Substituted tetraphenylbutadienes as fast scintillator solutes

Abstract

Sixteen previously unknown derivatives of the fast scintillator solute, 1,1,4,4-tetraphenyl-1,3-butadiene (TPB) have been synthesized by substitution with bromine atoms, alkyl groups, and phenyl groups, both individually and in pairs. Their fluorescence quantum yields and decay times have been measured, as well as their absorption and emission spectra and solubilities in pseudocumene. These parameters are all affected by the type, number, and position of the substituents. Quantum yields range from about 70% to less than 2% and decay times from 2.2 ns to about 100 ps. As expected, bromination reduces both quantum yield and fluorescence decay time by heavy-atom quenching. Surprisingly, asymmetrically substituted alkyl groups, which were added to increase solubility, also reduce the quantum yield and the decay time, and the effect is even larger than with bromine atoms. Symmetrical substitution with four propyl groups restored the quantum yield to approximately the value for TPB. Added phenyl groups increased the quantum yield and the decay time. In addition, aromatic solvents were found to quench the fluorescence relative to aliphatic solvents, and viscosity also plays a role. Finally, as expected, the asymmetrically substituted compounds are more soluble than the symmetrically substituted ones, and in the case of alkyl substitution, the longer the chain the greater the solubility.