With the decrease of pH value from 8.45 to -1.0, the UV-Vis absorption and fluorescent spectra of 1,2-bis（4-pyridyl） ethylene（BPE） took on the same changing trend at four different successive pH stages： 8.45--7.20, 7.20--5.62, 5.62--2.60, and 2.60--1.0, namely, no change, decrease, increase, and decrease again. Among these, in a range of 7.20--5.62, the fluorescence wavelength blueshifted from 418 to 359 nm, but the UV-Vis absorption wavelength, in contrast, redshifted from 285 to 298 nm. The fluorescence intensity of BPE had a drop even to quench upon a decline in the pH value from 2.60 to -1.0 probably owing to its cation-re interaction to reduce the π electron cloud density of BPE. Two dissociation constants, pKa1（4.30±0.01） and PKa2（5.65±0.04）, were obtained based on fluorescence data. The changes of fluorescence spectra indicate that BPE has ＂oft-on-off＂ switch behavior. The fluorescent spectra of BPE were nearly independent on the presence of α- and β-cyclodextrins.
The theoretical calculation and spectroscopic experiments indicate a kind of triangular three bonding supramolecular complexes CBr4…X^-…-H-C, which consist of carbon tetrabromide, halide, and protic solvent molecule （referring to dichloromethane, chloroform and acetonitrile）, can be formed in solution. The strength of halogen and hydrogen bonds in the triangular complexes using halide as common acceptor obeys the order of iodide〉bromide〉chloride. The halogen and hydrogen bonds work weak-cooperatively. Charge transfer bands of halogen bonding complexes between CBra and halide are observed in UV-Vis absorption spectroscopy in three solvents, and then the stoichiometry of 1：1, formation constants K and molar extinction coefficients ε of the halogen bonding complexes are obtained by Benesi-Hildebrand method. The K and ε show a dependence on the solvent dielectric constant and, on the whole, obey an order of iodide〉bromide〉chloride in the same solvents. Furthermore, the C-H vibrational frequencies of solvent molecules vary obviously with the addition of halide, which indicates the C-H…X- interaction. The experimental data indicate that the halogen bond and hydrogen bond coexist by sharing a common halide acceptor as predicted by calculation.
