Effect of linking topology on the properties of star-shaped derivatives of triazine and fluorene

Three star-shaped molecules, having 2,4,6-triphenyl-1,3,5-triazine core and fluorene side arms linked through different linkages, were designed and synthesized. The obtained compounds were characterized by UV and fluorescence spectroscopies, differential scanning calorimetry, thermogravimetric analysis, cyclic voltammetry, time-of-flight and CELIV techniques. All the three star-shaped compounds possess high thermal stability with the temperatures of the onsets of thermal degradation around 400 degrees C and glass formation ability with close glass transition temperatures (56-61 degrees C). The synthesized compounds show broadband absorption with the absorption maxima of dilute solutions in the range of 350-382 nm. Dilute solutions of the fluorenyl-substituted derivatives of 2,4,6-triphenyl-1,3,5-triazine showed monomer fluorescence with fluorescence quantum yields ranging from 0.50 to 0.70. The theoretical DFT calculations showed that the geometry, optical and electrochemical properties of the synthesized star-shaped molecules depend on their linking topologies. Thus, completely flat star-shaped molecules, in which the donor and acceptor moieties are linked through the linking bridges having double and triple bonds, are characterized by smaller optical band gap and bathochromic shift compared to the derivative with twisted skeleton in which the chromophores are linked directly via single bond. The best charge-transporting properties were shown by the compound in which 2,4,6-triphenyl-1,3,5-triazine and 2[9,9-bis(2-ethylhexyl)-9H-fluorene] moieties are linked via the linking bridges containing ethenyl linkages. Hole mobility of the amorphous layer of this compound reached 1.9 x 10(-3) cm/Vs at an electric field of 1.15 x 10(6)V/cm. (C) 2014 Elsevier B.V. All rights reserved.