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Authors :
Han Y., Sun C., Bai L., Zuo Z., Xu M., Yu M., An X., Wei C., Lin J., Wang N., Ou C., Xie L., Ding X., Cabanillas-Gonzalez J., Huang W.; Yamin Han Chen Sun Lubing Bai Zongyan Zuo Man Xu Mengna Yu Xiang An Chuanxin Wei Jinyi Lin Wang Changjin Ou Linghai Xie Xuehua Ding Juan Cabanillas-Gonzalez Huang Laboratory of Flexible Electronics (KLOFE) & Institute of Advanced Materials (IAM) & School of Physical and Mathematical Sciences Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM) Nanjing Tech University (NanjingTech) 30 South Puzhu Road Nanjing 211816 China Centre for Molecular Systems and Organic Devices (CMSOD) Key Laboratory for Organic Electronics and Information Displays & Institute of Advanced Materials (IAM) Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM) Nanjing University of Posts & Telecommunications 9 Wenyuan Road Nanjing 210023 China Madrid Institute for Advanced Studies (IMDEA Nanociencia) Ciudad Universitaria de Cantoblanco Calle Faraday 9 Madrid 28049 Spain Shaanxi Institute of Flexible Electronics (SIFE) Northwestern Polytechnical University (NPU) 127 West Youyi Road Xi'an Shaanxi 710072 China amplified spontaneous emissions ultrafast transient absorption spectroscopy intramolecular excited states matrix encapsulation thiophene-based fluorophores National Natural Science Foundation of China 61874053 61805117 21502091 21502092 21774061 National Key Basic Research Program of China (973) 2015CB932200 Natural Science Funds of the Education Committee of Jiangsu Province 18KJA430009 Natural Science Foundation of Jiangsu Province BK20171470 'High-Level Talents in Six Industries' of Jiangsu Province XYDXX-019 Key Laboratory for Organic Electronics State Key Laboratory of Supramolecular Structure and Materials sklssm2019017 Program for Postgraduates Research Innovation in University of Jiangsu Province KYCX17-0752 KYCX18-1121 Spanish Ministry of Economy and Competitiveness MAT2014-57652-C2-1 2-R (LAPSEN) PCIN-2015-169-C02-01/02 (MOFSENS) Severo Ochoa Programme for Centers of Excellence SEV-2016-0686 Campus of International Excellence (CEI) UAM+CSIC. J. C-G. China Scholarship Council 201608390023 Supplementary Precise control of exciton behavior is key in constructing high?performance material systems for optoelectronic applications. Intrinsic sulfur in building aromatic units always results in strong aggregation, which causes exciton quenching, polaron formation, and enhanced nonradiative components. Herein, a series of solution?processed thiophene?based diarylfluorene derivatives is demonstrated and these fluorophores are encapsulated in the matrix system to suppress polaron formation for efficient green and red amplified spontaneous emission (ASE). A systematic photophysical study in solution, neat films, and polystyrene (PS)?based encapsulated systems reveals that their emission behaviors are substantially promoted in PS encapsulated matrix due to the suppressed intermolecular aggregation. Furthermore, fs?transient absorption (TA) measurements confirm that the encapsulated systems present stimulated emission (SE) and obtain the same intramolecular excited?state character to those in solution, associated with the effective suppression of polaron formation and exciton quenched, in opposition to neat films with broad photoinduced absorption (PA) bands. Therefore, in contrast to the neat spin?coated film without gain processing, these encapsulated systems give rise to notable optical gain properties with threshold values for green and red ASE as low as 70??J?cm ?2 . Molecular encapsulation is an effective strategy to precisely enhance exciton behavior and emission efficiency for optoelectronic applications. Amplified spontaneous emission (ASE) properties of four sulfur?containing diarylfluorene derivatives (i.e., MC8?BT, MC8?TBT, MC6Cz?BT, and MC6Cz?TBT) are investigated. High?quality spin?coated films with promoted photoluminescence quantum efficiency values are obtained as a result of intramolecular emission confined in the polystyrene (PS) matrix. Furthermore, PS?doped films exhibit a rather low ASE threshold. In light?emitting devices, intermolecular interactions often result in color impurity, spectral instability, and lower luminescence efficiency, which are undesirable for organic lasers and organic light?emitting diodes (OLEDs). In particular, a major challenge for solution?processed thiophene (Th)?based donor–acceptor emitters is their low photoluminescence quantum efficiency (PLQE) in the solid state, which drops to less than ?4% from ?40% typically observed in solution. Beyond the nonradiative decay paths at the single molecule level, new PLQE loss mechanisms appear in the condensed state, such as the formation of weakly emissive intermolecular states or diffusion?assisted quenching processes involving exciton trapping and dissociation, singlet–singlet, and singlet–triplet annihilation. Blocking exciton diffusion by inducing spatial exciton confinement has shown to be effective in promoting the photoluminescence and optical gain properties of conjugated polymers. Luminescence quenching caused by the intermolecular coupling of excited states can be efficiently suppressed by spatially confining the fluorophores into host matrices. Matrix dispersion of conjugated molecules can, in addition, endow the blend with excellent processability, mechanical, and environmental stability properties of interest for optoelectronic devices. The performance of organic optoelectronic devices depends significantly on the film nanostructure. a. The asymmetric substitutions on either side of the fluorene not only merely introduce large steric hindrance (9?position) but also enhance the solution processability (4?position). With the aim to enhance the light?emitting properties of the compounds, we encapsulated the luminescent molecules in polystyrene (PS) (Scheme b), observing amplified spontaneous emission (ASE) with remarkably low thresholds, in contrast with ASE absence in neat films. Ultrafast transient absorption (TA) spectroscopy was deployed in combination with ASE measurements on the solution, neat films, and matrix system to elucidate the molecular encapsulation and confinement effect on the photophysics and optical gain properties of the novel compounds. In neat films, the absence of stimulated emission (SE) is concomitant with a new photoinduced absorption (PA) band which confirms the interplay of absorbing intermolecular excited states. The encapsulation of Th?based molecules in PS restores the SE band primarily observed in solution and confirms that intermolecular excited states play no significant role in blends. In this work, we synthesized two series of novel green and red fluorescent molecules via the Suzuki reaction based on the platform of diarylfluorene, MC8?BT, MC8?TBT, MC6Cz?BT, and MC6Cz?TBT, as shown in Scheme a) Chemical structures of novel Th?based diarylfluorene compounds. b) Schematic illustration of the matrix encapsulation in PS and the characterization of the ASE properties of blends.
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Source:
Repositorio Institucional del Instituto Madrileño de Estudios Avanzados en NanocienciaInstituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA Nanociencia)
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