A series of substituted 12‐sulfonium zwitterions 1[n] and one example of a 1‐sulfonium analogue 2[5]a were prepared in four steps. Derivatives 1[n] exhibit rich crystalline polymorphism and a high‐temperature SmBcry phase stabilized by dipolar interactions. Solution studies in a nematic host demonstrated positive dielectric anisotropy of compounds 1[5]a–1[5]c (Δε ≈ +18 extrapolated from 8 mol‐% solutions) resulting from a longitudinal electric dipole moment of ca. 9.5 D. The effectiveness of additives 1[5] was analyzed by using the Maier–Meier formalism and DFT methods and compared to those of more polar derivatives 3[6]a and Pyr[10].

Intramolecular electronic interactions were investigated in five series of 12-, 10-, and 6-vertex closo-boranes and hydrocarbons (benzene, acetylene, bicyclo[2.2.2]octane, and cubane) substituted with triple-bonded groups Y≡Z (C≡CR, C≡N, C≡O, and N≡N). Structural data (single crystal X-ray crystallography), spectroscopic properties (UV, IR, and NMR), chemical behavior (dediazoniation reactions), and electronic structure calculations (hybridization and π bond order) are all in agreement that the degree of electronic conjugation between the cluster and the Y≡Z substituent is lowest for the 12-vertex closo-borane and highest for the 6-vertex analog.

Herein we demonstrate the use of a novel dimerization-based molecular beacon (MB) probe consisting of two metallo-phthalocyanine (Pc) fluorophores that use near-IR fluorescence, appropriate for highly specific and sensitive in-vivo and/or in-vitro DNA/RNA detection. Pc's possess a propensity to form non-fluorescent H-dimers that is utilized as the molecular "off" switch in the closed MB conformation. The "on" switch, which is generated when the solution target binds to the loop of the MB forming the open form, also provides two fluorophores for transduction resulting in a doubling of the extinction coefficient and improving the resulting fluorescence yield compared to a classical single-fluorophore/quencher MB system. In addition, the Pc-based MBs possess high thermal, photo and chemical stabilities that are essential for many highly sensitive applications, such as molecular imaging. The dimer-based MBs were obtained using a simple singlestep synthesis procedure and demonstrated excellent quenching efficiencies (98%) as well as a high signal-to-background ratio (~60) exceeding the performance characteristics of many conventionallyavailable MB probes.Since their 1996 inception by Tyagi and Kramer, 1 molecular beacons (MBs) have become powerful tools for a variety of applications in DNA/RNA detection (e.g. real-time PCR, SNP detection, in vivo cellular imaging, cancer imaging etc.). MB-based detection systems are separation-free and highly specific however, their sensitivity (defined as the ratio of the fluorescence in the open versus closed form; signal-to-background, SB) is limited due to incomplete quenching of the closed form while signal in an open form is confined to one fluorophore. Various approaches for SB enhancement have been pursued including introduction of multiple fluorophores and/or quenchers, 2 eximer emission, 3, 4 FRET, 5 conjugated-polymers, 6 electrochemiluminescence 7 or quantum-dots. 8 The quest for more sensitive probes is still necessary along with the need to increase the MB reporting fluorophore's photostability to prolong observation times in imaging applications and conducting assays in the near-IR, where significant autofluorescence can be avoided. 9Water soluble metallo-phthalocyanines (Pc's) are near-IR fluorophores that possess high extinction coefficients, favorable quantum yields, narrow absorption/emission envelopes and display extraordinarily high photostabilities. 10, 11 These qualities make Pc's particularly attractive for MB applications along with other unique characteristics, such as: (i) Intrinsic propensity to form non-fluorescent H-type dimers that can be utilized as a molecular "off" switch for the closed MB form while two flourophores instead of one would be available for readout in the open form; (ii) diminished Pc dimerization when it is part of a relatively large oligonucleotide construct (e.g. MB hybridized to a complementary target as has been demonstrated by us), but the lack of fluorescence when bound to a relatively short DNA E-mail: chsope@lsu.edu. co...