Synthesis, Structures, and Photoinduced Electron Transfer Reaction in the 9,9‘-Spirobifluorene-Bridged Bipolar Systems

Exciplex-forming cohost systems with 2,7-dicyanofluorene acceptors for high efficiency red and deep-red OLEDs

Two 2,7-dicyaonfluorene-based molecules 27-DCN and 27-tDCN are utilized as acceptors (A) to combine with hexaphenylbenzene-centered donors (D) TATT and DDT-HPB for probing the exciplex formation. The photophysical characteristics reveal that the steric hindered 27-tDCN not only can increase the distance of D and A, resulting in a hypsochromic emission, but also dilute the concentration of triplet excitons to suppress non-radiative process. The 27-tDCN-based exciplex-forming blends exhibit better photoluminescence quantum yield (PLQY) as compared to those of 27-DCN-based pairs. In consequence, among these D:A blends, the device employing DDT-HPB:27-tDCN blend as the emissiom layer (EML) exhibits the best EQE of 3.0% with electroluminescence (EL) λmax of 542 nm. To further utilize the exciton electrically generated in exciplex-forming system, two D-A-D-configurated fluorescence emitter DTPNT and DTPNBT are doped into the DDT-HPB:27-tDCN blend. The nice spectral overlap ensures fast and efficient Förster energy transfer (FRET) process between the exciplex-forming host and the fluorescent quests. The red device adopting DDT-HPB:27-tDCN:10 wt% DTPNT as the EML gives EL λmax of 660 nm and maximum external quantum efficiency (EQEmax) of 5.8%, while EL λmax of 685 nm and EQE of 5.0% for the EML of DDT-HPB:27-tDCN:10 wt% DTPNBT. This work manifests a potential strategy to achieve high efficiency red and deep red OLED devices by incorporating the highly fluorescent emitters to extract the excitons generated by the exciplex-forming blend with bulky acceptor for suppressing non-radiative process.

Electron transfer across a spiro link: extreme solvatofluorochromism of a compact spiro-bridged N,N-dimethylaniline-phthalide dyad

Ultrafast intramolecular electron transfer over a spiro link leads to record-breaking solvatofluorochromism [11 600 cm⁻¹, from 357 (hexane) to 595 nm (acetonitrile)].

Design and synthesis of solution processable green fluorescent D–π–A dyads for OLED applications

Synthesized solution processable green fluorescent donor–acceptor dyads and their investigated photophysical, electrochemical, and morphological properties for OLED applications.

Synthesis of poly(spirosilabifluorene) copolymers and their improved stability in blue emitting polymer LEDs over non-spiro analogs

PHSSF-co-PDHSF exhibits blue luminescence, high quantum efficiency and thermal stability. Electroluminescence of OLEDs is more stable than non-spiro poly(silafluorene) devices.

Synthesis of dimesitylborane-substituted phenylcarbazoles as bipolar host materials and the variation of the green PHOLED performance with the substituent position of the boron atom

Two structural isomers of the bipolar host material containing the dimesitylborane moiety were synthesized and their device performance was investigated. The quantum efficiency of the devices depends on the substituent position of the dimesitylborane moiety. The maximum external quantum efficiency of the device reached as high as 23.8% with a green color coordinate of (0.30, 0.63).

Synthesis and blue phosphorescent device performances of a new bipolar host material containing pyrazino[2,3-b]indole moiety

Newly designed bipolar host material (CzPhPz) consisting of 5H-pyrazino[2,3-b]indole unit was synthesized and exhibited good electron transport properties with a high triplet energy of 2.83 eV for FIrpic-based blue PHOLEDs.

Synthesis of a highly luminescent three-dimensional pyrene dye based on the spirobifluorene skeleton

We have synthesized a highly luminescent (log e > 5.0, F > 0.9) pyrene dye based on a spirobifluorene skeleton [2,2',7,7'-tetrakis(7-tert-butyl-1-pyrenyl)-9,9'-spirobi[9H-fluorene; 4-PySBF]. The use of spirobifluorene prevents fluorescence quenching by intramolecular energy transfer and/or electron transfer among the chromophores in the excited state. The emission spectra of 4-PySBF exhibited a red shift of 20 nm in comparison to a model compound [9,9'-dioctyl-2,7-bis(7-tert-butyl-1-pyrenyl)-9H-fluorene; 2-PyF], but its UV-Vis spectrum remained unchanged.

Modulate photoinduced electron transfer efficiency of bipolar dendritic systems

Covalent linkage of dendritic carbazole-based donors and 1,3,4-oxdiazole-based acceptors renders novel bipolar dendrimers that can efficiently facilitate the photoinduced electron transfer (PET) process. Photodynamic studies indicated that the PET rate of bipolar dendrimers DA1 and DA2 can be modulated by the number of acceptors presented in the molecule.

Novel Spiro-Configured PET Chromophores Incorporating 4,5-Diazafluorene Moiety as an Electron Acceptor

[reaction: see text] We have synthesized novel spiro-bridged chromophores incorporating a 4,5-diazafluorene unit as the electron acceptor (A) and aryl amino groups as donor (D) moieties. The orthogonal D-A configuration limits ground-state D-A interactions but allows efficient PET reactions. The PET efficiency was modulated by the electronic characteristics of the donor and by the D-A distance. Preliminary studies showed that the PET process can be manipulated through metal ion complexation of the 4,5-diazafluorene moiety.

Competitive photoinduced electron transfer by the complex formation of porphyrin with cyclodextrin bearing viologen

Photoinduced electron transfer between a porphyrin and a new guest cyclodextrin bearing viologen occurs by a supramolecular formation with conformational change of a guest molecule.