Solid State Chemistry Of Emodin And Chelerythrine

The physicochemical properties of a material depend not only on its chemical structure,but also packing patterns in the crystal lattices.A compound can exist in many solid forms,such as polymorphs,solvates,cocrystals,salts and amorphous etc.Conformations and packing patterns of a molecule in various solid forms can affect its physicochemical properties,such as melting point,mechanical behavior,optical property and solubility etc.Thus,we can modulate the physicochemical properties of a specific compound via controlling the conformations or packing patterns in its solid states.Crystal engineering has exhibited significant academic and practical values on material science,pharmaceutics,and other fields.In this study,the solid state chemistry(including polymorphs,solvates,cocrystals and salts)of emodin(EM)and chelerythrine(CHE)were carried out.Both EM and CHE are natural occurring dyes and widely applied in traditional Chinese medicines(TCM).In the research of emodin,three new polymorphs,two hydrates and six solvates were discovered.The fluorescent properties of these solid forms were investigated.The phase transformation relationships among these solid forms were fully studied.A new strategy to find mechanochromic luminescent materials from natural occurred dyes without burdensome chemical modification processes was proposed.The mechanochromism and vapochromism phenomena during the solid-state transformation processes of EM presented the potential applications in force,organic vapor sensor and reversible writing.On the basis of their single crystal structures,frontier orbital calculations were conducted to analyze fluorescent color differences among these solid forms.In addition,fine tuning the colors of natural pigment EM with superior stability were realized through cocrystal engineering.As for CHE(hydrochloride commercially available)with ionic center,salt profiling was conducted.The hydrosulfate as well as the mesylate of CHE were obtained in attempt to develop multi-stimuli response materials based on the unique transformation processes of each salt.In chapter 1,the development of crystal engineering and stimulus response materials were introduced.The concept,preparation methods and characterizations of polymorphs,solvates,cocrystals and salts were described.The influences of solid states on physicochemical properties were emphasized.In chapter 2,the mechaochromic phenomenon of natural occurred pigment was uncovered.In this section,a new strategy was put forward to develop stimulusresponse fluorescent materials from natural occurred dyes for the first time and emodin was taken as an example to study the differences on fluorescent property among different solid forms.Three new polymorphs(form I-III),two hydrates(hemihydrate HH and dehydrate DH)were discovered.Except for form III,the single crystals of other polymorphs and hydrates were obtained,and their crystal structures were resolved by single crystal X-ray diffraction(SCXRD).Comprehensive solid-state characterizations including X-ray powder diffraction(XRPD),morphology analysis,solid-state fluorescent spectra(SFS),thermal analysis,vibration spectrum and dynamic vapor sorption(DVS)were carried out.Since EM is a TCM,powder dissolution test was conducted.The “spring and parachute” in the powder dissolution diagrams were caused by the rapid transformation from polymorphs and hydrates to monohydrate.This phenomenon indicated that polymorphs have limited advantages in improving the solubility of EM.However,these solid forms exhibited obvious differences in fluorescent color.Phase transformation relationships among these solid forms were fully studied via VT-XRPD,hyper-DSC,and hot stage microscopy.Form I is the stable form,while form II and form III are the metastable form under room temperature.Form II and form III could transform to form I at high temperatures.HH and form II are isomorphs.As for the desolvation process of HH,it first changed to form II after dehydration,and then transformed to form I with further heating;while DH changed to form III after dehydration,and then transformed to form I upon heating.The fluorescent color changes during the above-mentioned phase transformation processes were investigated.Reversible fluorescent color changes could be observedin the force triggered reversible transformation process between form I and amorphous.This result provided a demonstration of potential applications for EM as mechanosensor and security ink materials.In chapter 3,the reversible vapochromic phenomenon among EM solvates were discovered.In order to find another reversible transformation process with a larger maximum emission wavelength difference,further researches on the solid-state chemistry of EM were carried out.Another six EM solvates,namely S1(methanol),S2(ethanol),S3(Acetone),S4(Acetonitrile),S5(chloroform)and S6(1,4-diaxone),were discovered.Their single crystals were all obtained and their structures were determined by SCXRD.Thermal analysis as well as SFS characterization were conducted.The reversible vapochromic phenomena among EM solvates were discovered and their potential application on organic vapor sensing was explored.Moreover,the reversible transformation process(S2 to S4)with the largest maximum emission wavelength was taken to study the potential application of EM as a security ink material.To get further insight into the differences of EM solvates in their fluorescent properties,single crystal analysis and density functional theory(DFT)calculation were conducted.The results showed that not only ?-? interactions but hydrogen bond patterns can affect the maximum emission wavelength.The energy gaps between HOMO and LUMO orbitals of EM solvates are in accordance with the tendency of their fluorescent maximum emission wavelengths.In chapter 4,cocrystal engineering strategy was applied to realize fine color modulation of natural pigment EM with superior stability.With the aim of diversifying hues and improving color stability of natural dyes and pigments,cocrystals of EM were designed through pyridine-phenol,amide-phenol and carboxyl-phenol synthons and coformers with similar chemical structures were chosen.Slow evaporation method was applied.Seven cocrystals of EM including 2EM-BPD,EM-BZA,EM-PCA,EM-2NIA,2EM-NIA,EM-PMA form I and EM-PMA form II as well as their single crystals were discovered.Physicochemical properties especially optic properties were systematically characterized for these seven cocrystals.A “yellow-orange-dark red” fine color gradient could be observed.Their single crystal structure analyses revealed that pyridine-phenol and amide-phenol synthons existed in EM cocrystals.The hydrogen bond interactions as well as intermolecular charge transfers helped to modify the conjugation of chromophore and the HOMO-LUMO energy band gap so as to realize fine tuning the color of EM.Furthermore,the color stability of EM cocrystals were investigated.EM-PMA form I and form II presented better color stability in the accerlerated stability test(40oC 75% RH)than EM itself.In chapter 5,salt profiling was used as a new strategy to modulate the stimulusresponse types for fluorescent materials.Few materials could response to several stimulus types simultaneously,which is mainly due to the limited number of reversible transformation processes for a specific compound.Thus,we tended to use salt transformation as a convenient method to modulate the stimulus-response types of fluorescent materials.In this study,we took natural occurred fluorescent molecule CHE as an example.The hydrosulfate and mesylate of CHE were obtained by the salt screening process of CHE hydrochloride.Hydrochromic phenomenon can be recognized after a careful study of CHE-Cl.It was uncovered that mechanical and thermo stimuli can trigger fluorescent color changes in CHE-HSO4 and CHE-MSA,respectively.In this way,the stimulus-response type modulation was realized without complicated chemical modification procedure.