Abstract
Four D-π-A conjugated polymers, namely P1–P4, which contain benzotriazole building blocks in their backbone as acceptor, are synthesized via palladium-catalyzed direct C-H cross-coupling polycondensation of 5,6-difluorobenzotriazole with different thiophene derivatives, including 3-octylthiophene, 2,2’-bithiophene, thieno[3,4-b][1,4]dioxine, and 4,4-dioctyl-4H-silolo-[3,2-b:4,5-b’]dithiophene as donor units, respectively. Taking the polymer P1 as an example, the chemical structure of the polymer is demonstrated by 1H and 19F NMR spectra. The optical, electrochemical, and thermal properties of these polymers are assessed by UV–vis absorption and fluorescence spectroscopy, cyclic voltammetry (CV), and thermal gravimetric analysis (TGA), respectively. DFT simulations of all polymers are also performed to understand their physicochemical properties. Furthermore, P1 and P2, which have relatively higher molecular weights and better fluorescent quantum efficiency than those of P3 and P4, are utilized as lighting emitters for organic light-emitting diodes (OLEDs), affording promising green and red luminescence with 0.07% and 0.14% of maximum external quantum efficiency, respectively, based on a device with an architecture of ITO/PEDOT:PSS/PTAA/the polymer emitting layer/TPBi/LiF/Al.
Highlights
Organic light-emitting diodes (OLEDs) have received much attention both in academia and industry owing to their wide applications in fullcolor displays and solid-state lighting. π-Conjugated polymers have many unique photophysical properties that are inherited from the delocalized electronic structures of their backbones and, they exhibit promising advantages, such as solution-processing, light-weight, low-cost, and facile preparation of flexible devices in various functional applications, such as OLEDs, solar cells, field-effect transistors (FETs), photodetectors, etc. [1,2,3,4,5,6]
As depicted in Scheme 1, P1–P4 were prepared by Pd-catalyzed direct C-H crosscoupling reaction of 5,6-difluoro-2-(2-hexyldecyl)-2H-benzotriazole (1) with four different thiophene derivatives, including 3-octylthiophene, 2,2’-bithiophene, thieno[3,4-b][1,4] dioxine, and 4,4-dioctyl-4H-silolo-[3,2-b:4,5-b’]dithiophene under the optimized conditions as reported in our recent work [29], namely, Pd(OAc)2 (10 mol%) as catalyst, Ag2CO3 (3.0 equiv) as oxidant, K2CO3 (3.0 equiv) as base, PivOH (2.0 equiv) as additive, and DMAc/xylene (v/v, 10/1) as solvents at 110 ◦C for 48 h
As depicted in Scheme 1, P1–P4 were prepared by Pd-catalyzed direct C-H crosscoupling reaction of 5,6-difluoro-2-(2-hexyldecyl)-2H-benzotriazole (1) with four different thiophene derivatives, including 3-octylthiophene, 2,2’-bithiophene, thieno[3,4-b][1,4]dioxine, and 4,4-dioctyl-4H-silolo-[3,2-b:4,5-b’]dithiophene under the optimized conditions as reported in our recent work [29], namely, Pd(OAc)2 (10 mol%) as catalyst, Ag2CO43o(f31.20 equiv) as oxidant, K2CO3 (3.0 equiv) as base, PivOH (2.0 equiv) as additive, and DMAc/xylene (v/v, 10/1) as solvents at 110 °C for 48 h
Summary
Organic light-emitting diodes (OLEDs) have received much attention both in academia and industry owing to their wide applications in fullcolor displays and solid-state lighting. π-Conjugated polymers have many unique photophysical properties that are inherited from the delocalized electronic structures of their backbones and, they exhibit promising advantages, such as solution-processing, light-weight, low-cost, and facile preparation of flexible devices in various functional applications, such as OLEDs, solar cells, field-effect transistors (FETs), photodetectors, etc. [1,2,3,4,5,6]. In 2014, several benzotriazole-containing π-conjugated polymers were achieved through Stille coupling reaction of 4,7-dibromo-5,6difluorobenzotriazole with 2,5-bis(trimethylstannyl)thiophene derivatives for polymer fieldeffect transistors (FETs) applications [11] These synthetic methods above for benzotriazolebased π-conjugated polymers generally require halogenations and/or organometallic prefunctionalization steps of the corresponding monomers prior to polymerization. Transition-metal catalyzed direct C-H coupling strategy was proposed and has been applied for preparing various π-conjugated polymers, including our work [13,14,15,16,17] This synthetic protocol fully avoids the steps of pre-functionalized starting monomers, and allows straightforward access to πconjugated polymers [13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28]. Tetrabutylammonium phosphorus hexafluoride (Bu4NPF6) with a concentration of 0.1 M in CH3CN was applied as the support electrolyte
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