The Development And Application Of A New Type Of Rhodamine Derivatives

Rhodamine is widely used as laser dye and fluorescent labels due to its excellent photostability and photophysical property. The rhodamine derivatives were also applied into molecular switch and flurescent probes. For example, in the field of fluorescent probe, rhodamines have been developed in the detection of a series of guest molecules, however, there’s a lot of guest molecule to be determined for us. Common cations, such as Mg²⁺, Co²⁺, Ni²⁺, remain to be a challenge for rhodamine derivatives. Traditional modification strategies concentrate on spirolactam, although this type of rhodamine was fully developed, only several ions could be detected, Thus, we must think “outside of the box”, and develop new strategies.Most people believed the 3 prime position on rhodamine is sterically hindered, it’s hard to modify this position and it makes no sense. However, this paper will concentrate on the modification of 3’ position. We consider this position is orth to the carboxyl group, this position will have a great impact on rhodamine. If combine with traditional modification strategies, it will greatly affect the performance of trational rhodamine. Based on these strategies, the paper will demonstrate the following contents:1. This paper explored the synthesis route of this type of rhodamine. According to patents, we explored many experiments, and successfully synthesized this new type rhodamines in low budget. To our pleasure, we nearly get the isomers on 6’ position, we got pure 3’ position modified rhodamine, and successfully got the single crystal structure of Rha-amino（amino group on the 3’ position of rhodamine B）. Compared with traditional rhodamines with modification on 4’ and 5’, which are hard to purify, this type of rhodamine is easy to purify, which is of great benefit to commercial application. Besides, contracting to rhodamine B, this type of rhodamine prefers lactone form when the water content is little, while rhodamine B exists in zwitterionic form.2. Based on the structure of this type of rhodamine, we developed a prototype probe Rha-py, which is a new type of Ni²⁺ sensor based on rhodamine. Because this type of amino-rhodamine could exited in lactone form partially in water phase, and with the polarity of solvent, the content of lactone form will increase until reach a totally lactone. Interestingly, the lactone form is much more reactive than spirolactam, the bond of lactone is easy to be broken. So this type of probe will show fast responsive speed than traditional rhodamine probe. Such as Rha-py, in CH3CN-HEPES buffer solution, the probe could respond to Ni²⁺ immediately and discriminate Cu²⁺, and other cations show no interference, and the whole process is in neutral condition. This probe could detect Ni²⁺ with naked eye, when Ni²⁺ was added to this colorless solution, it will turned into pink color immediately. To our great knowledge, it was the first probe based on rhodamine that could detect Ni²⁺ with high sensitivity and selectivity.3. Based on Rha-amino, we first got rhodamine with hydrazine modified on the carboxyl phenyl ring. We reacted it with hydrazine hydrate in ethanol, and got the probe RhJXJ. This probe could detect Hg²⁺ with high sensitivity and selectivity, and Cu²⁺ won’t have impact on the detection, which is different from traditional spirolactam type rhodamine probe. RhJXJ have no sulfur atom and the structure is simple. The detection limit of the probe was in nanomole level, and it was successfully applied into cell imaging, which implied this probe could be well applied.