Modulating the luminance of organic light-emitting diodes via optical stimulation of a photochromic molecular monolayer at transparent oxide electrode

Molecular-Switch-Embedded Solution-Processed Semiconductors

Recent improvements in the performance of solution-processed semiconductor materials and optoelectronic devices have shifted research interest to the diversification/advancement of their functionality. Embedding a molecular switch capable of transition between two or more metastable isomers by light stimuli is one of the most straightforward and widely accepted methods to potentially realize the multifunctionality of optoelectronic devices. A molecular switch embedded in a semiconductor can effectively control various parameters such as trap-level, dielectric constant, electrical resistance, charge mobility, and charge polarity, which can be utilized in photoprogrammable devices including transistors, memory, and diodes. This review classifies the mechanism of each optoelectronic transition driven by molecular switches regardless of the type of semiconductor material or molecular switch or device. In addition, the basic characteristics of molecular switches and the persisting technical/scientific issues corresponding to each mechanism are discussed to help researchers. Finally, interesting yet infrequently reported applications of molecular switches and their mechanisms are also described.

Future-Oriented Advanced Diarylethene Photoswitches: From Molecular Design to Spontaneous Assembly Systems

Diarylethene (DAE) photoswitch is a new and promising family of photochromic molecules and has shown superior performance as a smart trigger in stimulus-responsive materials. During the past few decades, the DAE family has achieved a leap from simple molecules to functional molecules and developed toward validity as a universal switching building block. In recent years, the introduction of DAE into an assembly system has been an attractive strategy that enables the photochromic behavior of the building blocks to be manifested at the level of the entire system, beyond the DAE unit itself. This assembly-based strategy will bring many unexpected results that promote the design and manufacture of a new generation of advanced materials. Here, recent advances in the design and fabrication of diarylethene as a trigger in materials science, chemistry, and biomedicine are reviewed.

Development of metal-free layered semiconductors for 2D organic field-effect transistors

To this day, the active components of integrated circuits consist mostly of (semi-)metals. Concerns for raw material supply and pricing aside, the overreliance on (semi-)metals in electronics limits our abilities (i) to tune the properties and composition of the active components, (ii) to freely process their physical dimensions, and (iii) to expand their deployment to applications that require optical transparency, mechanical flexibility, and permeability. 2D organic semiconductors match these criteria more closely. In this review, we discuss a number of 2D organic materials that can facilitate charge transport across and in-between their π-conjugated layers as well as the challenges that arise from modulation and processing of organic polymer semiconductors in electronic devices such as organic field-effect transistors.

Wafer-Scale and Full-Coverage Two-Dimensional Molecular Monolayers Strained by Solvent Surface Tension Balance

Inspired by the outstanding properties discovered in two-dimensional materials, the bottom-up generation of molecular monolayers is becoming again extremely popular as a route to develop novel functional materials and devices with tailored characteristics and minimal materials consumption. However, achieving a full-coverage over a large-area still represents a grand challenge. Here we report a molecular self-assembly protocol at the water surface in which the monolayers are strained by a novel solvent surface tension balance (SSTB) instead of a physical film balance as in the conventional Langmuir-Blodgett (LB) method. The obtained molecular monolayers can be transferred onto any arbitrary substrate including rigid inorganic oxides and metals, as well as flexible polymeric dielectrics. As a proof-of-concept, their application as ideal modification layers of a dielectric support for high-performance organic field-effect transistors (OFETs) has been demonstrated. The field-effect mobilities of both p- and n-type semiconductors displayed dramatic improvements of 1-3 orders of magnitude on SSTB-derived molecular monolayer, reaching values as high as 6.16 cm² V^-1 s^-1 and 0.68 cm² V^-1 s^-1 for pentacene and PTCDI-C8, respectively. This methodology for the fabrication of wafer-scale and defect-free molecular monolayers holds potential toward the emergence of a new generation of high-performance electronics based on two-dimensional materials.