Modulation of Electronic Mobility of a One-Dimensional Coordination Polymeric Molecular Wire with Light

Coordination polymers: a promising candidate for photo-responsive electronic device application

The design and synthesis of electrically conductive coordination polymers (CPs) are of special interest due to their applications in the fabrication of many environmentally benign emerging technologies, such as molecular wires, photovoltaic cells, light emitting diodes (LEDs), field effect transistors (FETs) and Schottky barrier diodes (SBDs). Owing to their structural flexibility, easy functionality and adjustable energy levels, CPs are promising candidates for providing a better pathway for superior charge transport. Again, the utilization of visible light as an external stimulus to control and manoeuvre the electrical properties of the CPs is exceptionally motivating for the development of many optoelectronic devices, such as photodetectors, photo-switches, photodiodes and chemiresistive sensors. The applications of such materials in devices will solve questions regarding the energy crisis and environmental concerns. This study provides an overview of the recent advances in the development of photo-responsive CPs and the possibility of their application in developing optoelectronic devices. In this regard, a thorough literature survey was performed and the studies related to the fabrication of photosensitive conducting CPs for applications in optoelectronic devices are listed.

Light-driven modulation of electrical conductance with photochromic switches: bridging photochemistry with optoelectronics

Photochromic conducting molecules have emerged because of their unique capacity to modulate electrical conductivity upon exposure to light, toggling between high and low conductive states. This unique amalgamation has unlocked novel avenues for the application of these materials across diverse areas in optoelectronics and smart materials. The fundamental mechanism underpinning this phenomenon is based on the light-driven isomerization of conjugated π-systems which influences the extent of conjugation. The photoisomerization process discussed here involves photochromic switches such as azobenzenes, diarylethenes, spiropyrans, dimethyldihydropyrenes, and norbornadiene. The change in the degree of conjugation alters the charge transport in both single molecules and bulk states in solid samples or solutions. This article discusses a number of recent examples of photochromic conducting systems and the challenges and potentials of the field.

Triplet sensitization enables bidirectional isomerization of diazocine with 130 nm redshift in excitation wavelengths

Diazocines are bridged azobenzenes with phenyl rings connected by a CH2-CH2 group. Despite this rather small structural difference, diazocine exhibits improved properties over azobenzene as a photoswitch and most importantly, its Z configuration is more stable than the E isomer. Herein, we reveal yet another unique feature of this emerging class of photoswitches. In striking contrast to azobenzenes and other photochromes, diazocine can be selectively switched in E → Z direction and most intriguingly from its thermodynamically stable Z to metastable E isomer upon successive excitation of two different triplet sensitizers present in solution at the same time. This approach leads to extraordinary large redshift of excitation wavelengths to perform isomerization i.e. from 400 nm blue to 530 nm green light (Z → E) and from 530 nm green to 740 nm far-red one (E → Z), which falls in the near-infrared window in biological tissue. Therefore, this work opens up of potential avenues for utilizing diazocines for example in photopharmacology, smart materials, light energy harvesting/storage devices, and out-of-equilibrium systems.

Triazonine-based bistable photoswitches: synthesis, characterization and photochromic properties

We disclose here dibenzotriazonines as a new class of nine-membered cyclic azobenzenes displaying a nitrogen function in the saturated ring chain. The specific features of these compounds are (i) a preferred E-configuration, (ii) high bi-directional photoswitching and (iii) good thermal stability of both E- and Z-forms.

Metal Ion Mediated Instant Z → E Isomerization of Azobenzene Macrocycles in the Absence of Light

The classical photoswitch azobenzenes reversibly interconvert between the E- and the Z-isomers with light. Here, we report a pair of new macrocyclic azobenzenes characterized thoroughly by spectroscopic methods and single crystal X-ray diffraction structures, and one of the compounds displays a quantitative conversion of the E- to the Z-form. These compounds, besides their normal photoswitching behavior, display an unusual instant switching of the Z-form to the E-isomer in the presence of Cu²⁺ ions in the dark under 273 K. The Cu²⁺ complex can stay in the Z-form under constant UV radiation. However, it reverts to the E-form as soon as the exposure to the UV is ceased. The same phenomenon is also observed with Ag⁺ ions albeit it is a bit slower. This unusual instant switching of the azobenzene systems with metal ions prompted the detailed studies to unravel the reason behind this behavior.

Three Mn–viologen complexes containing 1-carboxyethyl-4,4′-bipyridinium: crystal structures, photochromism and theoretical calculations

Three Mn–viologen complexes containing CEbpy were prepared and displayed excellent photochromic properties by intramolecular or intermolecular electron transfer.