Tunable Charge Transport Using Heterocycles-Flanked Alkoxyphenanthrenes for High-Performing OFETs

A series of new heterocycles-flanked alkoxyphenanthrenes with D'-D-D' and A-D-A architecture was synthesized for high-performance solution-processable p-channel, n-channel, and ambipolar organic field-effect transistors. The impact of electron-donating and -accepting abilities of the sulfur- and nitrogen-containing heteroaromatics on photophysical, electrochemical, and semiconducting properties was analyzed. The presence of heteroaryl rings improves the extended conjugation, two-dimensional lattices of π-π stacks, and increased molecular interaction of the functionalized phenanthrenes (PN) to allow better self-assembly. The electronically dynamic PN self-assembles into continuous microdomains, forming percolation channels for holes, electrons, or both reliant on functionalization. The low-lying LUMO levels of the compounds enabled ambipolar transport and reduced energy levels for charge injections. Spin-coated devices fabricated using functionalized PN with sulfur-containing heteroaryl substituted PN exhibited the highest hole mobility of 0.85 cm2/(V s) with 108 on/off current ratio. Compounds with A-D-A architecture showed n-channel/ambipolar charge transport, especially napthalimide acceptor substituted PN exhibited n-channel electron mobility of 0.78 cm2/(V s) and an on/off ratio of 106. X-ray diffraction and scanning electron microscopy studies further delineate the impact of efficient packing in the film. Quantum chemistry calculations combined with Marcus-Hush electron transfer theory interpret the transport parameters, and heteroatoms are established to impact the charge mobility intensely.

Tweaking the Non-Volatile Write-Once-Read-Many-Times (WORM) Memory using Donor-Acceptor Architecture with Isatin as Core Acceptor

Organic memory devices have attracted attention because they promise flexible electronics, low manufacturing costs, and compatibility with large-scale integration. A series of new D-A architectures were synthesized employing different donor groups and the isatin moiety as the acceptor through Suzuki-Miyaura coupling reactions. Strong intramolecular interactions were observed in the synthesized compounds, further corroborated by an optimal bandgap. The SEM investigation confirmed good molecular ordering and superior thin film surface coverage. All the compounds demonstrated notable binary Write-Once-Read-Many-Times (WORM) memory behaviour. The threshold switching voltage for these D-A systems ranged from -0.79 to -2.37 V, with the compound having isobutyl substituent showing the lowest threshold voltage and maximum ON/OFF ratio of 102, thus outperforming others. The combined effects of charge transfer and charge trapping are responsible for the resistive switching mechanism prevailing in these systems. The alterations in D-A molecules that affect molecular packing, thin film morphology, and, finally, the memory performance of the active layer are highlighted in this work.

A novel class of rigid-rod perylene diimides and isoindigo semiconducting polymers

Three novel rigid-rod semiconducting polymers containing fused electron-deficient PDI and IID units have been synthesized through aldol polymerization. Their unique opto-electronic properties have been investigated systematically.