This Account presents recent advances in understanding how and why dilute solutions/sols of low-molecular-mass organic gelators (LMOGs) undergo microscopic phase separation to form self-assembled fibrillar networks in molecular organogels. Concepts are illustrated structurally at the subnanometer (molecular) to several millimeter (bulk) length scales and dynamically over time scales that follow the assembly of supersaturated solutions/sols into gel phases. Examples include both structurally complicated (ALSmolecules with aromatic, linking, and steroidal groups) and simple (n-alkanes or n-alkanes along whose chains a hetero-group has been inserted) LMOGs in a wide range of organic liquids.

Thirteen members of a new class of low molecular-mass organogelators (LMOGs), amides, and amines based on (R)-12-hydroxystearic acid (HSA; i.e., (R)-12-hydroxyoctadecanoic acid) and the properties of their gels have been investigated by a variety of structural and thermal techniques. The abilities of these LMOGs, molecules with primary and secondary amide and amine groups and the ammonium carbamate salt of 1-aminooctadecan-12-ol, to gelate a wide range of organic liquids have been ascertained. Their gelating efficiencies are compared with those of HSA and the corresponding nitrogen-containing molecules derived from stearic acid (i.e., HSA that lacks a 12-hydroxyl group). Several of the HSA-derived molecules are exceedingly efficient LMOGs, with much less than 1 wt % being necessary to gelate several organic liquids at room temperature. Generally, the self-assembled fibrillar networks of the gels consist of spherulitic objects whose dimensions depend on the protocol employed to cool the precursor sol phases. X-ray studies indicate that the LMOG molecules are packed in lamellae within the fibers that constitute the spherulites. In addition, some of the organogels exhibit unusual thixotropic properties: they recover a large part of their viscoelasticity within seconds of being destroyed by excessive strain shearing. This recovery is at least an order of magnitude faster than for any other organogel with a crystalline fibrillar network reported to date. Correlations of these LMOG structures (as well as with those that lack a hydroxyl group along the n-alkyl chain, a headgroup at its end, or both) with the properties of their gels, coupled with the unusual theological properties of these systems, point to new directions for designing LMOGs and organogels.

Ž. Ž. Dual fluorescence and fast intramolecular charge transfer ICT is observed with 4-diisopropylamino benzonitrile Ž. Ž. DIABN in alkane solvents. The rate constant k for the reaction from the locally excited LE to the ICT state has a value a of 3.4 = 10 11 s y1 in n-hexane at 258C, with an activation energy E of 6 kJ mol y1. Efficient intersystem crossing with a a Ž. yield of 0.94 takes place from the ICT state. With 4-dimethylamino benzonitrile, in contrast, dual fluorescence is not Ž. observed in alkanes. The charge transfer reaction of DIABN is mainly favoured by its small energy gap D E S ,S , in

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A self-assembled photoactive antenna system containing a gold nanoparticle as the central nanocore and appended fullerene moieties as the photoreceptive hydrophobic shell is designed by functionalizing a gold nanoparticle with a thiol derivative of fullerene. Upon suspension of fullerene-functionalized gold nanoparticles (Au−S−C 60 ) in toluene we observe formation of 5−30 nm diameter clusters. The ease of suspending these nanoassemblies in organic solvents allows us to probe the excited state interactions by spectroscopic methods. The quenching of fluorescence emission as well as decreased yields of triplet excited state suggest the participation of excited singlet in the energy transfer to the gold nanocore. Application of electrophoretically deposited Au−S−C 60 nanoassemblies on optically transparent electrodes in the photoelectrochemical conversion of light energy has been demonstrated. Introduction.Advances in the field of nanotechnology provide an alternate "bottom-up" approach, in which the nanoparticles and bridging molecular units are assembled together as circuits in nanoelectronics. [1][2][3] Such arrangements can lead to the design of optoelectronic nanodevices, which can perform specific functions such as light-induced energy and electron-transfer processes.The metal and semiconductor nanoparticles possess size dependent optical, electronic, and catalytic properties and their synthesis and characterization are well documented. [4][5][6][7][8][9][10] Recently, attention has been drawn toward capping of metal nanoparticles with photoactive ligands using functional groups such as thiols, amines, and isothiocynates. [11][12][13][14][15][16][17][18][19][20][21] Elucidation of photoinduced energy and electron-transfer processes in fluorophore-metal nanoparticles are important in understanding the photochemical behavior of molecules bound to metal nanoparticles. In addition, the construction of two-and three-dimensional nanoassemblies of photoactive molecules with colloidal metal particles are useful for improving photoinduced charge separation and developing sensors for biological applications. [22][23][24][25][26][27]