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The photophysics of dialkylamino- and/or pyridine-containing functional chromophores, 1,4-distyryl-2,5-bis(ethynylaryl)benzenes (cruciforms) was investigated; their fluorescence quantum yields and emissive lifetimes were determined. Depending upon their substituents, the frontier molecular orbitals (FMOs) of these cruciforms are either congruent, i.e., HOMO and LUMO occupy the same real space, or disjoint, i.e., the HOMO is located on one branch of the cruciform while the LUMO is located on the second one. Donor-acceptor substitution leads to a disjoint FMO pattern, while the parent 1,4-distyryl-2,5-bis(phenylethynyl)-benzene shows congruent FMOs. The photophysics of the cruciforms was investigated upon addition of either an excess of trifluoroacetic acid or an excess of selected metal (Mg2+, Ca2+, Mn2+, Zn2+) trifluoromethanesulfonate salts. Addition of either metal ions or protons led to analogous but not identical changes in the spectroscopic properties of the investigated cruciforms. The collected data suggest that the metals bind preferentially at the aniline nitrogen and not at the electron-rich arene. The spatially separated FMOs permit the independent manipulation of the HOMO and the LUMO of such cruciforms. If the branches contain metal-complexing moieties, metal binding leads to either a hypsochromic or a bathochromic shift in emission via interaction of the metal cations with either the HOMO or the LUMO. [ABSTRACT FROM AUTHOR]

The article focuses on the study which explores the quenching properties of fluorophores assembled on a DNA backbone. According to the study, the DNA-like fluorophores as a new class of reporters and sensors which display highly diverse and tunable properties. A simple oligomer series has been constructed containing pyrene nucleoside monomers to explore the chain length on the optical properties. Information about the details of the procedure and its results is discussed.

The article presents an abstract "Reduced Fluorescence Quenching of Cyclodextrin—Acetylene Dye Rotaxanes," by Jong S. Park, James N. Wilson, Kenneth I. Hardcastle, Uwe H. F. Bunz, and Mohan Srinivasarao.

The article analyzes switching of intramolecular charge transfer in cruciforms with respect to metal ion sensing. In most, but not all, chromophores, HOMO and LUMO are spatially superimposed. However, adding donor and/or acceptor substituents to cross-shaped chromophores at suitable positions can lead to independent electronic shifts in HOMO and LUMO into opposite directions. In the cruciforms 2-4, the HOMO is located on the distyrylbenzene branch, while the LUMO is situated on the bisarylethynyl axis of the molecule. As a consequence, the intramolecular charge-transfer emission and absorption of such cruciforms is dependent upon solvent polarity. It demonstrates dramatic blue and/or red shifts of emission and absorption upon coordination of metal cations to cruciforms.

This article reports that gold nanorods, surface-functionalized with biotin, can be assembled preferentially in an end-to-end fashion upon the addition of a streptavidin linker. Commercially available biotin disulfide, EZ-Link Biotin HPDP is also applied. Other groups have used biotin-streptavidin linkers to assemble inorganic nanospheres into three-dimensional (3D) structures, and Mann's group has shown that gold nanorods coated with DNA can be similarly assembled into 3D aggregates by the addition of a complementary linker DNA. Results of the article suggest that chemical linkages can organize nanorods in a nonrandom fashion, which may be exploited for the assembly of higher-order arrays of nanomaterials.

Investigates the chiroptical properties of p-phenyleneethynylene copolymers in thin films. Decline of circularly polarized photoluminescence signal; Presentation of the dark-field micrograph of thin polymer; Increase of dimethyloctyl side chains in copolymers.

The article describes arrays of self-assembled picoliter holes fabricated from poly(para-phenyleneethynylene). These holes are formed by heating self-assembled bubble arrays to 300 degree Celsius. Picoliter beakers allow isolating very small volumes of liquid or single cells and interrogating them by either electrochemical or enzymatic methods. However, the fabrication of picoliter beakers or picoliter vials is not trivial and often involves tedious photolithographic methods that are expensive and not commonly available to chemists. It was therefore of fundamental and practical interest to develop a simple nonphotolithographic access to picoliter vials.

A new optical strategy to determine the binding modes (intercalation vs groove binding) of small fluorescent organic molecules with calf thymus DNA was developed using two-photon absorption (TPA) spectroscopy. Two-photon excited emission was utilized to investigate a series of fluorescent nuclear dyes. The results show that TPA cross-sections are able to differentiate the fine details between the DNA binding modes. Groove binding molecules exhibit an enhanced TPA cross-section due to the DNA electric field induced enhancement of the transition dipole moment, while intercalative binding molecules exhibit a decrease in the TPA cross-section. Remarkably, the TPA cross-section of 4,6-bis(4-(4-methylpiperazin-1-yl)phenyl) pyrimidine is significantly enhanced (13.6-fold) upon binding with DNA. The sensitivity of our TPA methodology is compared to circular dichroism spectroscopy. TPA demonstrates superior sensitivity by more than an order of magnitude at low DNA concentrations. This methodology can be utilized to probe DNA interactions with other external molecules such as proteins, enzymes, and drugs. [ABSTRACT FROM AUTHOR]