Abstract
Several boron compounds with 2‐(imidazo[1,5‐a]pyridin‐3‐yl)phenols, differentiated by the nature of the substituent (R) in the para position of the hydroxy group, have been synthesized and thoroughly characterized both in solution (1H, 13C, 11B, 19F NMR) and in the solid state (X‐ray). All derivatives displayed attractive photophysical properties like very high Stokes shift, high fluorescence quantum yields and a good photostability in solution. Time‐Dependent Density Functional Theory (TD‐DFT) calculations allowed to define the main electronic transitions as intra ligand transitions (1ILT), which was corroborated by the Natural Transition Orbitals (NTOs) shapes. The homo‐lumo energy gap was correlated to the electronic properties of the substituent R on the phenolic ring, as quantified by its σp Hammett constant.
Highlights
In recent years there has been a growing attention towards luminescent compounds suitable for different devices such as Organic Light Emitting Diodes (OLEDs),[1] Light Emitting Electrochemical Cells (LECs),[2] Dye Sensitized Solar Cells (DSSCs)[3] or as fluorescent sensors.[4]
Syntheses and characterization (Imidazo[1,5-a]pyridin-3-yl)phenols RIPP were prepared following published methods,[47] by condensation of 2-acetylpyridine and the corresponding 5-substituted salicylaldehydes, in the presence of ammonium acetate as a source of the imidazolic nitrogen (Scheme 1)
We decided to search for a possible correlation between the electronic properties of RIPP_BF2 compounds and the calculated HOMO, LUMO and LUMO + 1 energies, which are in turn related to the emissive properties
Summary
A series of hydrogenated dyes deriving from this class of molecules has been studied and demonstrated to be efficient blue emissive materials in solution and in thin film.[43] Surprisingly, only few examples of boron derivatives with imidazo-pyridines have been reported in the literature.[44,45] In the recent past, we investigated the previously cited hydrogenated ligands in the synthesis of boron difluoride coordination compounds, which showed excellent optical properties like high fluorescence quantum yields.[46]. The photophysical properties of this class of boron containing compounds are described, focusing especially on the correlation between their electronic properties and their fluorescent behavior
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