Phenylthiophene-dipicolinic acid-based emitters with strong solution blue and solid state green emission
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The synthesis and characterization of highly efficient blue emitting phenyl?thiophene compounds derivatized with dipicolinic acid bis(diethylamide) and dipicolinic acid diethyl ester 1, 2, and 3 are reported. Quantum yields were determined to be between 97% and 76% in methanol and 99% and 49% in toluene solution. The solvent dependences of the solution luminescence behavior are discussed in terms of solvent refractive index and dielectric constant as well as hydrogen-bonding capability. Luminescence is also observed in the solid state for the three compounds. A bathochromic shift in the emission wavelength is accompanied by solid-state quantum yields between 29% and 4%. HOMO and LUMO energies, in the range ?5.55 to ?5.71 eV and ?2.20 to ?2.48 eV, respectively, were determined experimentally from cyclic voltammetry and absorption spectroscopy experiments. The electrochemical characterization revealed that cyclic voltammetry can be utilized to deposit thin films of 3. An X-ray quality single crystal of 1 was isolated. This compound crystallizes in the monoclinic space group P21/c with cell parameters a = 15.224(3) �, b = 8.9383(18) �, c = 17.234(3) �, ? =114.36(3)�, and V = 2136.4(7) � Appreciable solid state interactions in the form of ??? or S?S short contacts are not present, only weaker C?H贩�. A large torsion angle of 30.28� between the phenyl and thiophene moieties and a small torsion angle of ?3.37� between the pyridine and the thiophene moieties are seen.