Driving the Emission Towards Blue by Controlling the HOMO‐LUMO Energy Gap in BF₂‐Functionalized 2‐(Imidazo[1,5‐a]pyridin‐3‐yl)phenols

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 ( 1 H, 13 C, 11 B, 19 F 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 ( 1 ILT), 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 σ p Hammett constant.

Long-Alkyl Chain Functionalized Imidazo[1,5-a]pyridine Derivatives as Blue Emissive Dyes

“…Analysis of the lifetime decay curve and determination of absolute quantum yields were done using Fluoracle ® Software package (Version 1.9.1) which runs the FS5 instrument. C1 and C1-BF 2 have been synthesized using an already reported method [41]. All procedures have been done under inert atmosphere following the conventional Schlenk's technique.…”

“…Ligands CX displayed a weak fluorescence and were not thoroughly investigated, while all the boron compounds showed blue fluorescence emission in solution (Figure 2). C1 and C1-BF 2 have been studied previously [41] and are used here as a comparison for the luminescence properties of the novel compounds.…”

“…Ligands CX displayed a weak fluorescence and were not thoroughly investigated, while all the boron compounds showed blue fluorescence emission in solution (Figure 2). C1 and C1-BF2 have been studied previously [41] and are used here as a comparison for the luminescence properties of the novel compounds. Firstly, in order to evaluate a possible solvent effect, we started the evaluation of the photophysical properties of this series of compounds from measuring the fluorescence parameters of C3-BF2, taken as a representative example of the series, in different solvents (Table 1) (Figures S21-S23).…”

“…In our continuing research on coordination compounds with nitrogen ligands [27][28][29][30], we recently focused our attention on imidazo [1,5-a]pyridine scaffolds [31,32], utilized both as N,N- [33][34][35] or N,O- [36][37][38][39] bidentate ligands. Specifically, we combined the properties of these heterocycle and BODIPY, mimicking the latter upon the coordination of a BF 2 fragment using N∩O substituted (imidazo[1,5-a]pyridin-3-yl)phenolates [40,41]. These compounds showed excellent fluorescent properties and photostability and they have been used in preliminary tests as emissive materials in the fabrications of some blue emissive OLEDs [42].…”

Effect of Phenolic Substituent Position in Boron Complexes of Imidazo[1,5‐a]pyridine

“…Transient absorption measurement revealed that the intersystem crossing process from the singlet excited state to triplet excited state causes the low fluorescence quantum yield of 2 . Very recently, S. Brenna and co‐workers reported the substituent effect of phenolic group at 3‐position of 1‐methylimidazo[1,5‐ a ]pyridine‐boron complex [7a] . In this manuscript, we describe the synthesis of blue luminescent boron complexes 3 of 3‐( o ‐hydroxyphenyl)imidazo[1,5‐ a ]pyridine (Figure 1b) and the evaluation of their excited state dynamics to elucidate the effect of phenolic substituent position in boron complex of imidazo[1,5‐ a ]pyridine ligand.…”