A New Class of Solution Processable Pyrazino[2,3‐g]quinoxaline Carbazole Derivative Based on D–A–D Architecture for Achieving High EQE in Yellow and White OLEDs

Abstract

level. Carbazole-containing polymers were used as organic light-emitting diodes, [1][2][3] photovoltaic cells, [4,5] and thin-film transistors. [6,7] They have also found application in electrochromic devices as they can form relatively stable cations on the application of voltage. [8,9] Carbazole-based compounds also found application in the synthesis of several thermally activated delayed fluorescence (TADF) materials, which are capable of enhancing the emission efficiency of present-day organic light-emitting diodes (OLEDs) by harvesting the excitons in a triplet state. [10,11] However, the realization of such beneficial materials requires the proper combination of carbazoles with suitable acceptor units with a twisted structure with a reduced energy gap between the singlet and triplet states. Carbazoles are also utilized as donor units in donor-acceptor (D-A) compounds with a high potential for synthetic tunability, ambipolar charge transport, and light-emitting materials with high emission efficiency. [12][13][14][15] A wide variety of carbazole derivatives are used in fluorescent and phosphorescent OLEDs due to their suitable energy levels, good charge transport behavior, and high triplet energies as host materials. [16][17][18][19][20][21] Being an inexpensive, stable starting material with the ease of functionalization by N-alkylation and core modification, carbazole provides enormous opportunities for structural modifications to realize functional materials. [22] Quinoxaline derivatives also have been used in organic electronic devices like organic solar cells, [23,24] OLEDs, [25] and organic field effect transistors (OFETs). [26] They have also found application in the construction of supramolecular self-assembling materials, [27] sensors, [28] and also as acceptor units in the building of D-A systems with low energy gaps. [29] Pei and co-workers developed tetrasubstituted pyrazino[2,3g]quinoxaline derivatives with thiophene and phenyl rings, which leads to varying extent of conjugation to achieve highefficiency active waveguide fibers. [30] Grimsdale and co-workers further extended the conjugation and introduced substituents at the quinoidal positions to study the electronic properties of the pyrazino[2,3-g]quinoxaline derivatives. [31] A water-soluble pyrazino [2,3-g]quinoxaline based photosensitizer reported by A new pyrazino[2,3-g]quinoxaline carbazole derivative with branched alkyl peripheral chains PQC-12b with a donor-acceptor-donor nonplanar architecture is reported. PQC-12b exhibits high molar extinction coefficients, low bandgap, bright emission behavior in solution and solid-state, along with positive solvatochromism. PQC-12b is used in organic light-emitting diodes (OLEDs) either as sole emissive material or as a guest in different host materials. Amongst these different host-guest OLEDs, CBP-based device with the optimized concentration of PQC-12b shows maximum values for power efficacy (PE max ) of 14.1 lm W −1 , current efficacy of 26.8 cd A −1 , external quantum efficiency (EQE max ) of ...

Benzoxazole-Based Hybridized Local and Charge-Transfer Deep-Blue Emitters for Solution-Processable Organic Light-Emitting Diodes and the In fluences of Hexahydrophthalimido

“…The maximum EQE of BPCPCHY was 3.39%, which was nearly 2.5 times higher than that of BPCP (1.38%) (Figure S19c). This unsatisfactory performance of doped OLEDs (EQE max < 5%) may be due to leakage of charge carriers and hole and electron injection mismatches, allowing carriers to enter the emission layer unevenly. , …”

“…This unsatisfactory performance of doped OLEDs (EQE max < 5%) may be due to leakage of charge carriers and hole and electron injection mismatches, allowing carriers to enter the emission layer unevenly. 57,58 To improve the electroluminescence performance of OLEDs, we further investigated the effect of the doped host materials and concentration. Thus, the benzoxazole-based doped OLEDs were improved through optimization of BPCP and BPCPCHY concentrations doped into mCP host materials.…”

Progresses and Perspectives of Near-Infrared Emission Materials with “Heavy Metal-Free” Organic Compounds for Electroluminescence

“…In 2012, Wang et al [ 43 ] obtained a family of D-A-D type NIR fluorophores (4,9-Bis[4-(1,2,2-triphenylvinyl)phenyl][1,2,5]thiadiazolo-[3,4-g]-quinoxaline ( M19 ), 4,9-Bis{4-[2,2-bis(4-methoxyphenyl)-1-phenylvinyl]phenyl}[1,2,5]thiadiazolo-[3,4-g]quinoxaline ( M20 ), 4,8-Bis[4-(1,2,2-triphenylvinyl)phenyl]benzo[1,2-c:4,5-c′]bis-[1,2,5]thiadiazole ( M21 ) and 4,8-Bis{4-[2,2-bis(4-methoxyphenyl)-1-phenylvinyl]phenyl}benzo-[1,2-c:4,5-c′]bis[1,2,5]thiadiazole ( M22 )) containing rigid nonplanar conjugated tetraphenylethene (TPE) moieties with electron-deficient [1,2,5]thiadiazolo[3,4-g]quinoxaline (QTD) or BBTD as acceptors ( Figure 10 ). A twisted TPE had the excellent aggregation-induced emission enhancement (AIEE) and showed a higher fluorescence efficiency in the solid state than in solution [ 111 , 112 , 113 ]. So incorporation of TPE units into the chemical structures of poor fluorophores could improve their fluorescence efficiency in the solid state significantly.…”

White light emission generated by two stacking patterns of a single organic molecular crystal

“…Most examples reported so far have relied on combinations of multiple components with emission colours that cover the entire visible range. [11][12][13] Compared to these mixed dyes, single-molecule white light emitters (SMWLEs) are expected to exhibit superior performance without segregation or colour degradation as well as improved reproducibility. [14][15][16][17] White light emission by a single molecule requires simultaneous dual or ternary emission.…”