Interfacial properties of hybrid nanomaterials

A brief summary of our ongoing efforts to understand the surface properties of nanoparticles using fluorophores, namely pyrene alkanethiols, is presented. Excited state interactions were investigated by varying the length of the spacer group and the concentration of fluorophore. The flexible long alkyl chain tethering pyrene in Au-P2/Au-P3 allows free interaction between fluorophores resulting in excimer formation whereas the intermolecular interactions are limited in the Au-P1 system due to the restriction imposed by the curvature of spherical gold nanoparticle. A gradual increase in the peak intensity ratio of III/I band of the normal fluorescence of pyrene was observed indicating that the surface of nanoparticle is more polar than the bulk solvent (toluene)

Supramolecular Organization of Metal Nanoparticles in Solution and of Phenyleneethynylenes on Surfaces

Most of the procedures reported for the synthesis of metal nanoparticles involve the use of strong reducing agents or elevated temperatures. This limits the possibility of developing metal nanoparticle based sensors for the in situ detection of analytes. One of the objectives of the present investigations is to (i) develop newer methodologies for the synthesis of metal nanoparticles in aqueous medium at ambient conditions and (ii) their use in the detection of metal cations by taking advantage of the unique coordination ability. Ideally, biocompatible molecules which possess both the reducing and stabilizing groups are desirable for such applications. Formation of stable supramolecular assembly, by bringing metal nanoparticles close to each other, results in plasmon coupling and this strategy can be effectively utilized for the development of metal nanoparticle based sensors.Another objective of the present study is to understand the supramolecular organization of molecules on surfaces. Various noncovalent interactions between the molecules and with surface play a decisive role in their organizations. An in-depth understanding of these interactions is essential for device fabrications. Recent photophysical studies have revealed that phenyleneethynylene based molecular systems are ideal for device application. The second objective of the thesis focuses on understanding the (i) organization of phenyleneethynylenes on highly oriented pyrolytic graphite (HOPG) surface with atomic level precision and (ii) weak intermolecular interactions which drive their organization

1,10-Phenanthrolines: Versatile building blocks for luminescent molecules, materials and metal complexes

1,10-Phenanthroline entails several appealing structural and chemical properties: rigidity, planarity, aromaticity, basicity, chelating capability. This makes it a versatile starting material for synthetic organic, inorganic and supramolecular chemistry. In this tutorial review we examine how the chemical versatility of pristine 1,10-phenanthroline, a weakly fluorescent molecule, has been exploited to design many UV-Vis-NIR luminescent organic derivatives and coordination compounds with transition-metal (Ru(ii), Os(ii), Rh(iii), Cr(iii), Pt(ii), Zn(ii), Cu(i), Ag(i)) and rare-earth (Eu(iii), Tb(iii), Yb(iii), Nd(iii), Er(iii)) cations. They are utilized for many analytical and technological applications. © 2009 The Royal Society of Chemistry

Engineering spherical nanostructures through hydrogen bonds

Chromophoric acetylenic scaffolds bearing complementary uracyl and 2,6-di(acetylamino) pyridyl moieties undergo supramolecular recognition and generate uniform nanoparticles, as observed by UV-Vis, AFM and TEM measurements

Engineering supramolecular photoactive nanomaterials by hydrogen-bonding interactions

The photophysical properties of molecules containing anthracene, pyrene, or phenyleneethynylene chromophores bearing complementary triple H-bonding terminal units, namely, 2,6-di(acetylamino) pyridine (donor-acceptor-donor, DAD) and uracyl (acceptor-donor-acceptor, ADA) have been investigated as a function of solvent polarity. For asymmetric systems, presenting only one H-bonding unit, a solvatochromic effect is found, suggesting a charge-transfer character of the lowest electronic excited state. Systematic absorption and emission studies carried out as a function of temperature show that phenyleneethynylenes having linear geometry and H-bonding functionalities at both ends undergo reversible self-aggregation in cyclohexane (CHX), leading to the formation of spherical nanoparticles, as evidenced by wide-field fluorescence microscopy (WFM), atomic force microscopy (AFM), and transmission electron microscopy (TEM). A combination of an anthracene derivative bearing only one ADA terminal functionality and a linear phenyleneethynylene derivative possessing two DAD terminal groups in CHX (2: 1 molecular ratio) leads to the formation of vesicular nanostructures. The interaction of linear phenyleneethynylenes possessing two terminal 2,6-di(acetylamino) pyridine functionalities with that bearing bis uracylic units gives origin to nanofibers, while the assembly of the former with bisuracylic units exhibiting bent geometry leads to the formation of helical nanofibers. The length of these fibers can be controlled by addition of the anthracene derivative having only one uracyl group which effectively blocks the extent of H-bonding, prompting the formation of shorter nanorods

Self-organization of phenyleneethynylene into wire-like molecular materials on surfaces

A model phenyleneethynylene, which does not possess any functional groups, self-organizes into wire-like structures on 2D surfaces. High-resolution STM imaging revealed that the molecules are arranged in a skewed 1D fashion. Analysis of various domains indicated the existence of two types of molecular packing arising from different modes of alkyl CH···π interaction, which was further supported by theoretical calculations