| Abstract
| - The reaction between 2-pyrazolyl-4-X-anilines, H(pzAnX), (X = para-OMe (L1), Me (L2), H (L3), Cl(L4), CO2Et (L5), CF3 (L6), CN (L7)) and triphenylboron in boiling toluene affords the respective,highly emissive N,N‘-boron chelate complexes, BPh2(pzAnX) (X = para-OMe (1), Me (2), H (3), Cl (4),CO2Et (5), CF3 (6), CN (7)) in high yield. The structural, electrochemical, and photophysical propertiesof the new boron complexes can be fine-tuned by varying the electron-withdrawing or -donating powerof the para-aniline substituent (delineated by the substituent's Hammett parameter). Those complexeswith electron-withdrawing para-aniline substituents such as CO2Et (5), CF3 (6), and CN (7) have moreplanar chelate rings, more ‘quinoidal' disortion in the aniline rings, greater chemical stability, higheroxidation potentials, and more intense (φF = 0.81 for 7 in toluene), higher-energy (blue) fluorescentemission compared to those with electron-donating substituents. Thus, for 1 the oxidation potential is0.53 V versus Ag/AgCl (compared to 1.12 V for 7), and the emission is tuned to the yellow-green butat an expense in terms of lower quantum yields (φF = 0.07 for 1 in toluene) and increased chemicalreactivity. Density functional calculations (B3LYP/6-31G*) on PM3 energy-minimized structures of theligands and boron complexes reproduced experimentally observed data and trends and provided furtherinsight into the nature of the electronic transitions.
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