Efficient Emission of Ultraviolet Light by Solid State Organic Fluorophores: Synthesis and Characterization of 1,4-Dialkeny-2,5-dioxybenzenes.

The design and development of organic luminophores that exhibit efficient ultraviolet (UV) fluorescence in the solid state remains underexplored. Here, we report that 1,4-dialkenyl-2,5-dialkoxybenzenes and 1,4-dialkenyl-2,5-disiloxybenzenes act as such UV-emissive fluorophores. The dialkenyldioxybenzenes were readily prepared in three steps from 2,5-dimethoxy-1,4-diacetylbenzene or 2,5-dimethoxy-1,4-diformylbenzene via two to four steps from 1,4-bis(diethoxyphosphonylmethyl)-2,5-dimethoxybenzene. The dialkenyldioxybenzenes emit UV light in solution (λem =350-387 nm) and in the solid state (λem =328-388 nm). In addition, the quantum yields in the solid state were generally higher than those in solution. In particular, the adamantylidene-substituted benzenes fluoresced in the UV region with high quantum yields (Φ=0.37-0.55) in the solid state. Thin films of poly(methyl methacrylate) doped with the adamantylidene-substituted benzenes also exhibited UV emission with good efficiency (Φ=0.27-0.45). Density functional theory calculations revealed that the optical excitation of the dialkenyldimethoxybenzenes involves intramolecular charge-transfer from the ether oxygen atoms to the twisted alkenyl-benzene-alkenyl moiety, whereas the dialkenylbis(triphenylsiloxy)benzenes were optically excited through intramolecular charge-transfer from the oxygen atoms and twisted π-system to the phenyl-Si moieties of each triphenylsilyl group.

Unidirectional growth of heavy meromyosin clusters along actin filaments revealed by real-time fluorescence microscopy.

Heavy meromyosin (HMM) forms clusters along actin filaments under low ATP concentrations. Here, we observed the growth of HMM clusters under low concentrations of ATP in real time using fluorescence microscopy. When actin filaments were loosely immobilized on positively charged lipid bilayers, clusters of HMM-GFP were readily formed. Time-lapse observation revealed that the clusters grew unidirectionally. When we used a mixture of actin filaments and copolymers of actin and acto-S1dC, a chimeric protein of actin and the myosin motor domain, HMM-GFP preferentially formed clusters along the copolymers. We thus suggest that binding of myosin motors carrying ADP and Pi induces unidirectional conformational changes in actin filaments and allosterically recruits more myosin binding. In contrast, when actin filaments and copolymers were anchored to glass substrate via stable biotin-avidin linkage, higher concentrations of HMM-GFP were required to form clusters than on the lipid bilayer. Moreover, actin filaments and copolymers were not discriminated regarding preferential cluster formation. This is presumably because the myosin-induced cooperative conformational changes in actin filaments involve changes in the helical twist. Consistent with this, cofilin clusters, which supertwist the helix, were readily formed along loosely immobilized actin filaments, but not along those anchored via biotin-avidin linkage.