Fluorene-based conjugates with geminal donor-acceptor: synthesis, photophysical properties and theoretical studies

We report six new 2,6-disubstituted fluorene-based conjugated molecules carrying orthogonal triphenylamine and pyridine moiety as donor-acceptor units at the C-9 position. The geminal donor-acceptor is connected to the fluorene core by sigma-conjugation. Optical/solvatochromic studies, investigated by UV-VIS absorption and fluorescence spectroscopy, show blue emission with good quantum yield (40-70%) in solution and in thin film state for the synthesized compounds. In microsecond order, the derivatives give a shorter delayed lifetime (both in solution and thin films), facilitating reverse intersystem crossing (RISC). TD-DFT studies for all the derivatives show minimal singlet-triplet splitting in the gas phase (close to 0.2 eV), and the high thermal stability confirmed by the compound's TGA method (320-398 degrees C) makes them very useful in the optoelectronic market.