Abstract
Polymeric carbon nitride materials have been used in numerous light‐to‐energy conversion applications ranging from photocatalysis to optoelectronics. For a new application and modelling, we first refined the crystal structure of potassium poly(heptazine imide) (K‐PHI)—a benchmark carbon nitride material in photocatalysis—by means of X‐ray powder diffraction and transmission electron microscopy. Using the crystal structure of K‐PHI, periodic DFT calculations were performed to calculate the density‐of‐states (DOS) and localize intra band states (IBS). IBS were found to be responsible for the enhanced K‐PHI absorption in the near IR region, to serve as electron traps, and to be useful in energy transfer reactions. Once excited with visible light, carbon nitrides, in addition to the direct recombination, can also undergo singlet–triplet intersystem crossing. We utilized the K‐PHI centered triplet excited states to trigger a cascade of energy transfer reactions and, in turn, to sensitize, for example, singlet oxygen (1O2) as a starting point to synthesis up to 25 different N‐rich heterocycles.
Highlights
Artificial photosynthesis has been the primary area of inorganic semiconductors application in chemistry for many years.[1,2,3] carbon nitrides are traditionally associated with water splitting and CO2 conversion.[4,5,6] the evolution of hydrogen from water in the case of polymeric carbon nitride impacted work in related areas, such as photoelectrochemical cells,[7] metal-free electrodes,[8,9] and electroluminescence devices.[10]
K-PHI was prepared from 5-aminotetrazole in LiCl/KCl eutectics using mechanochemical pre-treatment of the respective precursors,[40] while details regarding its characterization are given in Figure S1 in the Supporting Information
Fast Fourier Transforms (FFTs) obtained from the high-resolution transmission electron microscopy (HRTEM) images can be indexed in a hexagonal lattice with unit cell parameters a = 11.4(8) and c = 3.7(2)
Summary
Artificial photosynthesis has been the primary area of inorganic semiconductors application in chemistry for many years.[1,2,3] carbon nitrides are traditionally associated with water splitting and CO2 conversion.[4,5,6] the evolution of hydrogen from water in the case of polymeric carbon nitride impacted work in related areas, such as photoelectrochemical cells,[7] metal-free electrodes,[8,9] and electroluminescence devices.[10]. Pconjugated triplet sensitizers have been a topic of research in past decades and have been quite successfully used in areas such as light energy conversion, LEDs fabrication,[31,32] photon upconversion,[33,34,35] cells imaging.[36] only few examples are known using such materials in photocatalysis.[37] Notable is that their use has been restricted to “model” reactions.[38] Most of these solid-state sensitizers are made out of soft polymer matrices with encapsulated platinum group metal complexes.[39]. By virtue of 1O2 mediated reactions, which are surprisingly restricted to the synthesis of model compounds only, many questions and challenges evolve around the function of carbon nitrides. Interaction of 1O2 with aldoximes gives nitrile oxides, which triggered our interest in exploring the synthesis of various oxadiazoles and isoxazoles via dipolar [3+2]-cycloaddition
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