Modulation of the Photophysical Properties of ß-substituted BODIPY Dyes.

Photophysical properties of BODIPY dyes containing acetyl acetone and benzoyl acetone BF2 unit as an electron accepting substituent at beta position linked via double bond have been investigated using a wide range of solvents of different polarities. The substitution effect at beta position of the BODIPY dyes on their absorption, emission and quantum yield of fluorescence have been the aim of present study. For the synthesized BODIPY dyes fluorescence quantum yields and lifetimes show very sharp decrease with an increase in the solvent polarity, suggesting the involvement of highly polar ICT state de-excitation mechanism along with the local excitation process. The polarity dependent changes in average fluorescence life time and quantum yield values rationalize the formation of ICT states.

Nonlinear Optical Properties of Pyrene Based Fluorescent Hemicurcuminoid and their BF2 Complexes -Spectroscopic and DFT Studies.

The acetyl acetone and benzoyl acetone pyrene based difluoroboron scaffolds and their respective decomplexed congeners were investigated for their nonlinear optical properties in various microenvironment. The geometries of the chromophore were optimized and electronic excitation properties were estimated using time dependant density functional theory. The vertical excitation properties were found to be complimentary to the experimental results. Nolinear optical properties were evaluated using solvatochromism and Density Functional Theory. The experimental nonlinear optical properties well correlated using Mulliken Hush parameters and also compared with calculated values. CAM-B3LYP results were found to be superior over the B3LYP and BHandHLYP methods. The positive solvatochromism in emission were well explained by multilinear regression and bond length alteration.

Solvent-Driven Conformational Exchange for Amide-Linked Bichromophoric BODIPY Derivatives.

The fluorescence lifetime and quantum yield are seen to depend in an unexpected manner on the nature of the solvent for a pair of tripartite molecules composed of two identical boron dipyrromethene (BODIPY) residues attached to a 1,10-phenanthroline core. A key feature of these molecular architectures concerns the presence of an amide linkage that connects the BODIPY dye to the heterocyclic platform. The secondary amide derivative is more sensitive to environmental change than is the corresponding tertiary amide. In general, increasing solvent polarity, as measured by the static dielectric constant, above a critical threshold tends to reduce fluorescence but certain hydrogen bond accepting solvents exhibit anomolous behaviour. Fluorescence quenching is believed to arise from light-induced charge transfer between the two BODIPY dyes, but thermodynamic arguments alone do not explain the experimental findings. Molecular modelling is used to argue that the conformation changes in strongly polar media in such a way as to facilitate improved rates of light-induced charge transfer. These solvent-induced changes, however, differ remarkably for the two types of amide.

Masking and demasking strategies for the BF2-BODIPYs as a tool for BODIPY fluorophores.

An efficient and chemoselective route for transforming BF2-BODIPYs to Et2B-BODIPYs (masking) was developed using Et2AlCl. The Et groups can be easily replaced with F atoms using BF3·Et2O in moist CH2Cl2 to regenerate the BF2-BODIPYs (demasking). The masking-demasking strategy is very useful for synthesizing functionalized BODIPYs via nucleophilic and reductive reactions. The masking strategy was used to synthesize a BODIPY dimer by McMurry coupling of a formyl Et2B-BODIPY, while a new BODIPY with an asymmetrically substituted B-center was synthesized using the demasking strategy.