The present study details a metal- and solvent-free synthesis of 11H-pyrido[2,1-b]quinazolin-11-one (1) and its photophysical properties as an acid or base-sensitive sensor. The absorption spectra in organic solvents revealed a small blue shift on passing from nonpolar to polar solvents, but when measured in buffered aqueous solutions the spectra were observed to be pH-dependent. Additionally, the emission spectra recorded in different organic solvents revealed only minor differences between the solvents and a moderate fluorescence quantum yield. However, the emission spectrum of 1 revealed a pH-dependent behavior. At pH 7 the emission spectrum was similar to that in acetonitrile, whereas at pH 1 the emission intensity skyrocketed, whilst at pH 14 fluorescence was switched off. The emission from 1 was reversibly switched on and off by control of the pH. The adsorption of 1 on silica disks provided a simple means for sensing gas-phase acids or basic amines. Exposure of the disks to AcOH, HCl, or TFA vapors revealed an acid-dependent increase of the emission spectrum intensity area. Disks exposed to acid vapors (switch on fluorescence) were readily recycled by exposure to ammonia or other volatile amines (switch off fluorescence). The modified silica disks could be cyclically switched on and off multiple times without significant change to the signal efficiency. NMR spectroscopy and TD-DFT calculations were used to investigate the dramatic changes to the photophysical properties of 1 as a consequence of the pH-dependent behavior.

本研究详细介绍了 11 H -pyrido[2,1 - b ]quinazolin-11-one ( 1 )的无金属和无溶剂合成及其作为酸或碱敏感传感器的光物理特性。有机溶剂中的吸收光谱显示出从非极性溶剂到极性溶剂的小蓝移，但在缓冲水溶液中测量时，观察到光谱与 pH 值有关。此外，在不同有机溶剂中记录的发射光谱仅显示溶剂之间的微小差异和中等荧光量子产率。然而，发射光谱1揭示了 pH 依赖性行为。在 pH 7 时，发射光谱类似于乙腈，而在 pH 1 时，发射强度猛增，而在 pH 14 时，荧光被关闭。通过控制 pH 值可逆地打开和关闭1的发射。吸附量1二氧化硅圆盘上的 提供了一种检测气相酸或碱性胺的简单方法。将圆盘暴露于 AcOH、HCl 或 TFA 蒸气显示发射光谱强度区域随酸增加。暴露于酸蒸气（开启荧光）的圆盘通过暴露于氨或其他挥发性胺（关闭荧光）而易于回收。修改后的二氧化硅盘可以循环打开和关闭多次，而不会显着改变信号效率。核磁共振光谱和 TD-DFT 计算用于研究1的光物理性质由于 pH 依赖性行为而发生的巨大变化。