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Molecular Motion and Performance Enhancement of BORAZAN Fluorescent Dyes
Author(s) -
Morin Tyler J.,
Lindeman Sergey V.,
Gardinier James R.
Publication year - 2009
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200800806
Subject(s) - chemistry , substituent , aniline , intramolecular force , moiety , amination , photochemistry , fluorescence , ligand (biochemistry) , spectroscopy , chromophore , medicinal chemistry , crystallography , stereochemistry , catalysis , organic chemistry , biochemistry , physics , receptor , quantum mechanics
Abstract The preparation of three 2,6‐dipyrazolyl‐4‐X‐anilines, H(pz 2 An X ) (X = p ‐CF 3 , Cl, t Bu) using CuI‐catalyzed amination is described. Subsequent reactions of H(pz 2 An X ) with triphenylboron proceeds with benzene elimination to give the corresponding Ph 2 B(pz 2 An X ) compounds in high yields. The Ph 2 B(pz 2 An X ) are more highly emissive in the solid state than the previously reported BORAZAN fluorophores, Ph 2 B(pzAn X ), their monopyrazolyl counterparts. As with the Ph 2 B(pzAn X ), the color of emission in Ph 2 B(pz 2 An X ) can be tuned simply by varying the para ‐aniline substituent where the emission of Ph 2 B(pz 2 An X ) is red‐shifted relative to the corresponding Ph 2 B(pzAn X ) derivatives. The electronic properties were studied by cyclic voltammetry and electronic absorption/emission spectroscopy as well as by density functional calculations (B3LYP/6‐31G*). The di‐pyrazolyl derivatives exhibit greater stability toward solvolysis and higher photoluminescent quantum yields (despite the red‐shift in emission) compared to their monopyrazolyl counterparts presumably due to kinetic stabilization of the chromophore imparted by the second pyrazolyl ligand. For Ph 2 B(pz 2 An X ), evidence for intramolecular motion of the diphenylboryl moiety traversing both pyrazolyl groups was detected by variable temperature 1 H NMR spectroscopy. The rate increases with increasing electron‐donor abilities of the para ‐aniline substituent.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)