M. Pandeeswar

Chiral Transcription and Retentive Helical Memory: Probing Peptide Auxiliaries Appended with Naphthalenediimides for Their One-Dimensional Molecular Organization

Right or left paradox: Homochiral, heterochiral and achiral peptide auxiliaries appended with naphthalenediimide (NDI, see figure) were employed to demonstrate chiral transcription. We report an interesting phenomenon coined as retentive helical memory. Remarkably, NDI-peptide conjugates were tuned into hierarchical 1D molecular assemblies of opposite helicity in case of homochiral peptide auxiliaries.

Assembly Modulation of PDI Derivative as a Supramolecular Fluorescence Switching Probe for Detection of Cationic Surfactant and Metal Ions in Aqueous Media

We report an amphiphilic perylene diimide (1), a bimolecular analog of l-3,4-dihydroxyphenylalanine (L-DOPA), as a reversible fluorescence switching probe for the detection and sensing of cationic surfactants and Fe(3+)/Cu(2+) in an aqueous media respectively by means of host-guest interactions driven assembly and disassembly of 1. Photophysical studies of 1, going from dimethyl sulfoxide (DMSO) (State-I) to pure aqueous medium (State-II), suggested the formation of self-assembled aggregates by displaying very weak fluorescence emission along with red shifted broad absorption bands. Interestingly, the cationic surfactant cetyltrimethylammonium bromide (CTAB) could disassemble 1 in miceller conditions by restoring bright yellow fluorescence and vibronically well-defined (Franck-Condon progressions A0-0/A0-1 ≈ 1.6) absorption bands of 1 over other neutral and anionic surfactants (State-III). Owing to the metal chelating nature of L-DOPA, 1 was able to sense Fe(3+) and Cu(2+) among a pool of other metal ions by means of fluorescence switching off state, attributed to metal interaction driven assembly of 1 (State-IV). Such metallosupramolecular assemblies were found to reverse back to the fluorescence switching on state using a metal ion chelator, diethylenetriaminepentaacetic acid (DTPA, State-III), further signifying the role of metal ions toward assembly of 1. Formation of assembly and disassembly could be visualized by the diminished and increased yellow emission under green laser light. Further, the assembly-disassembly modulation of 1 has been extensively characterized using infrared (IR), mass spectrometry, microscopy and dynamic light scattering (DLS) techniques. Therefore, modulation of the molecular self-assembly of PDI derivative 1 in aqueous media (assembled state, State-II) by means of host-guest interactions provided by micellar structures of CTAB (disassembled state, State-III), metal ion (Fe(3+) and Cu(2+)) interactions (assembled state, State-IV) and metal ion sequestration using DTPA (disassembled state, State-III) is viewed as a supramolecular reversible fluorescence switching off-on probe for cationic surfactant CTAB and Fe(3+)/Cu(2+).

Spontaneous self-assembly of designed cyclic dipeptide (Phg-Phg) into two-dimensional nano- and mesosheets

In this study, we present the spontaneous self-assembly of designed simplest aromatic cyclic dipeptides of (l-Phg-l-Phg) and (d-Phg-l-Phg) to form highly stable two-dimensional (2D) nano- and mesosheets with large lateral surface area. Various microscopy data revealed that the morphology of 2D mesosheets resembles the hierarchical natural materials with layered structure. Solution and solid-state NMR studies on cyclo(l-Phg-l-Phg) revealed the presence of strong (N–H–O) hydrogen-bonded molecular chains supported by aromatic π–π interactions to form 2D mesosheets. Interestingly, cyclo(d-Phg-l-Phg) self-assembles to form single-crystalline as well as non-crystalline 2D rhomboid sheets with large lateral dimension. X-ray diffraction analysis revealed the stacking of (N–H–O) hydrogen-bonded molecular layers along c-axis supported by aromatic π–π interactions. The thermogravimetric analysis shows two transitions with overall high thermal stability attributed to layered hierarchy found in 2D mesosheets.

