Viologens, functional organic materials composed of conjugated bi-/multi-pyridyl groups, have attracted much attention for decades owing to their properties such as unique electrochromic and radical-rich features under redox manipulation, biosensitive properties, and ionic and localized conjugation. Considerable efforts have been devoted to synthesizing novel viologen-based functional materials to study their properties and develop applications. So far, viologens and viologen-based materials have been widely applied in many fields, including electrochromism, molecular machines, memory devices, gas storage and separation, energy storage, and biochemistry. The rapid development of functional materials in the 21^st century has inspired extensive integration of viologens into many types of novel and famous materials (e.g., host–guest supramolecules, porous polymers, and metal–organic frameworks), and therefore, viologens seem to no longer be a key player. However, the features of viologens (or bi-/multi-pyridyl-based materials) have always dominated the properties of target functional materials and long been neglected by researchers. In order to provide an overview of this field, this perspective paper focuses on reasonable design and synthesis of viologen-based functional materials and their representative applications. The remaining challenges and future potential applications are also discussed.

Phthalocyanines (Pcs) offer a high architectural flexibility in structure, which facilitates the tailoring of their physical, optoelectronic and chemical parameters over a very broad range. This tutorial review describes the recent advances in the synthesis of soluble axially substituted or bridged gallium phthalo- and naphthalocyanine compounds, and their photophysical and nonlinear optical properties. The exploitation of the chemical reactivity of the Ga–Cl bond can allow the preparation of a series of highly soluble axially substituted and bridged Pc complexes. Axial substituents in Pcs influence favourably nonlinear optical absorption for the presence of a dipole moment perpendicular to the macrocycle in the axially substituted phthalocyanines. All Z-scans performed exhibit a decrease of transmittance about the focus typical of an induced positive nonlinear absorption of incident light. Substitution and dimerization of the phthalocyanine monomer resulted in significant reductions in the saturation energy density of the material displaying clear evidence of the usefulness of structurally modifying the gallium phthalocyanine unit. Similar to indium phthalocyanines, gallium phthalocyanines are also among the most promising materials that have been investigated as limiters of intense light and the current series presents a selection of structural modifications useful for varying their nonlinear optical properties.

Polymer materials have been considered as promising candidates for the implementation of memristor devices due to their low-cost, easy solution processability, mechanical flexibility and ductibility, tunable electronic performance through innovative molecular design cum synthesis strategy and compatibility with complementary metal oxide semiconductor (CMOS) technology as well. The digital-type polymer memristor behaves as resistive random access memory with non-volatility, high density, more speed, low power consumption, large ON/OFF ratio, high endurance and long retention, and is recognized as an appealing candidate for the next generation “universal memory”. As a logic component, the analog-type memristor, with the ability to emulate the fundamental synaptic functions of short-term/long-term plasticity (STP/LTP), spike-timing dependent-plasticity (STDP), spike-rate dependent plasticity (SRDP) and “learning-experience” behaviors, can be used to construct artificial neural networks for neuromorphic computation. In this review, we shall attempt to summarize the recent progress in research on the materials, switching characteristics and mechanism aspects of two terminal polymer memristors, for both information storage and neuromorphic applications that inspire great interest in the industrial and academic communities.

As the thinnest material ever known in the universe, graphene has been attracting tremendous amount of attention in both materials science and condensed-matter physics since its successful isolation a few years ago. This one-atom-thick two-dimensional pseudo-infinite nano-crystal consists of sp²-hybridized aromatic carbon atoms covalently packed into a continuous hexagonal lattice. Graphene exhibits a range of unique properties, viz., high three-dimensional aspect ratio and large specific surface area, superior mechanical stiffness and flexibility, remarkable optical transmittance, extraordinary thermal response and excellent electronic transport properties, promising its applications in the next generation electronics. To switch graphene and its derivatives between ON and OFF states in nanoelectronic memory devices, various techniques have been developed to manipulate the carbon atomic sheets via introducing the valence–conduction bandgap and to enhance their processability. In this article, we review the utilization of electrically, thermally and chemically modified graphene and its polymer-functionalized derivatives for switching and information storage applications. The challenges posed on the development of novel graphene materials and further enhancements of the device switching performance have also been discussed.