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A simple ratiometric fluorescence probe based on vinylpyrrole end-capped bipyridine for the visual sensing of Zn2+ under aqueous physiological pH (6.8-7.4) is described. The fluorophores 3a-c showed strong emission around 537 nm in acetonitrile with a quantum yield of 0.4. In buffered (HEPES, pH 7.2) acetonitrile-water mixture (9:1 v/v), titration of transition metal salts to 3c showed strong quenching of the emission at 547 nm except in the case of Zn2+, which resulted in a red-shifted emission at 637 nm. Alkali and alkaline earth metal salts could not induce any considerable changes to the emission behavior of 3a-c. The binding of Zn2+ was highly selective in the presence of a variety of other metal ions. Though Cu2+ quenches the emission of 3c, in the presence of Zn2+, a red emission prevails, indicating the preference of 3c toward Zn2+. Job plot and Benesi-Hildebrand analysis revealed a 1:1 complexation between the probe and the metal ion. The selective visual sensing of Zn2+ with a red emission is ideally suited for the imaging of biological specimens.

Trithienylenevinylenes having amide end functional groups form supramolecular gels in nonpolar solvents, comprised of self-assembled nanowires. These gels exhibit the unique property of solution phase epitaxy leading to the alignment of fibers on mica surface. FP-TRMC studies revealed high charge carrier mobility for xerogels from decane-chloroform whereas films obtained from chloroform solutions showed less mobility, highlighting the role of self-assembly and gelation on the electronic properties of semiconducting molecular gelators. This study opens the window for a new class of conducting gelators which may find wide application in organic electronic devices.

Dedicated to the memory of Darshan RanganathanExcitation energy transfer within and between molecular systems plays an important role in natural processes, such as photosynthesis. In this context, there has been widespread interest in mimicking the mechanism of solar-energy harvesting of natural photosynthesis with the aid of synthetic molecular systems. Apart from this, photoinduced energy transfer has become significant in the area of photovoltaics, organic light-emitting diodes, fluorescent labeling, and in a variety of photonic devices. In most of these cases, energy transfer is considerably influenced by the supramolecular ordering and spatial relationship of the donor and acceptor chromophores. Molecular architectures such as hydrogen-bonded systems, [1] dendrimers, [2] chromophore-linked polymers, [3] Langmuir±Blodgett films, [4] and self-assembled monolayers [5] are of extremely important in this context. Among a plethora of donor±acceptor systems investigated, energy and electron transfer from oligo(phenylenevinylene)s (OPVs) and poly(phenylenevinylene)s (PPVs) to acceptors, such as C 60 , [6] phenanthroline, [7] and doped organic dyes [8] have generated enormous interest because of their potential use in photovoltaic and light-emitting devices. From this view point, the recent reports by Meijer and coworkers on energy and electron transfer from OPV-functionalized dendrimers and supramolecular assemblies to various acceptors are of particular interest. [9] This situation has prompted us to investigate on the potential of OPV based organogels for the purpose of energy transfer and light harvesting. [10] Small-molecule-based organogels have attracted much attention in recent years because of their interesting physical properties and architectural elegance. [11] However, organogels based on p-conjugated systems are relatively very few. [12] Recently, we have reported hydrogen-bond-and p-stackinduced supramolecular assembly of the OPV derivatives 1 a,b, which leads to the formation of entangled nanostructures, which induce gelation of hydrocarbon solvents. [13] The absorption and emission properties of 1 a,b showed dramatic changes during gelation, which is an indication of strong intermolecular p-electronic coupling of the ordered selfassembled OPV gel. Excitation of 1 a,b in cyclohexane at 380 and 470 nm revealed the emission corresponding to the monomeric species (l em ¼ 455 and 483 nm, F f ¼ 0.40 AE 0.01 related to quinine sulfate, t ¼ 1.46 ns; Figure 1, spectrum b) and self-assembled species (l em ¼ 525 and 565 nm, F f ¼ 0.40 AE 0.01 related to Rhodamine 6G, t ¼ 1.62 ns; Figure 1, spectrum c), which showed strong dependency on solvent polarity and temperature.Herein we describe an interesting case of a thermoreversible fluorescence-resonance energy transfer (FRET) and light harvesting, exclusively from OPV based supramolecular gel nanostructures of 1 a,b to an organic dye. To study the feasibility of such an energy transfer, we chose Rhodamine B as the acceptor, the absorption (l max ¼ 555 nm...

Oligo(thienylenevinylene) (OTV) based gelators with high conductivity are reported. When compared to OTV1, OTV2 having an increased conjugation length forms relatively strong gels with a metallic conductivity of 4.8 S/cm upon doping which is the highest value reported for an organogelator. This new class of conducting gels is expected to be useful for organic electronics and photonics application, particularly for bulk heterojunction devices.

This article describes the recent progress made to the understanding of the excited state interactions in organogels derived from linear π-conjugated molecules. The soft organogel scaffolds of such systems create an excellent ambience for the self-organization of the molecules allowing the modulation of their excited state properties and thereby opening a new world of fascinating materials with interesting physical properties at nano- and macroscopic levels. Noncovalent interactions provide opportunity for the molecules to interact electronically within a space of defined size and shape. As a result, the photophysical properties of the molecules in solution and gel states are different from each other. In this perspective article we analyze the role of the self-assembled organogel scaffolds of π-gels derived from linear π-systems in modulating the excited state properties such as excited state energy transfer, exciplex emission, phosphorescence, and aggregation-induced enhanced emission (AIEE), when compared to the corresponding individual molecules.

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This paper reports on experiments intended for investigating the feasibility of preparing hybrid thermoreversible gels from covalent polymers and noncovalent self-assembling pi-conjugated molecules. The formation and the degree of dispersion of these hybrid gels have been studied with polystyrenes of various tacticities and oligo(p-phenylenevinylene) molecules (OPV) in different nonpolar organic solvents. Detailed investigations of the systems have been carried out by DSC, SAXS, and AFM. It is shown that no liquid-liquid phase separation is involved, indicating that the systems are highly compatible, and that the growth of one type of gel does not interfere with the other. These studies reveal that the resultant hybrid gels are composed of the intermingled fibrillar architectures of both gels.