Boosting the Stimulated Emission Properties of Host:Guest Polymer Blends by Inserting Chain Twists in the Host Polymer. (7th September 2022)

• Record Type: Journal Article
• Authors: Sun, Chen; Bai, Lubing; Roldao, Juan Carlos; Burgos‐Caminal, Andrés; Borrell‐Grueiro, Olivia; Lin, Jinyi; Huang, Wei; Gierschner, Johannes; Gawelda, Wojciech; Bañares, Luis; Cabanillas‐González, Juan
• Is Part Of: Advanced functional materials. Volume 32:Number 48(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-09-07
• Subjects: amplified spontaneous emissions -- dihedral angles -- excited‐state dynamics -- optical gain -- polymer chains -- pump‐probes; Materials -- Periodicals; Chemical vapor deposition -- Periodicals; 620.11
• DOI: 10.1002/adfm.202206723
• Languages: English
• ISSNs: 1616-301X

Abstract

Abstract: Conjugated polymer blends coupled by Förster resonance energy transfer (FRET) have been widely exploited to achieve optically pumped lasers operating at very low pumping thresholds. Among the plaid of conjugated polymers and molecules exploited for optical gain, fluorene‐based polymers are considered front‐runners, based on their high photoluminescence quantum yields, large optical gain coefficients, and their processability assets in films of high optical quality. Two archetypes of polymers with these properties are poly(9, 9‐dioctyl‐fluorene) and its green‐emitting relative poly(9, 9‐dioctylfluorene‐alt‐benzothiadiazole) that work as excellent FRET‐coupled blends but unexpectedly do not exhibit stimulated emission. In this study, light is shed upon the optical gain limiting factors of these blends. Upon investigating a series of poly(diarylfluorene‐co‐N‐phenyl) polymers bearing a different number of phenyl units inserted between the fluorenes (NPhs, N = 1, 2, 3), important improvements are revealed in the photoluminescence quantum yields and stimulated emission properties, as well as harnessing of exciton‐exciton annihilation. These effects are ascribed to disruption of exciton transport in NPhs motivated by changes in chain conformation and molecular packing upon phenyl‐insertion. Abstract : Singlet‐singlet annihilation and polaron absorption jeopardize optical gain in fluorene‐based blends coupled by Förster resonance energy transfer. Upon the systematic insertion of twisting units in the backbone, singlet‐singlet annihilation is mitigated and polaron by‐products are neutralized, releasing guest stimulated emission from detrimental polaron absorption.