Bioinspired Nanoarchitectonics of Naphthalene Diimide to Access 2D Sheets of Tunable Size, Shape, and Optoelectronic Properties

A bioinspired nanoarchitectonics design strategy is adapted to construct 2D sheets of promising n-type organic semiconductor naphthalene diimide (NDI) with tunable size, shape and optoelectronic properties. Modulation of noncovalent interactions such as intermolecular NDI–NDI aromatic and hydrogen bonding interactions among the molecules within the self-assembled 2D sheets is achieved by the minute structural mutations on the NDI imide substitutions in the form of glycine derivatives (carboxylic acid, amide and ester). Microscopy studies (FESEM and AFM) showed the formation of flat, smooth and large 2D nanosheets with distinct lateral and height profiles. Photophysical studies revealed unique solid state optoelectronic properties with promising temperature responsive fluorescence behavior with quite longer life time values which are useful as temperature sensor materials. The concentration and temperature dependent 1H NMR and IR studies provided the insights into distinct noncovalent interactions responsible for the observed NDI 2D sheets with variable size and shape. Furthermore, PXRD studies revealed highly crystalline molecular organization within the 2D sheets. On account of these tunable unique properties, the 2D sheets derived from NDI-conjugates might find a wide range of future interdisciplinary applications from materials to biomedicine.

Biomimetic molecular organization of naphthalene diimide in the solid state: tunable (chiro-) optical, viscoelastic and nanoscale properties

The interfacing of aromatic molecules with biomolecules to design functional molecular materials is a promising area of research. Intermolecular interactions determine the performance of these materials and therefore, precise control over the molecular organization is necessary to improve functional properties. Herein we describe the tunable biomimetic molecular engineering of a promising n-type organic semiconductor, naphthalene diimide (NDI), in the solid state by introducing minute structural mutations in the form of amino acids with variable Cα-functionality. For the first time we could achieve all four possible crystal packing modes, namely cofacial, brickwork, herringbone and slipped stacks of the NDI system. Furthermore, amino acid conjugated NDIs exhibit ultrasonication induced organogels with tunable visco-elastic and temperature responsive emission properties. The amino acid–NDI conjugates self-assemble into 0D nanospheres and 1D nanofibers in their gel state while the ethylamine–NDI conjugate forms 2D sheets from its solution. Photophysical studies indicated the remarkable influence of molecular ordering on the absorption and fluorescence properties of NDIs. Interestingly, the circular dichroism (CD) and X-ray diffraction (XRD) studies revealed the existence of helical ordering of NDIs in both solution and solid state. The chiral amino acids and their conformations with respect to the central NDI core are found to influence the nature of the helical organization of NDIs. Consequently, the origin of the preferential handedness in the helical organization is attributed to transcription of chiral information from the amino acid to the NDI core. On account of these unique properties, the materials derived from NDI-conjugates might find a wide range of future interdisciplinary applications from materials to biomedicine.

Green-fluorescent naphthalene diimide: conducting layered hierarchical 2D nanosheets and reversible probe for detection of aromatic solvents

We report the molecular engineering of asymmetrically functionalized naphthalene diimide (NDI) with a simple amino acid into robust self-assembled free-standing, green-fluorescent and conducting layered hierarchical 2D nanosheets which exhibit chiral and crystalline molecular packing. Remarkably the NDI–amino acid conjugate displays tunable fluorescence emission (wavelength range 400–540 nm) properties in aromatic solvents. Furthermore we have exploited the phenomenon of excimer to exciplex transformation to develop a filter paper-based reversible fluorometric test kit for the detection of benzene, a well-known classified carcinogen.

Engineering molecular self-assembly of perylene diimide through pH-responsive chiroptical switching

The perturbation of non-covalent interactions induced by pH-responsive protonation–deprotonation in HPH resulted in reversible supramolecular chiroptical switching (left-handed to right-handed helical self-assembly) and tunable 1D nanostructures.

Covalent crosslinking of carbon nanostructures

AbstractCovalent crosslinking of carbon nanostructures of different dimensionalities such as nanodiamond, single walled carbon nanotubes (SWNTs) and graphene can yield useful homo- and hetero-binary conjugates. Binary conjugation of the nanocarbons has been achieved by introducing symmetrical amide-linkages between acid (-COOH) functionalized nanocarbons and a diamine-linker. The binary conjugates have been characterized by using transmission electron microscopy as well as infrared, Raman and photoluminescence spectroscopies. Dispersions of covalently crosslinked binary conjugates of nanocarbons could be obtained in dimethyl formamide (DMF). Composites of the binary conjugates with polymer can be readily prepared by using the DMF suspensions. Graphical AbstractCovalent crosslinking of carbon nanostructures of different dimensionalities such as nanodiamond, single-walled carbon nanotubes (SWNTs) and graphene yield useful homo- and hetero-binary conjugates. Dispersions of covalently crosslinked binary conjugates of nanocarbons could be obtained in dimethyl formamide (DMF).