Modification of carbon nitride based polymeric 2D materials for tailoring their optical, electronic and chemical properties for various applications has gained significant interest. The present report demonstrates the synthesis of a novel modified carbon nitride framework with a remarkable 3:5 C:N stoichiometry (C3N5) and an electronic bandgap of 1.76 eV, by thermal deammoniation of the melem hydrazine precursor. Characterization revealed that in the C3N5 polymer, two s-heptazine units are bridged together with azo linkage, which constitutes an entirely new and different bonding fashion from g-C3N4 where three heptazine units are linked together with tertiary nitrogen. Extended conjugation due to overlap of azo nitrogens and increased electron density on heptazine nucleus due to the aromatic π network of heptazine units lead to an upward shift of the valence band maximum resulting in bandgap reduction down to 1.76 eV. XRD, He-ion imaging, HR-TEM, EELS, PL, fluorescence lifetime imaging, Raman, FTIR, TGA, KPFM, XPS, NMR and EPR clearly show that the properties of C3N5 are distinct from pristine carbon nitride (g-C3N4). When used as an electron transport layer (ETL) in MAPbBr3 based halide perovskite solar cells, C3N5 outperformed g-C3N4, in particular generating an open circuit photovoltage as high as 1.3 V, while C3N5 blended with MA x FA1–x Pb­(I0.85Br0.15)3 perovskite active layer achieved a photoconversion efficiency (PCE) up to 16.7%. C3N5 was also shown to be an effective visible light sensitizer for TiO2 photoanodes in photoelectrochemical water splitting. Because of its electron-rich character, the C3N5 material displayed instantaneous adsorption of methylene blue from aqueous solution reaching complete equilibrium within 10 min, which is significantly faster than pristine g-C3N4 and other carbon based materials. C3N5 coupled with plasmonic silver nanocubes promotes plasmon-exciton coinduced surface catalytic reactions reaching completion at much low laser intensity (1.0 mW) than g-C3N4, which showed sluggish performance even at high laser power (10.0 mW). The relatively narrow bandgap and 2D structure of C3N5 make it an interesting air-stable and temperature-resistant semiconductor for optoelectronic applications while its electron-rich character and intrasheet cavity make it an attractive supramolecular adsorbent for environmental applications.

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Abstract.High spin polarization materials or spin filters are key components in spintronics, a niche subfield of electronics where carrier spins play a functional role. Carrier transmission through these materials is "spin selective" i.e. these materials are able to discriminate between "up" and "down" spins. Common spin filters include transition metal ferromagnets and their alloys, with typical spin selectivity (or, polarization) ~ 50% or less. Here we consider carrier transport in an archetypical one-dimensional molecular hybrid in which a single wall carbon nanotube (SWCNT) is wrapped around by single stranded deoxyribonucleic acid (ssDNA). By magnetoresistance measurements we show that this system can act as a spin filter with maximum spin polarization approaching ~ 74% at low temperatures, significantly larger than transition metals under comparable conditions. Inversion asymmetric helicoidal potential of the charged ssDNA backbone induces a Rashba spin-orbit interaction in the SWCNT channel and polarizes carrier spins. Our results are consistent with recent theoretical work that predicted spin dependent conductance in ssDNA-SWCNT hybrid. Ability to generate highly spin polarized carriers using molecular functionalization can lead to magnet-less and contactless spintronic devices in the future. This can eliminate the conductivity mismatch problem and open new directions for research in organic spintronics. 2 1. Introduction.

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Heterojunctions of the low bandgap semiconductor bismuth oxyiodide (BiOI) with bulk multilayered graphitic carbon nitride (g-C3N4) and few layered graphitic carbon nitride sheets (g-C3N4-S) are synthesized and investigated as an active photoanode material for sunlight driven water splitting.