A novel light-emitting hydrogen-bonded (H-) acceptor PBB (M1) containing three conjugated aromatic rings, including one pyridyl terminus and two lateral methoxyl groups (on the middle ring), was successfully synthesized via Horner-Wadsworth-Emmons (HWE) olefination and Sonogashira coupling reaction. Moreover, different molar ratios of light-emitting H-acceptor monomer PBB (M1) and hole-transporting monomer CAZ (M2) bearing a carbazole unit were copolymerized through free radical polymerization to obtain lightemitting and hole-transporting H-acceptor copolymers (P1-P5). H-acceptor copolymers P3 and P4 were complexed with different generations of dendritic H-donors (G1COOH-G3COOH) bearing 1,3,4-oxadiazole (OXD) dendrons and terminal benzoic acids via H-bonded self-assembly to form supramolecular side-chain copolymers (i.e., H-bonded dendritic complexes). In contrast to H-acceptor homopolymer P1 (HPBB), H-acceptor copolymers P2-P4 incorporated with carbazole (CAZ) moieties effectively enhance the glass transition temperatures (T g s) and minimize the interchain interations of the light-emitting H-acceptor units, and similar effects occur in their H-bonded dendritic complexes. In addition, red shifts of photoluminescence (PL) emissions in H-bonded dendritic complexes can be tuned up to 61 nm. Furthermore, H-bonded dendritic complexes excited at 305 nm of OXD absorption can create a stronger fluorescence than that excited at 397 nm of PBB absorption, indicating that the intensity of the sensitized emission of PBB (by energy transfer from OXD absorption at 305 nm) is even stronger than that of a direct emission of PBB (by merely PBB absorption at 397 nm). The OXD dendritic wedges in H-bonded dendritic complexes can lower the LUMO energy levels and provide a better electron injection property. H-acceptor polymer P4 and its H-bonded dendritic complexes showed electroluminescence (EL) emissions in the range of 464-519 nm from blue to green. In addition, a PLED device containing H-bonded dendritic complex P4/G1COOH showed an EL emission of 519 nm under a turn-on voltage of 6.5 V, with a maximum luminance of 408 cd/m 2 at 18 V and a luminance efficiency of 0.39 cd/A at 100 mA/cm 2 , respectively.
The inclusion of guanosine-5'-monothiophosphate (GMPS) in an in vitro transcription reaction facilitates enzymatic synthesis of an RNA transcript with a monothiophosphate group at the 5' end. A kinetic study of the modification reactions that generate monothiophosphate disulfide linkages with either 5'-GMPS alone or 5'-GMPS-primed RNA as the substrate revealed that the second-order rate constants increased as the pH was decreased. For example, when the reaction pH was lowered from 8 to 4, the k2 value for the coupling reaction between N-(6-[biotinamido]hexyl)-3'-(2'-pyridyldithio)propionamide (biotin-HPDP) and GMPS increased 67-fold from 1.84 to 123 M(-1) x s(-1). In addition to discussing a possible mechanism for coupling reactions that involve GMPS and disulfides, we also indicate conditions that are likely to be optimal for modification of the nucleophilic sulfur in 5'-GMPS-primed RNAs.
Four series of compounds 11~50 containing terminal alicyclic rings such as cyclohexylmethyl, cyclopentylmethyl, cyclobutylmethyl, and cyclopropylmethyl rings were synthesized and their liquid crystal behavior studied. The ring size and the length of flexible alkoxy chain influence the phase formation in different ways. While the smaller ring and the shorter alkoxy chain tend to favor the formation of the N phase, the larger ring and the longer alkoxy chain tend to favor the formation of the SmC phase. All the compounds except 11 and 21 exhibit SmA phases. The widest temperature range of the N, SmA, and SmC phases are found in the compounds 41, 46, and 20, respectively, which are 75 o C for 41, 115 o C for 46, and 100 o C for 20.
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