Stimuli‐responsive materials have raised major attention in digital technology, sensors and biomedical applications owing to quick response towards external stimuli, for example light, voltage, pressure, temperature, mechanical friction and pH. Nevertheless, action of external stimuli on organic materials affects their internal physico‐chemical properties and facilitates improved thermal/photo stability, tuning detection sensitivity, accuracy and biocompatibility. This review article highlights recent progress on stimuli‐responsive materials with mixed valence species, viologens, twisting chirality, crystalline/amorphous, sol‐gel phase transitions and resulting supramolecular nanostructures via non‐covalent interactions. These materials can be applied in flexible electronics, drug delivery, detection of pollutants and bioimaging. Thus, the demand for widespread research on development of stimuli‐responsive materials are requisite to resolve the challenges pertaining to stability and sensitivity of devices for design in comprehensive technology.

Hole transporting material (HTM) is a significant component to achieve the high performance perovskite solar cells (PSCs). Over the years, inorganic, organic and hybrid (organic-inorganic) material based HTMs have been developed and investigated successfully. Today, perovskite solar cells achieved the efficiency of 22.1 % with with 2,2',7,7'-tetrakis(N,Ndi-p-methoxyphenyl-amine) 9,9-spirobifluorene (spiro-OMeTAD) as HTM. Nevertheless, synthesis and cost of organic HTMs is a major challenging issue and therefore alternative materials are required. From the past few years, inorganic HTMs showed large improvement in power conversion efficiency (PCE) and stability. Recently CuO x reached the PCE of 19.0% with better stability. These developments affirms that inorganic HTMs are better alternativesto the organic HTMs for next generation PSCs. In this report, we mainly focussed on the recent advances of inorganic and hybrid HTMs for PSCs and highlighted the efficiency and stability of PSCs improved by changing metal oxides as HTMs. Consequently, we expect that energy levels of these inorganic HTMs matches very well with the valence band of perovskites and improved efficiency helps in future practical deployment of low cost PSCs.

Co-sensitization is a popular route towards improved efficiency and stability of dye-sensitized solar cells (DSSCs). In this context, the power conversion efficiency (PCE) values of DSSCs incorporating Ru- and porphyrin-based dyes can be improved from 8-11 % to 11-14 % after the addition of additives, co-adsorbents, and co-sensitizers that reduce aggregation and charge recombination in the device. Among the three supporting material types, co-sensitizers play a major role to enhance the performance and stability of DSSCs, which is requried for commercialization. In this Minireview, we highlight the role co-sensitizers play in improving photovoltaic performance of devices containing Ru- and porphyrin-based sensitizers.

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Self-assembled π-conjugated molecules exhibit switching between crystalline−amorphous nanostructures, attracting significant interest in the field of organic electronics, particularly memory devices. Herein, we report ferroceneappended tetratolylporphyrin, H 2 TTP-Fc, which undergoes protonation in 1,2-dichloroethane via sonication and reverses to the original state by deprotonation with time, as confirmed by optical and electrochemical properties. Absorption spectra reveal the selectivity of reversible and irreversible protonation of H 2 TTP-Fc in halogenated solvents and mineral acids. Microscopic analysis suggested that H 2 TTP-Fc aggregates exhibit a crystalline flower-like morphology from the joining of 2D microsheets, whereas H 4 TTP-Fc forms nanospheres with an average diameter of 150−200 nm upon methanol vapor diffusion (MVD). Electrochemical properties of H 4 TTP-Fc films reveal the ease of oxidation when compared to that in the solution state as a result of high current generation at less work function. Therefore, these novel features aid the design of efficient organic redox-active materials for hazardous pollutant detection and organic−electronic applications.

Today's solar cells are exceptionally in demand whilst excess exploitation of natural fossil fuels. In this context, the first and second generation solar cells commercially available in market for more than decades however limitations in production cost and large-scale applications insist to generate inexpensive materials for fabrication. Thereby, organic materials based solar cells explored and emerging as third generation solar cells which possess flexibility, low cost and large-scale applications. For example, organic photovoltaics, dye sensitized solar cells and perovskite (organic-inorganic) solar cells (PSCs) are considered third generation solar cells wherein PSCs reached the record power conversion efficiency (PCE~23 %) and durability assists great advantages for commercialization in near future. Moreover, we reported various global renowned companies involved producing the modules and materials for three generation solar cells, hence, majority of companies considered commercialization of perovskite based solar cells assist low cost photovoltaics to meet the current energy necessities and environmental safety.

Tetrapyrrolic systems largely inspired by nature have attracted much attention in organic electronics and biomedical applications owing to their planar structure and extended [Formula: see text]-conjugated double bonds. As a result, delocalization of [Formula: see text]-electron cloud leads the excellent optical absorption and fluorescent properties. Nonetheless, the utilization of non-covalent interactions result in the self-assembled nanostructures providing applications in bioimaging and electronics. In this review, it is demonstrated that the recent reports on the self-assembly in tetrapyrrolic systems via supramolecular interactions lead to well-defined nanoarchitectures. Moreover, the importance of porphyrin based derivatives in nanoelectronics and chemotherapeutic applications is reported. Therefore, the inclination of tetrapyrroles towards the design and development of novel supramolecular nanostructures are considered the hallmark for nanorobotics, shape memory polymers and bionic arms.

Scrolling mechanism is considered as a significant process to tune the dimensionality of nanostructures. Remarkably, rolling of ultrathin two-dimensional (2D) layered graphene nanosheets into one-dimensional (1D) nanotubes perceived versatile applications in nanomedicine and organic electronics. Nevertheless, this exceptional phenomenon is observed in limited 2D π-conjugated systems until now, and it is essential to extend it toward feasible organic systems. Herein, we reported two porphyrin-derived systems (P1 and P2), in which P2 composed of porphyrin and benzothiadiazole with directional amide hydrogen-bonding moiety acts as a good electron donor–acceptor system. Consequently, P2 showed high-conducting 1D nanofibers from the diagonal scrolling of 2D nanosheets via in situ self-assembly. Photophysical properties of P2 revealed J-type aggregates in cyclohexane, while P1 exists as monomers. Cyclic voltammetry analysis of P2 showed the ease of oxidation compared to P1 owing to the efficient electron transfer from donor to acceptor derivative. Microscopic analysis suggests that P2 depicts 2D nanosheets with an average diameter of 1–3 μm upon diagonal scrolling of 1D nanofibers of width 1–1.5 μm and length several micrometers. Electrochemical impedance analysis revealed that 1D nanofibers of P2 depict electrical conductivity in the range of 1.5 ± 0.2 S/cm. Thereby, these derivatives highlight that NIR absorption and their efficient optoelectronic characteristics promote the alternatives for inorganic semiconductors in organic electronics.