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Compaction of nucleic acids, namely DNA and RNA, determines their functions and involvement in vital cell processes including transcription, replication, DNA repair and translation. However, experimental probing of the compaction of nucleic acids is not straightforward. In this study, we suggest an approach for this probing using low-frequency Raman spectroscopy. Specifically, we show theoretically, computationally and experimentally the quantifiable correlation between the low-frequency Raman intensity from nucleic acids, magnitude of thermal fluctuations of atomic positions, and the compaction state of biomolecules. Noteworthily, we highlight that the LF Raman intensity differs by an order of magnitude for different samples of DNA, and even for the same sample in the course of long-term storage. The feasibility of the approach is further shown by assessment of the DNA compaction in the nuclei of plant cells. We anticipate that the suggested approach will enlighten compaction of nucleic acids and their dynamics during the key processes of the cell life cycle and under various factors, facilitating advancement of molecular biology and medicine.

Derivatives of naphthalene-diimide (NDI) are among the most studied and popular organic semiconductors showing n-type conductivity. However, the structure and optoelectronic properties of crystalline NDIs N -functionalized with conjugated donors have not been investigated yet. In this study, a novel donor-acceptor compound NDI-Stb bearing one NDI core, as an acceptor, and two stilbene moieties covalently linked via imide positions of NDI, as a donor, was synthesized. A combined experimental and theoretical approach was applied to study the structure and properties of NDI-Stb molecules and its crystals. We found and explained why optical absorption and high-frequency Raman spectra are inherited from those of donor and acceptor moieties, but photoluminescence is determined by the properties of the whole molecule. We resolved the structure of NDI-Stb single crystals and found that strong intermolecular interactions operate along two directions, for which NDI cores stack either on similar cores or on stilbene moieties. These interactions cause suppression of dynamic disorder indicated by a weak low-frequency Raman signal and solid-state luminescence enhancement. Ambipolar charge transport was predicted, and electron transport was experimentally observed in NDI-Stb polycrystalline thin films. The results obtained highlight the potential of using NDIs N -functionalized with conjugated donor moieties in optoelectronic applications, and improve the understanding of structure-property relationships necessary for the rational design of novel donor-acceptor organic semiconductors.

Properties of the organic semiconductors can be finely tuned via changes in their molecular structure. However, the relationship between the molecular structure, molecular packing, and (opto)electronic properties of the organic semiconductors to guide their smart design remains elusive. In this study, we address computationally and experimentally the impact of subtle modification of a thiophene-phenylene co-oligomer CF 3 -PTTP-CF 3 on the molecular properties, crystal structure, charge transport, and optoelectronic properties. This modification consists in the substitution of two C-H atom pairs by N atoms in the thiophene units and hence converting them to thiazole units. A dramatic effect of the N-substitution on the crystal structure-the crossover from the herringbone packing motif to π-stacking-is attributed to significant changes in the molecular electrostatic potential. The changes in the molecular and crystal structure resulting from the N-substitution clearly reveal themselves in the Raman spectra. The increase of the calculated electron mobility in the corresponding crystals as a result of the N-substitution is rationalized in terms of the changes in the molecular and crystal structure. The charge transport, electroluminescence, and photoelectric properties are compared in thin-film organic field-effect transistors based on CF 3 -PTTP-CF 3 and its N-substituted counterpart. An intriguing similarity between the effects of N-substitution in the thiophene rings and fluorination of the thiophene-phenylene oligomer is revealed, which is probably associated with a more general effect of electronegative substitution. The obtained results are anticipated to facilitate the rational design of organic semiconductors., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)