Graphene oxide (GO) with unique physical and chemical properties, such as high specific surface area, chemical stability and environmental friendliness, has been considered as an excellent adsorbent to remove organic dyes from polluted water. However, because of the electrostatic repulsion between the GO and anionic dyes, the adsorption capacity for anionic dyes is undesirable. Here photoreduced GO (PRGO) was prepared by solar light irradiation and used to investigate the adsorption capacity for anionic dyes. The obtained GO and PRGO were characterized by UV-visible absorption, Raman spectroscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). The adsorption kinetics and isotherms were evaluated through adsorption experiments of the anionic orange II (OII) dye adsorbed on GO or PRGO. The results revealed that the adsorption was an exothermic process and followed pseudo-second order kinetics. Four more typical anionic dyes, methyl orange (MO), Ponceau S (PS), Azo Rubine (AR), and Trypan Blue (TB), were also used to compare the adsorption capacities between GO and PRGO. It was demonstrated that the adsorption capacity of anionic dyes was significantly enhanced by PRGO, and the maximum enhancement was up to 8 fold. In conclusion, PRGO reduction by solar light irradiation in a green, convenient and cost effective manner, offers promise for the high-efficiency removal of anionic dyes in water treatment.

Photoreduction of graphene oxide is a flexible and green method to produce high-quality large-scale reduced graphene oxide. However, the dynamics of photoreduction of monolayer graphene oxide on the substrate, which plays a key role in practical applications, is still unclear. Here we perform fluorescence lifetime measurements to develop and understand this process by using time-correlated single photon counting technology. Two fluorescence lifetime components have been determined to reveal the dynamics and structural evolutions of graphene oxide during laser irradiation. The component with shorter lifetime, the fluorescence intensity of which is barely dependent on the laser irradiation, is assigned to confined sp2 clusters. The component with longer lifetime that is strongly sensitive to the irradiation time is attributed to hydroxyl groups. The present study offers a useful guidance for optoelectronic devices based on monolayer reduced graphene oxide.

We report that by applying an electric field to a single squaraine-derived rotaxane (SR) molecule on bare glass, the fluorescence can be completely quenched. The molecule undergoes a reversible fluorescence switch between a zero-field “on” state and a high-field “off” state, which is attributed to intramolecular electron transfer within the SR molecule.

The recent boom in sensor and optical materials based on graphene oxide (GO) requires the improvement and control of its optoelectronic properties. Here, we report the imaging and spectrum of transmission and fluorescence for monolayer graphene oxide (mGO) in an external electric field. It is demonstrated that the image of mGO reveals pronounced spatial heterogeneity under an electric field, and the spectrum presents electrically reversible modulated features. We explain these phenomena by the electric-field-induced changes of electronic density of localized states (DOLS), and we perform the calculations for DOLS by using the first-principles density functional theory.

Interfacial electron transfer (IET) dynamics in a 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindodicarbocyanine (DiD) dye molecule/indium tin oxide (ITO) film system have been probed at the ensemble and single-molecule levels. By comparing the difference in the external electric current (EEC) dependence of the fluorescence intensities and lifetimes of the ensembles and single molecules, it is shown that the single-molecule probe can effectively demonstrate IET dynamics. The backward electron transfer and electron transfer from the ground state induce single-molecule fluorescence quenching when an EEC is applied to the DiD/ITO film system.

The polymer glass surface can be many orders of magnitude more mobile than the interior. We probe dynamics with reorientation of single dye molecules spin-coated onto polymer films. Rotation jumps in transition dipole orientation are observed for approximately 30% of all single molecules. It is found for the first time that there are mainly three typical jumping patterns of orientation: dithering jump, alternate jump and stepping jump patterns. The distribution of rotational correlation time are used to characterize the dynamics of polymer glass surfaces.

Highly sensitive photoassociation spectroscopy is reported using the modulation technique in a Cs atom magneto-optical trap. Spectral data are extended to red detunings of 70 cm−1 below the Cs 6S1/2 + 6P3/2 dissociation limit. Long vibrational progressions are assigned to the 0u+ and 1g long-range molecular excited states. Some low-lying vibrational levels are first observed for the 0u+ and 1g states. By fitting the experimental data using the semiclassical LeRoy–Bernstein equation, the long-range molecular coefficients C3 of the 0u+ and 1g states are obtained. The present C3 values are closest to the theoretical values compared with the experimental results reported in earlier publications. Empirical potential curves in the long-range region are derived from these data.

Interfacial electron transfer (IET) dynamics in a 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindodicarbocyanine (DiD) dye molecule/indium tin oxide (ITO) film system have been probed at the ensemble and single-molecule levels. By comparing the difference in the external electric current (EEC) dependence of the fluorescence intensities and lifetimes of the ensembles and single molecules, it is shown that the single-molecule probe can effectively demonstrate IET dynamics. The backward electron transfer and electron transfer from the ground state induce single-molecule fluorescence quenching when an EEC is applied to the DiD/ITO film system.

The polymer glass surface can be many orders of magnitude more mobile than the interior. We probe dynamics with reorientation of single dye molecules spin-coated onto polymer films. Rotation jumps in transition dipole orientation are observed for approximately 30% of all single molecules. It is found for the first time that there are mainly three typical jumping patterns of orientation: dithering jump, alternate jump and stepping jump patterns. The distribution of rotational correlation time are used to characterize the dynamics of polymer glass surfaces.

We report that by applying an electric field to a single squaraine-derived rotaxane (SR) molecule on bare glass, the fluorescence can be completely quenched. The molecule undergoes a reversible fluorescence switch between a zero-field “on” state and a high-field “off” state, which is attributed to intramolecular electron transfer within the SR molecule.