Rhodamine Synthesis

Traditional way of synthesizing sensitive rhodamine starts with rhodamine B, amino compound, and some alkali additive in the presence of weak base. However, for RH-PY, the stearic hindrance of pyrene slows the reactivity, and the reaction does not go to completion. Therefore, the reaction procedure was modified as follows. First, HATU and DIPEA were used to activate the carboxyl group of rhodamine B, then the activated rhodamine B was reacted with 1-aminopyrene. By introducing this method, the reaction completed, affording the target product in high yield (70%). The structure of RH-PY was analyzed by 1H-NMR and ESI-TOF. Figure S1 shows the 1H-NMR spectrum of RH-PY. Interestingly, there are two series of peaks (a, a′ and b, b′), characteristics
It is highly sensitive to acid in the solution sate, enabling its wide application as pH-dependent probes. In acidic solutions, the ring-opened form is predominant, and therefore it is strongly fluorescent. Although this acid-sensitive equilibrium has been well known in solutions, its properties in the solid states are not well examined. Therefore, relative test of acid gas-sensitive property of RH-PY was proposed in this study. Figure 1. (A) Device schematic of acid-gas sensitive test, (B) Absorption variation of RH-PY under the stimuli of acid gas.

Figure 1(A) shows the device for the acid-gas sensitive test. The bottle held concentrated HNO3 acid up to its 1/3 volume. The sample was cast on a glass and then set on the bottleneck to fully cover the sample. Concentrated HNO3 is a volatile acid, and liquid HNO3 can easily vaporize. As expected, RH-PY is highly sensitive to gaseous HNO3. As shown in Figure 1(B), the absorption of initial sample is centered at 350 nm. Upon exposure to fuming concentrated HNO3 vapor, a new peak centered at 570 nm began to appear. This peak is assigned to the open-form of RH-PY, demonstrating that the ring-opening occurred upon the stimulation of gaseous HNO3. The acid gas response of RH-PY was accomplished in 5 min, and such short time further shows the advantage of RH-PY in the application of acid gas sensitive
Utilizing light as external stimulation has numerous advantages, as light-triggered intelligent materials response fast to the external stimulations and produce no by-products or contaminations during the response time under light exposure. Rhodamine is a class of dyes with long-wavelength absorption and emission, high absorption coefficient and quantum efficiency, and good photostability. However, because of the extreme short lifetime of its ring-open state, the photochromic rhodamine is rarely