Juae Kim

2,2-dimethyl-2H-benzimidazole based small molecules for organic solar cells

We report the small molecules utilizing new electron-deficient unit, 2,2-dimethyl-2H-benzimidazole (MBI) and phenanthro[9,10-c][1,2,5]thiadiazole (PT), for the photovoltaic application. Donor-acceptor-donor (D-A-D) types of conjugated small molecules containing benzo[1,2-b;3,4-b′]dithiophene (BDT) as electron rich unit and MBI and PT as electron deficient units (SM1 and SM2) were synthesized. D-A-D type of small molecules has the abilities of increasing intramolecular charge transfer (ICT) inducing long wavelength absorption and lowering the HOMO level for the improvement of open-circuit voltage (VOC). SM1 was synthesized by coupling BDT and PT units by Stille coupling reaction with Pd(0)-catalyst. By using same type of Pd(0)-catalized reaction, BDT unit and MBI unit linked with two thiophenes were coupled to provide SM2. The spectrum of SM2 in the solid thin film shows absorption band with maximum peak at 601 nm and the absorption onset at 756 nm, corresponding to band gap of 1.64 eV. The device comprising SM2 with PCBM (3:7) showed a VOC of 0.62 V, a JSC of 1.69 mA/cm2, and a fill factor (FF) of 0.27, giving a power conversion efficiency of 0.28%.

Synthesis and properties of low band gap polymers based on thienyl thienoindole as a new electron-rich unit for organic photovoltaics

A series of polymers based on 6-(2-thienyl)-4H-thieno[3,2-b]indole (TTI), a new electron-rich unit for organic photovoltaics, was synthesized. By replacing the six-membered benzene ring of the carbazole with an electron-rich five-membered thiophene ring, an enhanced ICT effect between the electron-rich group and the electron-deficient group is expected to result in improved π-electron delocalization, low band gap and increased light-harvesting ability of the OPVs. The TTI unit, with a fused rigid backbone, has an efficient structure for the ICT effect and for tuning of the HOMO and LUMO energy levels to generate a low band gap. As electron-deficient units, 4,7-bis(4-hexylthiophen-2-yl)-2,1,3-benzothiadiazole (DTBT-h), 2-dimethyl-4,7-di(2-thienyl)-2H-benzimidazole (DTMBI) and 3,6-di(2-thienyl)-2,5 dihydropyrrolo[3,4-c]pyrrole-1,4-dione (DPP) were introduced by using Stille polymerization. PTTIDTMBI and PTTIDPP have low band gaps and show absorption up to 849 and 948 nm, respectively. The highest PCE was achieved with the device fabricated from a PTTIDTBT-h : PC71BM (1 : 3 w/w) blend with 1,8-octanedithiol (ODT) as an additive. The device demonstrated a Voc value of 0.81 V, a Jsc value of 8.19 mA cm−2, and an FF of 0.51, giving a highest power conversion efficiency of 3.35%.

Tumor necrosis factor-α and interleukin-1β expression pathway induced by Streptococcus mutans in macrophage cell line RAW 264.7

Streptococcus mutans, a major etiological agent of dental caries, frequently causes systemic disease, such as subacute bacterial endocarditis, if it enters the bloodstream. In this study, the production pathways of the proinflammatory cytokines, tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β), induced by S. mutans in mouse macrophage were examined using a quantitative real-time polymerase chain reaction and an enzyme-linked immunosorbent assay. The S. mutans stimulated the expression of TNF-α and IL-1β mRNA at a multiplicity of infection of 1 : 100, which increased at 2 and 4 h, respectively, to 24 h. It also induced the production of high levels of the TNF-α and IL-1β proteins, which increased at 2 h and reached a peak at 4 and 24 h, respectively. Nuclear factor-κB (NF-κB) was activated and reached a maximum level 30 min after the S. mutans treatment. The expression of TNF-α and IL-1β mRNA and protein was suppressed by the treatment with pyrrolidine dithiocarbamate, an NF-κB inhibitor. The S. mutans-induced TNF-α expression was suppressed by the presence of SB203580, a p38 mitogen-activated protein (MAP) kinase inhibitor, or SP600125, a Jun N-terminal kinase (JNK) MAP kinase inhibitor. On the other hand, IL-1β expression was inhibited by extracellular signal-regulated kinase (ERK)/p38/JNK MAP kinase inhibitor pretreatment. In addition, TNF-α production was suppressed more in the Toll-like receptor 2(-/-) (TLR2(-/-)) macrophages than in the TLR4(-/-) macrophages, whereas IL-1β production was suppressed more in the TLR4(-/-) macrophages than in the TLR2(-/-) macrophages. These results show that S. mutans stimulates the production of TNF-α and IL-1β in the mouse macrophage cell line, RAW 264.7, by activating ERK/p38/JNK, and NF-κB through TLR2 and TLR4, respectively.

Syntheses and Properties of Semiconducting Polymers Based on Pyrimidine Series Substituted with Thiazolo-Pyridine

For the utilization in the polymer solar cells, conjugated polymers were synthesized using electron-deficient units, 2-{3-[4,6-bis-(4-hexyl-thiophen-2-yl)-pyrimidin-2-yl]-phenyl}-thiazolo[5,4-b]pyridine (mTP) or 2-{4-[4,6-bis-(4-hexylthiophen-2-yl)-pyrimidin-2-yl]-phenyl}-thiazolo[5,4-b]pyridine (pTP). To increase the electron-deficiency of the pyrimidine unit, thiazolopyridine (TP), strong electron-withdrawing group, was incorporated at the meta-/para-position of the phenylene connector which is attached to the pyrimidine. It was confirmed that the TP unit at para-position has stronger intramolecular charge transfer (ICT) effect to shift the absorption to the longer wavelength region and deepens the highest occupied molecular orbital (HOMO) energy level. The polymers with 4-(1-octylnonyl)-6-(2-thienyl)-4H-thieno[3,2,-b]indole (TTI) having the decent solubility for the morphology show the superior open-circuit voltage (VOC) value of the mTTI/pTTI devices compared to the others. Also, the polymers with TTI show increased short-circuit current (JSC), fill factor (FF), and power conversion efficiency (PCE) due to high face-on populations.