Efficient amplified spontaneous emission based on π-conjugated fluorophore-cored molecules studied by density functional theory

The π-conjugated molecules, anthracene, pyrene and perylene with stepwise enhanced conjugation, have become a key ingredient in the design of new organic semiconductors for light emission and energy harvesting applications. Here, new biphenyl dissubstituted anthracene, pyrene and perylene derivatives are synthesized and investigated as blue-emitting materials. The designed molecules exhibited typical amplified spontaneous emission (ASE) behavior in solid thin films for the compounds dispersed in the inert polystyrene host at a rather large (5 wt%) chromophore concentration. Theoretical analysis assists in understanding the emission properties and optical gain performance. The calculations reveal enhanced transition density and increased transition dipole moment accompanying by stepwise enhanced molecular conjugation of fluorophore-cores. In addition, enhanced fluorescence quantum yield, significant shortened fluorescence lifetimes and increased radiative decay rate for designed compounds promote the occurrence of ASE behavior compared with anthracene, pyrene and perylene. As well, the vibration analysis show that the intramolecular vibrational modes of researched molecules possessed small Huang-Rhys factors, which thus bring in effective competition between radiative and non-radiative decay process in favor of optical gain. The experimental and theoretical provide evidence that the reported molecules are promising candidates for organic laser applications.