Halogen Bonding Supramolecular Architecture And Fluorescent Molecule Switch Behavior

Chapter 1 Halogen bonding is the noncovalent interaction between halogen atoms(Lewis acids) and neutral or anionic Lewis bases.History,current situation and main features of the interaction were given,and the close similarity with the hydrogen bonding became apparent.Some heuristic principles are presented to develop a rational crystal engineering based on halogen bonding.The focus was on halogen-bonded supramolecular architect- tures given by halocarbons.The potential of the interaction was shown by useful applications in the field of synthetic chemistry,material science,chemical sensing and molecular recognition,bioorganic chemistry.Chapter 2 The data about geometries and interaction energies for the carbon tetrabromide complexes with methanol,ethanol,dioxane,dietyl ether, tetrahydrofuran using ab initio methods were obtained.C-Br…O distances are within the van der Waals radius sum,which revealed the existence of the weak halogen bonding interaction between Bromine and Oxygen atoms.The photoelectrical characters of carbon tetrabromide(CBr₄) dissolved in methanol,ethanol,acetone,dioxane,dietyl ether,tetrahydrofuran were investigated.High concentration-dependent halogen bonding(XB) specific solvent effect co-existed with the highest concentration general solvent effect when concentration of CBr₄ was over 7.8×10^-3M～1.6×10^-2M critical concentration range,in contrary,below this concentration range only did general solvent effect occur.Charge-transfer(CT) interaction between halogen bonding donor-acceptor resulted in spectral red-shift as hydrogen bonding (HB).Among these,UV-Vis spectrum of specific solvent effect was resolved easily in acetone,as for other five solvents,only could by spectral digital subtractions of the critical concentration absorption of CBr₄ from the spectra of solutions containing both reagents obtain the distinct spectra of specific solvent effect due to the spectra overlaping between the highest concentration general solvent effect and specific one.1:1 complexes formed were testified by modified Benesi - Hildebrand equation.The linear correlation of anodic potentials with the spectral energies of four organic solvents complexes established the high concentration-dependent charge-transfer character of the CBr₄/solvent associations.Ambient light made CBr₄ disassociate bromine which lead to spectral tail in the range of 350～390nm.Chapter 3 In this chapter the intermolecular crystals self-aggregated by DPY/5-Isal and Py /DIF₄B were obtained,respectively.The results from single crystal diffraction indicated:The former was ladder-like crystal with the feature of both bilateral "ladder columns" constructed by the C-I…O (carbonyl) halogen-bonding from 5-Isal molecules and "ladder girder" did by hydroxide from carboxylic group and nitrogen from 4,4-Bipyridyl.The latter was "sandwiched column-like" infinite chain containing two DIF₄B molecules with reverse iodine between two Py molecules,Ï€-Ï€stacking drove the self-aggregation of Py and DIF₄B molecules,but the two neighboring columns were connected by I…I interaction.Synergetically interaction by halogen-bonding with hydrogen-bonding,Ï€-Ï€stacking and other weak interactions had great meaning for the understanding for life initiation, medical design and intermolecular recognition in biological bodies.Chapter 4 With decrease ofpH from 7.20 to-1.0,the UV-Vis absorption and fluorescent spectra of the 1,2-bis(4-pyridyl) ethylene(BPE) took on same changing trends at four different successive pH stages:8.45～7.20,7.20～5.62, 5.62～2.60,2.60～-1.0,namely corresponding to no change,decrease,increase, decrease again.Among these,at the range of 7.20～5.62,the wavelength of fluorescence blueshifted from 418nm to 359nm,but that of UV-Vis,in contrast,redshifted from 285nm to 298nm.Fluorescence had a drop even to quench upon pH from 2.60 to -1.0 due to its cation-Ï€interaction to reduceÏ€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 spectra indicated that BPE had "off-on-off' fluorescence emission behavior.The spectra of BPE were nearly independent on the presence ofαandβ-cyclodextrins.