Self-Assembled Porous Alumina Based Organic Nanotriode Arrays

We utilize ordered mesoporous alumina templates for solution processable electronics and demonstrate massively parallel organization of connected three-terminal vertical transistors. The vertical transistor device consists of a connected organic nanotriode array obtained using porous anodized alumina membranes of pore density ≈ 10⁹ pores/cm². In this structure, a collector–emitter diode gives rise to a space charge limited current, which can be controlled by a third intermediate porous base electrode to give transistor-like characteristics. We study the response characteristics along with 2D device simulations of this novel structure to indicate key parameters involved in the underlying mechanism. Device operation at single transistor level is verified by conductive atomic force microscopy, and the inherent short switching time scales of the vertical structure device is also demonstrated

Cu Doping in Ligand Free CdS Nanocrystals: Conductivity and Electronic Structure Study

Ligand-free Cu-doped CdS nanocrystals (NCs) have been synthesized to elucidate their surface electronic structure. The Cu-doped ligand-free NCs unlike their undoped counterparts are shown to be luminescent. We used this Cu-related emission as a probe to study the nature of the surface trap states that results in negligible luminescence in the undoped NCs. The concentration of the sulfide ligands is shown to play a crucial role in the surface passivation of the NCs. Electrical conductivity of these NCs was also studied, and they were shown to exhibit significant conductivity of ∼10^–4 S cm^–1. Further we have shown that the electrical conductivity is closely correlated to the surface charge and hence the trap states of the individual NCs have far-reaching consequences in the device optimization

Molecular Architectonics of Naphthalenediimides for Efficient Structure–Property Correlation

We present a bioinspired design strategy to effectively tailor the assembly of naphthalenediimides (NDIs) into a wide variety of architectures by functionalizing with amino acid derivatives. This bioinspired process of custom designing and engineering molecular assemblies is termed “bioinspired architectonics”. By employing minute structural mutations in the form of α-substituents of amino acids, we successfully engineered molecular assembly of NDIs into zero-dimensional (0D, spheres), one-dimensional (1D, fibers), and two-dimensional (2D, sheets) architectures. The 2D sheets of phenylalanine methylester appended NDI <b>1</b> showed remarkable bulk electron mobility of up to 1 cm² V^–1s^–1. With the aid of photophysical, diffraction, and microscopy techniques we rationalize the effect of molecular structure with their ordering and electronic properties in an effort to find structure–property correlations via a bioinspired modular approach

Emergence of Chiroptical Properties in Molecular Assemblies of Phenyleneethynylenes: The Role of Quasi-degenerate Excitations

Chiroptical properties of supramolecular assemblies originate through the asymmetric coupling of molecular transition dipole moments. Herein, we report a joint experimental and theoretical investigation to understand the influence of intermolecular interactions on chiroptical properties, particularly during the early stages of self-assembly. In this regard, phenyleneethynylene-based molecular systems appended with d- and l-isomers of phenylalanine have been synthesized with one as well as two electronic transitions in the spectral region of interest. When self-assembled, these molecules show distinctly different chiroptical properties with the right- and left-handed organizations, guided by the chirality of phenylalanines. The standard exciton approach explains the observation of a bisignated electronic circular dichroism signal in systems with a single transition but fails when applied to systems with two nearby transitions. Here, we present a generalized exciton approach that addresses the unusual chiroptical properties of systems with multiple transitions

Modulation of Electronic and Self-Assembly Properties of a Donor–Acceptor–Donor-Based Molecular Materials via Atomistic Approach

The performance of molecular materials in optoelectronic devices critically depends upon their electronic properties and solid-state structure. In this report, we have synthesized sulfur and selenium based (<b>T4BT</b> and <b>T4BSe</b>) donor–acceptor–donor (D–A–D) organic derivatives in order to understand the structure–property correlation in organic semiconductors by selectively tuning the chalcogen atom. The photophysical properties exhibit a significant alteration upon varying a single atom in the molecular structure. A joint theoretical and experimental investigation suggests that replacing sulfur with selenium significantly reduces the band gap and molar absorption coefficient because of lower electronegativity and ionization potential of selenium. Single-crystal X-ray diffraction analysis showed differences in their solid-state packing and intermolecular interactions. Subsequently, difference in the solid-state packing results variation in self-assembly. Micorstructural changes within these materials are correlated to their electrical resistance variation, investigated by conducting probe atomic force microscopy (<b>CP-AFM</b>) measurements. These results provide useful guidelines to understand the fundamental properties of D–A–D materials prepared by atomistic modulation