A series of benzoylguanidinium salts was prepared and the changes in UV/Vis spectra, triggered by the presence of anions, were investigated. All compounds undergo deprotonation with basic anions like dihydrogenphosphate and acetate in acetonitrile. The most pronounced spectral changes were obtained by deprotonation of N1 -benzoyl-N3 -(p-nitrophenyl) guanidinium chloride which shows the naked-eye visible color change from colorless to yellow. Measured pKa (BH+ ) in acetonitrile ranges from 12-16, which is comparable to the pyridinium cations. The proton transfer equilibria were also tested in acetonitrile/water mixture where all but the most acidic derivatives showed pKa (BH+ ) of 4-6 units which corresponds to apparent association constants of 104 -106  dm3  mol-1 . UV/Vis spectra of neutral and protonated forms were modelled by the TD-DFT approach using CAM-B3LYP and PBE0 functionals and compared to CC2 results. In the case of CAM-B3LYP, a parameter ω, defining amount of long-range exchange correction, was varied to achieve the best agreement with the experimental spectra. The optimized ω parameters are 0.10 a0 -1 for neutral benzoylguanidines and 0.20 a0 -1 for neutral nitrobenzoyl and protonated systems. The larger ω parameter in the latter is ascribed to more pronounced charge transfer character of the HOMO-LUMO transition - the one responsible for the lowest energy absorption band.

中文翻译：

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苯甲酰胍作为阴离子响应系统。

制备了一系列苯甲酰基胍盐，并研究了由阴离子的​​存在引起的UV / Vis光谱变化。所有化合物均与碱性阴离子（如磷酸二氢根和乙腈中的乙酸根）一起去质子化。通过使N1-苯甲酰基-N3-（对硝基苯基）氯化胍去质子化获得最明显的光谱变化，其显示肉眼可见的颜色从无色变为黄色。乙腈中测得的pKa（BH +）为12-16，与吡啶鎓阳离子相当。还在乙腈/水混合物中测试了质子传递平衡，除最酸性衍生物外，所有其他衍生物均显示pKa（BH +）为4-6个单位，这对应于104 -106 dm3 mol-1的表观缔合常数。使用CAM-B3LYP和PBE0功能，通过TD-DFT方法对中性和质子化形式的UV / Vis光谱进行建模，并与CC2结果进行比较。在CAM-B3LYP的情况下，定义了远程交换校正量的参数ω被改变以达到与实验光谱的最佳一致性。对于中性苯甲酰基胍，优化的ω参数为0.10 a0 -1，对于中性硝基苯甲酰基和质子化体系，优化的ω参数为0.20 a0 -1。后者中较大的ω参数归因于HOMO-LUMO跃迁的更显着的电荷转移特性-负责最低能量吸收带的跃迁。为了达到与实验光谱的最佳一致性而进行了各种改动。对于中性苯甲酰基胍，优化的ω参数为0.10 a0 -1，对于中性硝基苯甲酰基和质子化体系，优化的ω参数为0.20 a0 -1。后者中较大的ω参数归因于HOMO-LUMO跃迁的更显着的电荷转移特性-负责最低能量吸收带的跃迁。为了达到与实验光谱的最佳一致性而进行了各种改动。对于中性苯甲酰基胍，优化的ω参数为0.10 a0 -1，对于中性硝基苯甲酰基和质子化体系，优化的ω参数为0.20 a0 -1。后者中较大的ω参数归因于HOMO-LUMO跃迁的更显着的电荷转移特性-负责最低能量吸收带的跃迁。