Design,Syntheses And Properties Of Functional Pyrrolyl Difluoroborates Dyes

Fluorescent boron dipyrromethene?BODIPY?dyes have received increasing research interests because of their excellent optical properties and easy accessibility,and have been widely applied as non-invasive bioimaging,laser dyes,fluorescence labeling agents,sensors,fluorescent switches,photovoltaics/optoelectronics and photosensitizers in the fields of biological medicine and material science.However,the classical BODIPY skeleton generally absorb/emit at around 500 nm.Besides,most BODIPYs have weak fluorescence in the solid state because of?-?stacking,which limits their further applications as optoelectronic devices.The dissertation focuses on overcoming the two problems of most classic BODIPYs with relatively short wavelength or weak fluorescence in the solid states:Firstly,on the modification of BODIPYs with relatively short wavelength,starting from linear modification strategy,we developed a novel method for isoindole BODIPYs.Besides,starting from annular modification strategy,we designed and synthesized a novel family of highly conjugated directly-fused bisBODIPY with locked coplanar conformation through a key FeCl₃-mediated intramolecular oxidative cyclodehydrogenation reaction and its derivatives from the Knoevenagel reaction.Both of the two kinds of BODIPYs absorb/emit in the red to near-infrared region,which are good solutions to the problem of BODIPYs with short wavelength.Secondly,on the weak fluorescence in the solid states,starting from aggregation induced fluorescence engagement?AIE?strategy,we synthesized a series of novel meso-COPyrrole substituted BODIPYs.Besides,starting from designing BODIPY analogues strategy,we designed and synthesized two kinds of novel BF₂ complexes of hydrazine-Schiff-base linked bispyrrole and dipyrrolylquinoxalines.All these dyes we developed above exhibit high fluorescence in the solid states,which well solve the problem of weak fluorescence in the solid states.The dissertation provides a good reference for the further development of efficiently designing and synthesizing novel fluorescent dyes,which mainly contains the following six chapters:1)In Chapter 1,several efficient methodologies for realizing fluorescent BODIPY dyes emitting in red or near infrared or with strong solid fluorescence were introduced and summarized in recent years.2)In Chapter 2,a novel method for isoindole BODIPYs was developed and a series of isoindole BODIPYs containing either symmetrical or unsymmetrical alkyl substitution patterns on pyrrole rings were synthesized and characterized by X-ray diffraction,spectroscopic and electrochemical analysis.Most of these dyes show strong sharp absorption and bright fluorescence emission in the red to near infrared?NIR?region?up to 805 in acetonitrile?.Pyrrolic alkyl substitutions lead to the increase of the HOMO and the LUMO energy levels,and the overall decrease of the energy band gaps of the dye.Solvent-dependent fluorescence emission and life-time decay were observed for those containing 3-methyl substituent on the uncoordinated pyrrole ring,while few varitaion of the fluorescence intensity was observed for the rest of the dyes upon changing the polarity of the solvent.These resultant dyes can be further functionalized via the Knoevenagel condensation on the 3-methyl substituent of the chromophore to install a variety of functionalities.This dimethylamine functionalized isoindole BODIPY shows weak fluorescence at 805 nm in acetonitrile and a ratiometric“turn-on”NIR fluorescence response to the decrease of pH.3)In Chapter 3,a new family of directly-fused bisBODIPY near-infrared fluorescent dyes through a key FeCl₃-mediated intramolecular oxidative cyclodehydrogenation reaction and its derivatives were further synthesized from the Knoevenagel condensation reaction.These dyes display effective expansion of conjugation over the two BODIPYs due to their locked coplanar conformation,showing intriguing electrochemical and spectroscopic properties,such as intensive absorption/emission bands ranging from 676 to 877 nm,relatively high fluorescence quantum yield and high photostability.4)In Chapter 4,a series of novel meso-COPyrrole substituted BODIPYs have been prepared from a simple two-step reaction from easily available dipyrrolyldiketones and prrole derivatives.These dyes exhibit the properties of AIE and strong red fluorescence in the solid states,which is mainly due to their propeller-like structurs that suppress?-?interactions and cause restriction to intramolecular rotation upon aggregation.The packings of these dimmers with hydrogen bondings show no stacking between the adjacent dimmers.These typical J-aggregate type packings of these dyes might explain their good quantum yields in the solid states.5)In Chapter 5,a series of novel BF₂ complexes of hydrazine-Schiff-base linked bispyrrole have been prepared from a simple two-step reaction from commercially available substances,and are high fluorescence in solution,film and solid states comparable or even super to those of their BODIPY analogues with larger stokes-shift and excellent photostabilities.These resultant fluorescent dyes are highly susceptible for the postfunctionalization comparable to that of their BODIPY analogues,as demonstrated in this work via the knoevenagel condensation to introducing functionalities or tether groups to the chromophore.6)In Chapter 6,a set of organic fluorescent dyes of dipyrrolylquinoxalines and their BF₂ complexes were synthesized from commercial reagents,and were characterized by structural,optical,and electrochemical properties.These novel BF₂ complexes showed intensely broad absorption in solution-state in the visible region with absorption maximum centered at visible region up to 583 nm.In comparison with the corresponding ligand,there is an over 110 nm red-shift of the absorption maximum in these BF₂ dyes.Interestingly,all these dyes all exhibit strong solid-state fluorescence with moderate to high fluorescence quantum yields.X-ray structures clearly showed the coplanar structure of quinoxaline with one pyrrole unit and the boron atom of the BF₂ moiety leaving the uncoordinated pyrrole in a nearly orthogonal orientation?the dihedral angle of 70-73°?.This extended conjugation was in a good agreement with the observed red-shift of the spectra.The well-ordered intermolecular packing structures also explained the good solid-state fluorescence properties of these dyes.