The Design And Synthesis Of Organic Gain Media And The Study Of Their Stimulated Emission

Organic gain media play an important role in the development of organic semiconductor lasers,especially for the realization of electrically pumped organic laser.In this thesis,we introduced some methods,such as chemical group with high photoluminescence efficiency,large plane?-conjugated structure,and building energy transfer system,to design and synthesize novel organic gain media combining with the advantages of low ASE/laser threshold,high thermal/optical stability,high gain value,high PLQY,high charge carrier mobility,and so on.By fabricating organic light-emitting diodes and laser device integration,we studied the electroluminescence properties,stimulated emission behaviors,laser performances,and the relationships between chemical structures and optical properties in the organic gain media.Specfically,the doctoral dissertation was divided into seven chapters.In Chapter 1,we introduced the development of organic solid-state lasers,the building block of lasers,and the mechanisms of stimulated emission.The optical feedback structures were also introduced.Then,a comprehensive overview of organic gain media was presented.We highlighted the efforts and strategies to overcome problems associated with electrical pumping of organic lasers.At last,the research motivations and main studies of this dissertation were put forward thereupon.In Chapter 2,a new series of pyrenyl-capped benzofiurene derivatives?PFP-X,X=1-3?were designed,synthesized and investigated as model compounds for understanding the effects of flexible side chains on modulating the functional properties of organic semiconductors for optoelectronics.The results emphasized that the increase of flexible chain lengths effectively decreased intermolecular interactions and depressed the crystalline nature,which could endow the corresponding materials with improved morphology properties,and optical physical characterstics.Also,the pyrenyl-capped benzofiurene derivatives exhibited excellent electroluminescence proformance and stimulated emission behaviors.The very low laser thresholds were achieved.In Chapter 3,we presented a design strategy to explore a novel series of monodisperse star-shaped ladder-type macromolecules,named as TrL-n?n=1-3?.The novel star-shaped systems were composed of truxene as the central core,three fused ladder-type oligo?p-phenylene?arms with varying?-conjugated length and diphenylamine units as functional end-cappers with the aim to achieve excellent structural perfection free of chemical defects.The star-shaped ladder-type compounds exhibited enhanced optical stability and suppressed low-energy emission.Superior low ASE thresholds were recorded for TrL-n,demonstrating their promising potential as excellent gain media.In Chapter 4,we proposed a novel molecular design strategy with the aim to explore robust organic gain media for organic lasers.A novel series of spiro-fused star-shaped ladder-type macromolecules?named as SpL-n,n=1-3?were thus designed,synthesized and investigated.By taking the synergetic effects of the key building blocks in the spiro-fused ladder-type structure,the resulting materials exhibited excellent structure perfection,good stability and prominent ASE/laser performance.More significantly,very high gain coefficient values(>170 cm^-1)were determined,which were the highest ever reported based on the?-conjugated material systems.The study showed that,this ingenious molecular architecture with excellent stability,high gain and attractive lasing behavior would undoubtedly shed light on exploring robust organic gain media towards organic electrically-pumped lasers.In Chapter 5,we selected spiro-fused ladder-type molecules?SpL?1?-x,SpL?2?-y,SpL-z,x,y,z=1-3?as working platform to understand the molecular configuration effects in optical properties,especially in the performance of stimulated emissions.Compared with linear spiro-fused ladder-type molecules,star-shaped ladder-type macromolecules?SpL-n?exhibited lower ASE thresholds,superior better ASE optical/thermal stabilities,and gain properties.In Chapter 6,we presented a novel concept to construct triplet-singlet guest-host systems with incorporating iridium complexes as the triplet harvesters and a fluorescent conjugated polymer?F8BT?as the gain media to achieve light amplification.Successful light amplification with three-fold lower ASE threshold and much better lasing performance were demonstrated for the resulting triplet-singlet guest-host system as compared with the corresponding gain system without triplet harvester.The work suggested an effective general methodology to utilize the triplet excitons to contribute to the light amplification with excellent electrical performance in organic light-emitting diodes,opening the prospects towards attempting organic semiconductor laser diodes.In Chapter 7,the conclusion and prospect have been summarized.