Light driven mesoscale assembly of a coordination polymeric gelator into flowers and stars with distinct properties

Control over the self-assembly process of porous organic–inorganic hybrids often leads to unprecedented polymorphism and properties. Herein we demonstrate how light can be a powerful tool to intervene in the kinetically controlled mesoscale self-assembly of a coordination polymeric gelator. Ultraviolet light induced coordination modulation via photoisomerisation of an azobenzene based dicarboxylate linker followed by aggregation mediated crystal growth resulted in two distinct morphological forms (flowers and stars), which show subtle differences in their physical properties

π-Organogels of self-assembled p-phenylenevinylenes: soft materials with distinct size, shape, and functions

This account is focused on the self-assembly of p-phenylenevinylenes, a linear π-system, which has been extensively studied over the years due to both fundamental and technological importance. A serendipitous observation of the gelation of an oligo(p-phenylenevinylene) (OPV) derivative in nonpolar hydrocarbon solvents that led to a new class of functional materials, namely, π-organogels, is described. Strategies to control the size, shape, and functions of the supramolecular architectures of OPV self-assemblies are highlighted. Formation of nano- to microsized helical architectures, control on chromophore packing, self-assembly induced modulation of optical properties, and application as light-harvesting assemblies are the important features of this novel class of photonically and electronically active soft materials

Organogels as scaffolds for excitation energy transfer and light harvesting

The elegance and efficiency by which nature harvests solar energy has been a source of inspiration for chemists to mimic such process with synthetic molecular and supramolecular systems. The insights gained over the years from these studies have contributed immensely to the development of advanced materials useful for organic based electronic and photonic devices. Energy transfer, being a key process in many of these devices, has been extensively studied in recent years. A major requirement for efficient energy transfer process is the proper arrangement of donors and acceptors in a few nanometers in length scale. A practical approach to this is the controlled self-assembly and gelation of chromophore based molecular systems. The present tutorial review describes the recent developments in the design of chromophore based organogels and their use as supramolecular scaffolds for excitation energy transfer studies

Noncovalent macromolecular architectures of oligo(p-phenylenevinylene)s (OPVs): role of end functional groups on the gelation of organic solvents

Self-assembly of a few OPV derivatives having different end functional groups to aggregates, fibrous networks and organogels are discussed. OPV1 and OPV2 functionalized with ester moieties form gels in nonpolar hydrocarbon solvents whereas OPV3 with carboxylic acid groups form gel from THF and dichloromethane. OPV4 with dicyano moieties form aggregates but could not gelate solvents. AFM and TEM studies revealed considerable difference in the morphology of the self-assembled structures of OPV1-4. From the optical, morphological and gelation data it is concluded that the nature of the end functional groups strongly influences upon the self-assembly and gelation properties of OPVs

Gelation-assisted light harvesting by selective energy transfer from an oligo(p-phenylenevinylene)-based self-assembly to an organic dye

Hot gels get turned off: Gelation of the title molecules facilitate transfer of excitation energy exclusively from the self-assembled nanostructures (see scheme path a) to Rhodamine B and not from the single molecules (path b), thereby establishing the role of self-assembled gel nanostructures in light harvesting. The emission from the dye can be shut off in a thermoreversible fashion since the self-assembly breaks to form molecular, dissolved oligo(phenylenevinylene)s above the gel melting temperature (T_gel)

RGB emission through controlled donor self-assembly and modulation of excitation energy transfer: a novel strategy to white-light-emitting organogels

A white-light-emitting organogel is designed by the controlled self-assembly of a bischolesterol-functionalized OPV donor that allows slow energy migration and partial energy transfer in the gel state to an encapsulated acceptor. The white-light emission occurs because of the combination of blue-light emission from the OPV monomers, green-light emission from the OPV self-assembly, and red-light emission from the acceptor

Evolution of nano- to microsized spherical assemblies of a short oligo(p-phenyleneethynylene) into superstructured organogels

Wires to particles: A subtle balance of H-bonding, π-stacking, and van der waals interactions facilitates the concentration-controlled self-assembly of a short molecular wire (see figure) into nanoparticles and fluorescent microspheres in nonpolar hydrocarbon solvents. Above a critical concentration, a blue-light emitting organogel is formed

Self-assembly of oligo(para-phenylenevinylene)s through arene - perfluoroarene interactions: π gels with longitudinally controlled fiber growth and supramolecular exciplex-mediated enhanced emission

The arene-perfluoroarene (ArH-ArF) interaction, which has been extensively studied in the field of solid-state chemistry, is exploited in the hierarchical self-assembly of oligo(para-phenylenevinylene)s (OPVs) with controlled longitudinal fiber growth that leads to gelation. The size of the self-assembled fibers of a pentafluorophenyl-functionalized OPV 5 could be controlled through C-F⋅⋅⋅H-C hydrogen bonding and π stacking. The ability of fluoroaromatic compounds to form excited-state complexes with aromatic amines has been utilized to form a supramolecular exciplex, exclusively in the gel state, that exhibits enhanced emission. Thus, the commonly encountered fluorescence quenching during the self-assembly of OPVs could be considerably prevented by exciplex formation with N,N-dimethylaniline (DMA), which only occurred for the fluorinated OPV and not for the non-fluorinated analogue 4. In the former case, a threefold enhancement in the emission intensity could be observed in the gel state, whereas no change in emission occurred in solution. Thus, the major limitations of spontaneous fiber growth and fluorescence self-quenching encountered in the self-assembly of OPVs could be controlled to a great extent by using the versatile ArH-ArF interaction

From vesicles to helical nanotubes: a sergeant-and-soldiers effect in the self-assembly of oligo(p-phenyleneethynylene)s

Coassembly of short molecular wires OPE1 with chiral analogues OPE2, both of which are CD silent, exhibited a sergeant-and-soldiers effect that resulted in transformation of vesicular aggregates of OPE1 into CD-active helical nanotubes (see schematic picture), as revealed by CD, dynamic light scattering, and atomic force and transmission electron microscopies (TEM). OPE=oligo(p-phenyleneethynylene)