Green‐Light‐Emitting Poly(Spirobifluorene)s with an Electron‐Rich Unit in the Side Chain and an Electron‐Deficient Unit in the Main Chain

Abstract

Poly(spirobifluorene)s and their derivatives with three primary colors are promising for application in efficient and stable polymer light‐emitting diodes (PLEDs). Here, a novel approach is reported to tune the emission colors of blue‐light‐emitting poly(spirobifluorene)s through a charge‐transfer mechanism from the side chain to the main chain. By using the electron‐rich 2,3,6,7‐tetra‐octyloxyfluorene unit as the side chain and incorporating the electron‐deficient dibenzothiophene‐S,S‐dioxide (SO) unit into the main chain, a series of polyspirobifluorene derivatives are successfully developed. They all display efficient green photoluminescence and electroluminescence. The observed green emission can be ascribed to both intramolecular and intermolecular charge transfer from the pendant 2,3,6,7‐tetra‐octyloxyfluorene unit to the SO unit in the main chain. Single‐layer PLEDs of these polymers reveal a maximum luminance efficiency of 1.99 cd A−1 and a maximum power efficiency of 1.30 lm W−1 with Commission Internationale de L'Eclairage coordinates of (0.37, 0.54).

Tunable charge transfer effect in poly(spirobifluorene)s with different electron-rich side chains

“…For example, when the electron-deficient dibenzothiophene-S, S-dioxide (DBTSO) unit is incorporated into the main chain of 4RO-PSF, a strong CT from the pendant 2,3,6,7-tetraoctyloxyfluorene to the main chain is found to be responsible for the green emission. 10 Furthermore, when DBTSO is replaced by its nonconjugated analogue, diphenylsulfone (DPSO), the CT strength is then inhibited due to the lower electron affinity of DPSO relative to DBTSO. Hence, blue-emitting PSFs is successfully achieved with a promising luminous efficiency of 2.90 cd A −1 as well as Commission Internationale de L'Eclairage (CIE) coordinates of (0.17, 0.18).…”

Deep‐blue light‐emitting polyfluorenes containing spiro[fluorene‐9,9′‐thioxanthene‐S,S‐dioxide] isomers

“…It suggests that there is a stronger ICT effect, which can be attributed to the direct links between sulfonyl and fluorene conjugated backbone. It is impressive that the bathochromic shift of PPF‐SOFs is much weaker than other polymers containing sulfonyl moiety . The suppressed ICT interaction is owing to the existence of sp 3 hybridized carbon in SOF which breaks the conjugation of polymers …”

Backbone‐Acceptor/Pendant‐Donor Strategy for Efficient Thermally Activated Delayed Fluorescence Conjugated Polymers with External Quantum Efficiency Close to 25% and Emission Peak at 608 nm

“…The S moiety with two sulfone groups is a classical acceptor, which can raise the T 1 energy level through interrupting the conjugation of the polymer backbone besides improving the polymer solubility. [30][31][32] Based on these considerations, the monomer 2Br-AQF (M 1 ) was synthesized according to the literature procedures (Scheme S1, Supporting Information) with 1,2-difluorobenzene as the starting material. [33,34] To manage the molar content of the TADF unit, 3,7-substituted S borate (M 3 ) was smoothly prepared from the monomer 2Br-S (M 2 ) and bis(pinacolato)diboron via Pd-catalyzed exchange reaction.…”