ground state, their gas absorption and emission spectra were studied by time-dependent density functional theory (TD-DFT), while the effects of their structural features on thermal stability, frontier molecular orbital and spectra properties were fully analyzed. The results indicate that the compound a has the lowest reverse movement degree of terminal amino among these molecules, and in contrast, the compound b was better conjugated and planar, the reverse movement degree of terminal amino improved, the gas absorption and emission spectra were red shifted, and it has the longest maximum emission wavelength and the lowest thermal stability among these molecules. The compound c was best conjugated and planar, its thermal stability and energy of HOMO were the highest, its HOMO-LUMO gap was most narrow, and it has the longest maximum absorption wavelength. It was found that the reverse movement degree of terminal amino of compound c improved compared to b, so its maximum emission wavelength was blue shifted.