In the present work, eight molecules with different molecular architectures were modelled using computational chemistry, varying the positions of benzothiadiazole (BT) and diketopyrrolopyrrole (DPP) as the acceptor segments, in relation to fluorene (F) as the donor segment. DFT was employed to calculate their overall reactivity parameters, revealing that structures with the highest degree of conjugation and D-A-D architecture were the most stable. DPP influences electronic delocalisation in the presence of BT, acting as the most acceptor-like segment. All eight molecules potentially exhibit a non-linear response, which could be utilised in two-photon absorption applications to enhance radiation penetration, using red and near-infrared wavelengths to activate the molecules. Theoretical absorption spectra indicate no significant red-shift with increasing conjugation length, with absorption occurring within the phototherapeutic range. The emission spectra display relatively high Stokes shifts, indicating that a significant amount of energy relaxes through vibrational pathways such as intersystem crossing, which favours potential ROS production. Finally, the analysis of the excited state energy levels reveals that the molecular structure does not affect the potential for reactive oxygen species generation via mechanisms I and II. Notably, molecule 8, with a D-π-A1-π-π-A2-π-D structure, emerges as the most promising candidate for a potential photosensitiser.

Precision measurements of molecular hydrogen and its isotopologues provide critical tests of molecular theory, including quantum electrodynamics (QED) and fundamental constants. However, advancing the experimental accuracy of hydrogen overtone transitions remains challenging due to unexplained asymmetries in spectral line profiles. We present the Lamb dip measurement at a temperature as low as 12 K, where the spectral features exhibit enhanced resolution. By applying a lineshape centroid extrapolation method – which is independent of the lineshape model – we determine the transition frequency of the R(0) line in the (2-0) overtone of HD to be 214 905 335 170 ( 27 ) stat ( 124 ) sys kHz. While the low-temperature Lamb-dip measurements challenge conventional models of spectral line shapes, our results are in excellent agreement with the latest theoretical results.

A major challenge in using spin-flip time-dependent density functional theory (SF-TD-DFT) for spin-flip-down excitations is the presence of spin contamination. While several improved methods have been developed in the past, a simple and accurate method remains elusive. Here, based on our previous development on spin-adapted open-shell TD-DFT for spin-conserving excitations (X-TD-DFT) [Li and Liu, J. Chem. Phys. 135, 194106 (2011)], we introduce a spin-adapted method within the Tamm-Dancoff approximation (TDA) termed as XSF-TDA for describing spin-flip-down excitations from a high-spin reference state with any spin S i ≥ 1 , and provide an in-depth comparison of different methodologies for mitigating spin contamination in SF-TDA. Pilot applications to prototype systems demonstrate the promise of XSF-TDA over existing SF-TDA methods, including unrestricted SF-TDA (USF-TDA) and mixed-reference SF-TDA (MRSF-TDA), in describing bond breakings and inverted singlet-triplet gap systems.

At present, InN-based semiconductors still have limited effectiveness in extending the infrared spectral response range for applications such as infrared thermophotovoltaic cells, infrared photodetectors, or infrared semiconductor lasers. This limitation hinders the utilisation of solar energy. In exploring more effective ways of broadening the infrared spectral response, the generalised gradient approximation (GGA + U) with plane-wave ultrasoft pseudopotentials based on spin-density functional theory was used to investigate the effects of Li doping and point defects on the electronic structure and optical properties of InN using first-principle calculations. The formation energy calculations reveal that all doped systems are more stable under N-rich conditions than under In-rich conditions. Under N-rich conditions, the formation energies are all negative, indicating that the doped systems are easily formed and remain stable. Electronic structure calculations demonstrate that compared with the bandgap of the pure In36N36 system, the In34LiHiN36 system exhibits weakened antibonding and enhanced bonding interactions, with the conduction band shifting downward more remarkably than the valence band, resulting in the narrowest relative bandgap. Optical property calculations indicate that the absorption spectrum of the In34LiHiN36 system exhibits a redshift, with the strongest photon absorption capability in the infrared region. The infrared spectral response extends to the mid-infrared region at 8 μm. These findings provide valuable insights into the application of InN-based semiconductors in infrared thermophotovoltaic cells, infrared photodetectors, and infrared semiconductor lasers. This study also serves as a guiding reference for research on the photovoltaic properties of related semiconductors.

