Deep‐blue light‐emitting polyfluorenes with asymmetrical naphthylthio‐fluorene as Chromophores

Abstract

A novel blue polycyclic aromatic compound 2,8‐dibromo‐14,14‐dioctyl‐14H‐benzo[b]benzo [5,6] fluoreno[1,2‐d]thiophene 9,9‐dioxide (Br2NFSO) is designed and synthesized through multistep synthesis, and its structure is confirmed by nuclear magnetic resonance. Based on synthesized polycyclic aromatic compound Br2NFSO, a series of twisted blue light‐emitting polyfluorenes derivatives (PNFSOs) are prepared by one‐pot Suzuki polycondensation. Based on the twisted polymer molecular structure resulted from the asymmetric links of 14,14‐dioctyl‐14H‐benzo[b]benzo[5,6]fluoreno[1,2‐d]thiophene 9,9‐dioxide (NFSO) unit in copolymers and better electron transport ability of NFSO than those of the electron‐deficient dibenzothiophene‐S,S‐dioxide counterpart, the resulting polymers exhibit excellent electroluminescent spectra stability in the current densities from 100 to 800 mA cm−2, and show blue‐shifted and narrowed electroluminescent spectra with the Commission Internationale de L′Eclairage (CIE) of (0.16, 0.07) for PNFSO5, compared to poly(9,9‐dioctylfluorene) (PFO) with the CIE of (0.18, 0.18). Moreover, the superior device performance is achieved based on PNFSO5 with the maximum luminous efficiency (LEmax) of 1.96 cd A−1, compared with the LEmax of 0.49 cd A−1 for PFO. The results indicate that the twisted polycyclic aromatic structure design strategy has a great potential to tuning blue emission spectrum and improving EL efficiency of blue light‐emitting polyfluorenes. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 171–182

Diarylfluorene Flexible Pendant Functionalization of Polystyrene for Efficient and Stable Deep-Blue Polymer Light-Emitting Diodes

“…As we expected, the external quantum efficiencies (EQE) of the PS-MC8TPA-based device also improved from 0.72 to 1.15%, enhanced about 60% after thermal annealing, but decreased from 2.72 to 0.14% for MC8TPA pristine and annealed ones. In this regard, our PLED presents comparable performance to the many previous deep-blue PLEDs. − A diphenylvinyl-bearing copolymer PLED exhibited a peak luminous efficiency of 2.21 cd/A, and the device based on 1,4-polynaphthalene copolymers presented a similar performance with a CE and EQE of 5.76 cd/A and 1.18%, respectively. In fact, Monkman et al also obtained a series of fluorene-based deep-blue polymers whose corresponding PLEDs also have an EQE of 1.4 and 3.2% and a CE of 0.65 and 4.4 cd/A for the para-conjugated and F-S copolymers. ,, In addition, the ultrahigh-performance deep-blue PLEDs are also reported in previous studies (∼7.3 cd/A, >5%). − As we know, solution-processed deep-blue PLED device performances are determined by many factors, such as the film morphology, energy level, PLQY, and device fabrication technique.…”

Influence of Regioregularity on the Optoelectronic Properties of Conjugated Diketopyrrolopyrrole Polymers Comprising Asymmetric Monomers

“…Advancements in the design and synthesis of semiconducting conjugated polymers are the main contributor to the excellent performance of modern organic electronic devices. − A major breakthrough in the design of conjugated polymers was achieved by the D–A approach, in which electron donating (D) and electron accepting (A) units are alternating along the conjugated polymer backbone to tune the optoelectronic properties such as orbital energy levels and optical bandgap. , …”

Efficient deep‐blue light‐emitting polyfluorenes based on 9,9‐dimethyl‐9H‐thioxanthene 10,10‐dioxide isomers

“…To enable access to deep‐blue PLEDs and improve the comprehensive performance of PFs, electron‐withdrawing units (e.g., 1,3,4‐oxadiazole, 1,2,4‐triazole, 2,4,6‐triphenyl pyridine, dibenzothiophene‐ S , S ‐dioxide (SO)) have been introduced into polymer backbones or side chains to enhance electron injection and balance charge transport 15–19 . Weak conjugate‐structured 20–21 or twisted polymer backbones 22–24 have also been designed to interrupt the conjugation of the polymer backbone and thereby achieve deep‐blue emission. However, incorporation of electron‐withdrawing groups into the polymer backbone leads to charge‐transfer (CT) from electron‐rich units to electron‐withdrawing groups, which results in bathochromic spectra and influences the color purity of blue emission 25,26 .…”