Symmetry-Breaking Charge Separation Mediated Triplet Population in a Perylenediimide Trimer at the Single-Molecule Level.

Herein, we demonstrate triplet excited-state population in a conformationally rigid perylenediimide trimer (PDI-T) via intramolecular symmetry-breaking charge separation (SB-CS) at the single-molecule level. The single-molecule fluorescence intensity trajectories of PDI-T in nonpolar polystyrene matrix (ε = 2.60) exhibit prolonged fluorescence with infrequent dark states, representing the triplet and/or the charge transfer states. In contrast, in a poly(vinyl alcohol) matrix (ε = 7.80), erratic blinking dynamics resulting in low photon counts were observed, corroborating the feasibility of charge separation in a polar environment. In agreement with the single-molecule measurements, transient absorption spectroscopy of PDI-T reveals ultrafast SB-CS (τCS < 5 ps) in polar tetrahydrofuran (ε = 7.58) and acetone (ε = 20.70), with the population of the triplet excited-state through charge recombination. The current investigation shows the utility of rigid and weakly coupled molecular constructs in controlling triplet generation and SB-CS for potential applications in optoelectronic devices.

Unveiling the topology of partially disordered micro-crystalline nitro-perylenediimide with X-aggregate stacking: an integrated approach.

Profound knowledge of the molecular structure and supramolecular organization of organic molecules is essential to understand their structure-property relationships. Herein we demonstrate the packing arrangement of partially disordered nitro-perylenediimide (NO2-PDI), revealing that the perylenediimide units exhibit an X-shaped packing pattern. The packing of NO2-PDI is derived using a complementary approach that utilises solid-state NMR (ssNMR) and 3D electron diffraction (3D ED) techniques. Perylenediimide (PDI) molecules are captivating due to their high luminescence efficiency and optoelectronic properties, which are related to supramolecular self-assembly. Increasing the alkyl chain length on the imide substituent poses a more significant challenge in crystallizing the resulting molecule. In addition to the alkyl tails, other functional groups, like the nitro group attached as a bay substituent, can also cause disorder. Such heterogeneity could lead to diffuse scattering, which then complicates the interpretation of diffraction experiment data, where perfect periodicity is expected. As a result, there is an unmet need to develop a methodology for solving the structures of difficult-to-crystallize materials. A synergistic approach is utilised in this manuscript to understand the packing arrangement of the disordered material NO2-PDI by making use of 3D ED, ssNMR and density functional theory calculations (DFT). The combination of these experimental and theoretical approaches provides great promise in enabling the structural investigation of novel materials with customized properties across various applications, which are, due to the internal disorder, very difficult to study by diffraction techniques. By effectively addressing these challenges, our methodology opens up new avenues for material characterization, thereby driving exciting advancements in the field.

Energy landscape of perylenediimide chromophoric aggregates.

Understanding the self-assembly of conjugated organic materials at the molecular level is crucial in their potential applications as active components in electronic and optoelectronic devices. The type of aggregation significantly influences the intriguing electronic and optical characteristics differing from their constituent molecules. Perylenediimides (PDIs), electron-deficient molecules exhibiting remarkable n-type semiconducting properties, are among the most explored organic fluorescent materials due to their high fluorescence efficiency, photostability, and optoelectronic properties. PDI derivatives are reported to form well-tailored supramolecular architectures: cofacial with minor slip (H-aggregates), staggered with major slip (J-aggregates), magic angle stacking (M-aggregates), rotated (X-aggregates), rotated orthogonal ((+)-aggregates), etc. H*-aggregates are defined here as an ideal case of H-aggregate with an eclipsed configuration. Although numerous reports regarding the formation and optical properties of various PDI aggregates are known, the key driving force within the PDI units guiding the self-assembly to form distinct aggregate systems remains elusive. To unravel the molecular-level mechanisms behind the self-assembly of PDI units by probing the intermolecular interactions, symmetry-adapted perturbation theory-based energy decomposition, potential energy surface scans, and non-covalent interaction index analyses were employed on PDI dimer models. Quantum theory of atoms in molecules and frontier molecular orbital analyses were implemented on the dimer models to comprehend the effect of heteroatoms and orbital interactions in stabilising the X-aggregates over the other PDI aggregate systems. Competition between the attractive and repulsive non-covalent interactions dictates a stability order of X > H > J > M > (+) > H* for the PDI aggregate system, while in the parent perylene system, the stability order was found to be X > (+) > H > M > J > H*.

Solvent dielectric delimited nitro-nitrito photorearrangement in a perylenediimide derivative.

The discovery of vibrant excited-state dynamics and distinctive photochemistry has established nitrated polycyclic aromatic hydrocarbons as an exhilarating class of organic compounds. Herein, we report the atypical photorearrangement of nitro-perylenediimide (NO2-PDI) to nitrito-perylenediimide (ONO-PDI), triggered by visible-light excitation and giving rise to linkage isomers in the polar aprotic solvent acetonitrile. ONO-PDI has been isolated and unambiguously characterized using standard spectroscopic, spectrometric, and elemental composition techniques. Although nitritoaromatic compounds are conventionally considered to be crucial intermediates in the photodissociation of nitroaromatics, experimental evidence for this has not been observed heretofore. Ultrafast transient absorption spectroscopy combined with computational investigations revealed the prominence of a conformationally relaxed singlet excited-state (SCR 1) of NO2-PDI in the photoisomerization pathway. Theoretical transition state (TS) analysis indicated the presence of a six-membered cyclic TS, which is pivotal in connecting the SCR 1 state to the photoproduct state. This article addresses prevailing knowledge gaps in the field of organic linkage isomers and provides a comprehensive understanding of the unprecedented photoisomerization mechanism operating in the case of NO2-PDI.