Syntheses And Properties Of Near-infrared BODIPY Derivatives

In the past two decades,the design and synthesis of boron-dipyrromethene(BODIPY)dyes have received increasing attention owing to their wide applications in diverse research fields,especially as biological labels,fluorescent sensors,photodynamic therapy,organic solar cells and organic light-emitting diodes.This has been related to their excellent properties such as large molar extinction coefficients,high fluorescence quantum yields,structural versatility and high stability toward postmodification.However,their absorption and emission wavelengths tipically range between 470 and 530 nm,which limits some of their applications in biological and material science that generally require dyes absorb and emit at longer wavelengths in the far-red or near-infrared(NIR)region.Therefore,the development of new NIR BODIPY dyes has been a research hotspot in recent years.This thesis puts forward its own suggestions and practical results for how to construct NIR BODIPY dyes with excellent spectroscopic properties and chemical stability.1.Introducing the papa-benzoquinone moieties at the BODIPY core to reduce the LUMO level of the entire molecule.A NIR absorbing BODIPY dye 2-O coupled with two benzoquinone moieties at its 3,5-positions was synthesized for the first time.The Knoevenagel condensation reaction was used to prepare BODIPY dye 2-OH,and followed by oxidization with Ag2O to obtain BODIPY dye 2-O.In dichloromethane,the UV-vis-NIR absorption spectrum of 2-O exhibits two major bands at 795 and 895 nm in the NIR region,while 2-OH shows maximum absorbance at 661 nm and strong fluorescence at 692 nm(?F=0.59).Compound 2-O exhibits excellent chemical and electrochemical redox properties.Compared with 2-OH,the frst reduction potential of 2-O is anodically shifted for 710 mV,whereas the first oxidation potential is close,indicating that the LUMO energy level and the HUMO-LUMO energy gap of 2-O are lower than those of 2-OH,resulting in a dramatic bathochromic shift of the S0-S1 transition of 2-O.2.Introducing benzimidazolyl at the meso-position of BODIPY core,and followed by post-modification.2-The first examples of meso-(2-benzimidazolyl)BODIPY derivatives 3a-c and 4a were designed,synthesized and characterized.In toluene,the absorption and fluorescence emission bands of compound 3a appear at 533 and 578 nm,respectively.The fluorescence quantum yield is up to 0.45,which is much higher than those of previously reported meso-heterocyclic BODIPYs.It is likely that the dual constraints caused by the two intramolecular hydrogen bonds limit the rotation of the benzimidazolyl ring,thereby a decreasing incidence of nonradiative decay.In addition,the distyryl coupled BODIPY 4a shows maximum absorbance at 676 nm and fluorescence at 712 nm and maintains ?F value over 0.3 both in nonpolar and polar solvents.meso-(2-Benzimidazolyl)BODIPY can be used as a platform and then modify it to achieve novel NIR BODIPY dyes.