Nitrogen-rich heterocycles are attractive candidates for next-generation energetic materials because they can deliver high heats of formation while producing relatively benign, N2-rich decomposition products. In this work, three nitrogen-rich frameworks 3,6-bis(tetrazol-5-yl)−1,2,4,5-tetrazine (H2BTTz), 2,4,6-tris(tetrazol-5-yl)−1,3,5-triazine (H3TTT), and 2,3,5,6-tetra(tetrazol-5-yl)pyrazine (H4TTP) were investigated using a combined conformational sampling and density functional theory (DFT) approach. Initial conformational searches were carried out with the MMFF method, and the lowest-energy structures were optimised at the DFT/B3LYP/6-311++G(d,p) level a widely used compromise between accuracy and computational cost for nitrogen-rich energetic molecules. Electronic structure analyses included frontier molecular orbitals, Mulliken and natural population charges, and molecular electrostatic potential maps. Energetic performance was evaluated through heats of formation, detonation velocity and pressure, and impact sensitivity estimates. Topological descriptors such as ELF, LOL, and NCI were analyzed using Multiwfn program. The calculated HOMO – LUMO gaps (3.54-4.90 eV) indicate electronically stable molecular frameworks. Gas-phase formation enthalpies were converted to condensed-phase values using a sublimation correction, and detonation properties were estimated via the Kamlet–Jacobs equations. The predicted performance follows the order H4TTP > H2BTTz > H3TTT. Although their detonation performance is lower than that of FOX-7 and CL-20, these nitrogen-rich systems remain promising candidates for reduced-sensitivity energetic materials and merit further experimental investigation.

Benzothiadiazole (BT)-based donor–acceptor oligomers with (D-A)n and (A-D-A)n architectures were synthesised through direct arylation polymerisation under both conventional and microwave-assisted conditions. The conventional heating method produced oligomers with higher degrees of polymerisation and more significant bathochromic shifts in their absorption spectra. Conversely, the microwave approach yielded lower molecular weights but provided faster reaction times, lower energy consumption, and reduced solvent use. NMR and IR spectroscopy confirmed the structures, while GPC, UV-Vis, and cyclic voltammetry revealed clear relationships between chain length, optical band gap (1.6–2.0 eV), and electronic structure. TD-DFT calculations accurately reproduced the experimental trends and demonstrated delocalisation of frontier orbitals and efficient intramolecular charge transfer. Global reactivity descriptors affirmed the donor-dominated character of these systems, while nonlinear optical (NLO) calculations indicated that polarizability and hyperpolarizability values were two to three orders of magnitude higher than those of urea. These findings suggest that short oligomers (DP = 3–4) already mimic the optoelectronic and NLO properties of longer chains, offering a strategic approach for designing π-conjugated materials for optoelectronic and photonic applications.

In molecular dynamics, conventional atomistic models of metals fail to respond to ionic environments, whereas quantum calculations are accurate but computationally expensive. Here, a simple yet accurate two-point all-atom polarisable model of silver is developed capable of instantaneous induced-charge effects. This model contains a positive silver atom, and a negative virtual site attached to the core via spring, allowing rotation and harmonic motion. The site represents the electron cloud around the metal atoms and responds to the charges in strong coherence with the classical image potential. The energy equation of the model encompasses two non-bonded and one bonded contributions. The parameters developed are not merely empirical fitting but follow the periodic trend. The model was tested to reproduce lattice parameters, density, surface energy, water interfacial energy and mechanical properties in consistency with the experimental results. Further, nanoindentation was performed on [100], [110] and [111] surfaces, producing results complying with Hertz theory. To examine its response to organic compounds, benzene was adsorbed onto three facets; computed adsorption and coverage exploration were in excellent agreement with the experiments. Robust ready-to-use model (consistent with PCFF and CVFF) is useful for interfacial studies. Besides, a comprehensive summary of earlier models of metals is also reported.

Scattering processes can be highly sensitive to the orientation of collision partners. Preparing the colliders in an initially oriented state and probing the state-resolved orientation of collision products offers up one of the richest pictures of the underlying scattering dynamics. We have previously shown how a Stark decelerator can produce ND3 molecules oriented or aligned to an external electric field, quantified using THz transitions. Here, we investigate a more convenient approach: resonance-enhanced multiphoton ionisation with variable laser polarisation to probe the m j -composition of molecules emerging from the decelerator. We derive the two-photon absorption polarisation sensitivity, generalising the work of Mo and Suzuki [J. Chem. Phys. 109, 4691 (1998)] to include elliptical polarizations. With this framework, we identify transitions maximally sensitive to the m j -composition, enabling high-fidelity probing of m j -populations. We show that j | k | ± = 1 1 − ND3 molecules can be prepared selectively in m j = 1 or 0 levels with near-unity purity across a wide velocity range. Together, this work represents a crucial step towards performing scattering measurements with velocity- and orientation-control over molecules prior to the collision, while probing how the degree of orientation evolves during the collision process.