Two new donor–acceptor (D–A) alternative copolymers, PBDTDTQx-T and PBDTDTQx-O, were designed and synthesized to investigate the influence of two-dimensional conjugated structure on photovoltaic properties of conjugated polymers. In these two polymers, PBDTDTQx-O was used as control material, which is an alternative copolymer based on a quinoxaline derivative (DTQx) and alkoxy-substituted benzo[1,2-b:4,5-b′]dithiophene (BDT-O) unit; PBDTDTQx-T has an identical conjugated backbone as PBDTDTQx-O, but a simple two-dimensional conjugated BDT unit (BDT-T) was used to replace the alkoxy-BDT. The polymers were characterized by TGA, UV–vis absorption, electrochemical cyclic voltammetry, hole mobility of space-charge-limited current (SCLC) model, and photovoltaic measurements. It was found that PBDTDTQx-T exhibits similar molecular energy levels and higher hole mobility than PBDTDTQx-O. The power conversion efficiency (PCE) of the polymer solar cells (PSCs) based on PBDTDTQx-T: [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM) = 1/2 (w/w) reached ∼5%, which is 60% higher than that of PBDTDTQx-O-based PSC. On the basis of these results, it can be concluded that the application of two-dimensional conjugated structure would be a feasible approach to improve photovoltaic properties of conjugated polymers.

We carried out femtosecond magic-angle and polarized pump–probe spectroscopies for the light-harvesting complex 2 (LH2) from Thermochromatium (Tch.) tepidum in aqueous phase and in chromatophores. To examine the effects of LH2 aggregation on the dynamics of excitation energy transfer, dominant monodispersed and aggregated LH2s were prepared by controlling the surfactant concentrations. The aqueous preparations solubilized with different concentrations of n-dodecyl-β-d-maltoside (DDM) show similar visible-to-near-infrared absorption spectra, but distinctively different aggregation states, as revealed by using dynamic light scattering. The B800 → B850 intra-LH2 energy transfer time was determined to be 1.3 ps for isolated LH2, which, upon aggregation in aqueous phase or clustering in chromatophores, shortened to 1.1 or 0.9 ps, respectively. The light-harvesting complex 1 (LH1) of this thermophilic purple sulfur bacterium contains bacteriochlorophyll a absorbing at 915 nm (B915), and the LH2(B850) → LH1(B915) intercomplex transfer time in chromatophores was found to be 6.6 ps. For chromatophores, a depolarization time of 21 ps was derived from the anisotropy kinetics of B850*, which is attributed to the migration of B850* excitation before being trapped by LH1. In addition, the B850* annihilation is accelerated upon LH2 aggregation in aqueous phase, but it is much less severe upon LH2 clustering in the intracytoplasmic membrane. These results are helpful in understanding the light-harvesting function of a bacterial photosynthetic membrane incorporating different types of antenna complexes.

We report a novel molecular dyad as an antioxidant, retinylisoflavonoid, with a retinal analogue C22-aldehyde and the isoflavonoid daidzein covalently linked. Its physicochemical properties, pKa (pKa1 = 8.45, pKa2 = 11.42), oxidation potential (1.03 V vs NHE), and Log10 partition (Log P = 1.96), as well as the Trolox equivalent antioxidant capacity (TEAC = 0.4), have been characterized. Spectroscopic and quantum chemical investigations have revealed the following unique structural characters: (i) Either free in solution or included in liposomal membranes, the C22-aldehyde moiety of retinylisoflavonoid is coplanar with the B-ring of daidzein owing to the strong intramolecular hydrogen bonding C14′═O···HO−B4′. Accordingly, the C22-aldehyde moiety extends its π-conjugation significantly to the B-ring. (ii) The inherent amphiphilicity of retinylisoflavonoid allows the C22-aldehyde moiety embedded in the lipid phase of the liposomes, whereas the daidzein counterpart stays at the membrane surface, in effect facilitating interior-to-surface radical communication. As the result, the antilipooxidation activity of retinylisoflavonoid is improved significantly in protecting membrane lipids compared to the parent compounds alone or in combination, and importantly, the performance is more prominent under higher-level oxidative stress. This work provides an advanced case study of new antioxidant development based on optimized electronic and molecular structures.

We have performed systematic spectroscopic titrations to characterize the binding reaction of cationic meso-tetrakis(4-(N-methylpyridiumyl))porphyrin (TMPyP4) with the G-quadruplex (G4) of human telomeric single-strand oligonucleotide d[TAGGG(TTAGGG)3T] (S24), for which special effort was made to examine the TMPyP4-G4 binding stoichiometry, the binding modes, and the conformational conversion of the G4 structure under different potassium ion (K+) concentration. It is found that, in the presence of 0, 10 mM, and 100 mM K+, TMPyP4 forms a complex with the anti-parallel G4 in a TMPyP4-to-G4 molar ratio of 5, 5 and 3, respectively, and the increase of K+ concentration would reduce the binding affinity of TMPyP4 to G4. For the TMPyP4–G4 complex, the end-stacking mode and groove binding mode were presumed mainly by the results of time-resolved fluorescence spectroscopy in the three cases. Most importantly, it is found that TMPyP4 can directly induce the formation of the anti-parallel G4 structure from the single-strand oligonucleotide S24 in the absence of K+, and that it can preferentially induce the conformational conversion of the G4 structure from the hybrid-type to the anti-parallel one in the presence of K+.