Naphthalene Diimide-Based Donor-Acceptor-Donor Small Molecules as Metal-Free Organocatalysts for Photocatalytic CO2 Reaction

The application of organic small molecules as metal-free photocatalysts for light-driven photoreduction of carbon dioxide (CO₂) has seldom been explored. This work developed four naphthalene diimide (NDI)-derived donor-acceptor-donor small molecules with different numbers of thiophene units, namely, NDI-2T, NDI-TT, NDI-4T, and NDI-6T, as metal-free photocatalysts to catalyze the reduction of CO₂ under irradiation with an air mass 1.5G solar simulator at one-sun intensity. The structure-property relationship was investigated by exploring the effects of the electron-donating ability of the donor units on the optical properties, redox potential, electron-hole distribution, and exciton lifetime. NDI-6T exhibited the most red-shifted absorption, longest exciton lifetime, and strongest electron-hole separation. However, the large upshift in oxidation potential because of the elevated electron-donating ability of the hexathiophene unit significantly reduced the driving force for catalyst regeneration, leading to poor catalytic performance. Alternatively, NDI-4T possessed proper redox potentials, reduced charge-transfer resistance, and excellent photocurrent intensity; therefore, it effectively converted CO₂ to a single product of CO in the presence of water as an electron donor without a sacrificial reagent or cocatalyst with a product yield of 168.6 μmol g_cat^-1 24 h^-1, which was considerably higher than those of NDI-TT (111.9 μmol g_cat^-1 24 h^-1), NDI-2T (88.4 μmol g_cat^-1 24 h^-1), and NDI-6T (40.5 μmol g_cat^-1 24 h^-1). This study provides a practical guideline for the molecular design of conjugated organic molecules as promising photocatalysts for CO₂ photoreduction.

Synthesis of Cyclopentadithiophene-Diketopyrrolopyrrole Donor-Acceptor Copolymers for High-Performance Nonvolatile Floating-Gate Memory Transistors with Long Retention Time

Organic flash memories that employ solution-processed polymer semiconductors preferentially require internal stability of their active channel layers. In this paper, a series of new donor-acceptor copolymers based on cyclopentadithiophene (CDT) and diketopyrrolopyrrole (DPP) are synthesized to obtain high performance and operational stability of nonvolatile floating-gate memory transistors with various additional donor units including thiophene, thiophene-vinylene-thiophene (CDT-DPP-TVT), selenophene, and selenophene-vinylene-selenophene. Detailed analyses on the photophysical, two-dimensional grazing incident X-ray diffraction, and bias stress stability are discussed, which reveal that the CDT-DPP-TVT exhibits excellent bias stress stability over 10⁵ s. To utilize the robust nature of CDT-DPP-TVT, floating-gate transistors are fabricated by embedding Au nanoparticles between Cytop layers as a charge storage site. The resulting memory devices reveal bistable current states with high on/off current ratio larger than 10⁴ and each state can be distinguished for more than 1 year, indicating a long retention time. Moreover, repetitive writing-reading-erasing-reading test clearly supports the reproducible memory operation with reversible and reliable electrical responses. All these results suggest that the internal stability of CDT-DPP-TVT makes this copolymer a promising material for application in reliable organic flash memory.

Naphthalene flanked diketopyrrolopyrrole: a new conjugated building block with hexyl or octyl alkyl side chains for electropolymerization studies and its biosensor applications

Naphthalene flanked DPP with hexyl and octyl chain based electropolymerized conjugated polymers exhibits bio-sensing.

Towards more sustainable synthesis of diketopyrrolopyrroles

Functionalisation of diketopyrrolopyrroles with improved energy use during synthesis, ease of isolation, and yields of reactions is reported.

A comparative analysis of symmetric diketopyrrolopyrrole-cored small conjugated molecules with aromatic flanks: From geometry to charge transport

Diketopyrrolopyrrole (DPP) derivatives are promising compounds for application in organic electronics. Here, we investigate several symmetrical N-unsubstituted and N-methyl substituted DPPs which differ in the heteroatom in the aromatic flanks. The conformational, electronic, and optical properties are characterized for single molecules in vacuum or a solvent. The intermolecular interactions are evaluated for interacting dimers. Here, a number of stacking geometries is tested, and dimers with mutual orientation of the molecules corresponding to the minimal binding energies are determined. The predicted charge carrier mobilities for stacks having minimal binding energies corroborate experimentally measured values. We conclude that DFT prediction of such stacks is a promising and computationally inexpensive approach to a rough estimation of transport properties. Additionally, the super-cell of the experimentally resolved crystal structure is used to study the dynamics and to compute the charge transport along the hopping pathways. We discuss obtained high mobilities and relate them to the symmetry of DPP core. © 2018 Wiley Periodicals, Inc.