Fluorescent DNA-labeling cassettes are designed to have a common absorbing chromophore matched to a single exciting laser wavelength, but up to four different emitters. Experiments reported here have examined the energy-transfer rates and fluorescence polarization characteristics for two different types of cassette, involving three distinct relative orientations of the donor and acceptor transition moments and the axis of the rigid linker. Energy-transfer times range from <200 fs to approximately 20 ps, the fastest transfer times occurring when the transition moments of the donor and acceptor species are aligned parallel to the linker axis. Experimental evidence is presented that supports a through-bond energy-transfer mechanism, in contrast with a commercial DNA-labeling agent, which exhibits much slower transfer times controlled by FRET. These rigid cassettes also exhibit polarized fluorescence from the acceptor species, so that this particular type of DNA-labeling probe has some of the advantages of single-molecule probes such as rhodamine and coumarin dyes.
A novel polymer P-1 is prepared by the reaction of the monomer 5,5'-divinyl-2,2'-bipyridine and Salen-Zn(II) via Heck cross coupling. Interestingly, P-1 can further incorporate with Eu(TTA)(3)·2H(2)O to generate copolymer P-2 with two different metal centers. P-2 exhibits exceptional dual emissive properties which can be tuned by excitation wavelength. For example, an orange fluorescence can be obtained when P-2 is excited at 430 nm, whereas a red emission with a huge Stoke shift of 57 nm is observed when it is excited at 345 nm. The high wavelength emission can be attributed to Eu(III) ((5)D(0)→(7)F(2) ), which is lit by an effective photoinduced energy transfer process between P-1 and the Eu(TTA)(3) complex. The properties of P-2 have led to a better understanding of the energy transfer process between P-1 and Eu(TTA)(3) moieties.
A novel fluorescence chemosensor 1 based on (R)‐binaphthyl‐salen can exhibit highly sensitive and selective recognition responses toward Cu2+ by "turn‐off" fluorescence quench type in THF/H2O, and Zn2+ by "turn‐on" fluorescence enhancement type in CHCl3/CH3CN, respectively, suggesting that solvents can dramatically affect the responsive properties of salen‐based chemosensor. In addition, Cu2+ can lead to the most pronounced changes of CD spectra without the influence of solvents, which indicates this kind chemosensor can also be used as a sole Cu2+ probe based on CD spectra.
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