Truxene, Ladder-type Indenefluorenylene Derivatives As Gain Media For Organic Lasers

The organic solid-state lasers(OSLs)have emerged as an important category of coherent sources because it can provide a new class of convenient,easily processed,and low-cost laser.However,electrical pumping is still an open challenge.Different methods have been developed to solve this problem.Developing robust organic optoelectronic materials is one of the effective solutions.Typically,conjugated small molecules/polymers have represented a class of effective organic laser materials through a long-term development.Considering the advantages of conjugated small molecules/polymers,our group has designed and developed a series of organic gain materials based on truxene and ladder-type indenefluorenylene.This paper mainly focuses on three aspects,including the systematic characterization of laser properties of truxene-cored starburst molecules,the performances comparison between the truxene-cored starburst molecules with and without the modification of diphenylamine and the efficient energy transfer in the blends of conjugated polymers.The goal is to deeply understand the optoelectronic properties and therefore broaden the application prospect in the field of OSSLs.(1)The photophysical properties of a family of materials based on truxene core with several oligofluorene arms Tr X(X=1-4)have been characterized in detail.They plays the dominant role in laser performance,such as low amplified spontaneous emission(ASE)threshold,low laser threshold,excellent light stability,thermal stability and high quantum efficiency.Compared with hybrid film that Tr X was doped Polystyrene(PS)with different doping concentrations,it was found that the optical properties of non-doped samples are superior to the doping properties,indicating that the starshaped macromolecules were endowed with its unique steric hindrance structure as an efficient,stable,low-threshold non-doped miscellaneous laser material.(2)The diphenylamine-capped materials Tr XD(X=1-3)were compared with the same series of materials Tr X.It has been found that the introduction of diphenylamine can improve the laser performance.In addition,the materials modified with diphenylamine group not only optimizes optical gain performance,but also increases the highest occupied molecular(HOMO)energy level of the materials and may greatly optimize the electrical properties of the materials.(3)The ladder-type block copolymers 2LF-BT synthesized by copolymerizing green emitting unit exhibit excellent thermal stability and good film stability.We investigated the ASE properties of a prototypical host-guest blend,namely the blue emitting poly(9,9-dioctylfluorene)(PFO)blend with ladder-type poly(indenofluorene)2LF-BT at different concentration ratio.Efficient F?rster energy transfer from the absorbing host polymer to the emitting guest polymer was observed.On one hand,the ASE threshold of the material was reduced,and the net gain was improved.On the other hand,the morphology of doped films was systematically characterized using atomic force microscopy(AFM).It was found that the morphology of the doped films was very smooth without phase separation.However,obvious phase separation was observed in the hybrid films composed of poly(9,9-dioctylfluorene-cobenzothiadiazole)(F8BT)blended with PFO.The excellent light stability and high gain characteristics demonstrated the great applicability of the ladder-type in organic laser gain medium.