This investigation focuses on dyes that differ only in the nitro substituent. The NO₂ group leads to a strong hardening of the fluorescence at 298 K. In methylene green (MG) the excitation energy migrates to the system of triplet states. This non-radiative process causes the MG fuorescence absent or too low compared to methylene blue (MB). Moreover, laser-induced fluorescence is completely absent for MG in the investigated solvents. However, at liquid nitrogen temperature, we recorded fluorescence for MG in ethanol 250 times higher than at room temperature and phosphorescence too. The intensity of the MB fluorescence band in ethanol at 77 K is 6 times higher than at room temperature. According to the results of this study, the lifetime in the excited state decreases in the following order: isopropanol > acetonitrile≈ethanol≈dimethyl sulfoxide > > water for MG and chloroform > acetonitrile≈ethanol≈dimethyl sulfoxide > > water≈isopropanol for MB. In addition, MG has phosphorescence in ethanol at 780 nm (12,800 cm⁻¹) and in chloroform at 810 nm (12,300 cm⁻¹).

本研究的重点是仅硝基取代基不同的染料。₂号基团导致荧光在 298 K 处强烈硬化。在亚甲基绿 (MG) 中，激发能迁移到三重态系统。这种非辐射过程导致 MG 荧光缺失或与亚甲蓝 (MB) 相比太低。此外，在所研究的溶剂中，MG 完全不存在激光诱导荧光。然而，在液氮温度下，我们记录了 MG 在乙醇中的荧光比室温高 250 倍，并且也记录了磷光。77 K 乙醇中 MB 荧光带的强度比室温高 6 倍。根据这项研究的结果，激发态下的寿命按以下顺序降低：异丙醇 > 乙腈≈乙醇≈二甲基亚砜 > > MG 和氯仿的水 > 乙腈≈乙醇≈二甲基亚砜 > > 对于 MB，水≈异丙醇。此外，MG 在乙醇中具有 780 nm（12,800 cm^-1 ) 和在 810 nm (12,300 cm ^-1 ) 的氯仿中。