In molecular solids, the intense photoluminescence (PL) observed for solvated dye molecules is often suppressed by nonradiative decay processes introduced by excitonic coupling to adjacent chromophores. We have developed a strategy to avoid this undesirable PL quenching by optimizing the chromophore packing. We integrated the photoactive compounds into metal-organic frameworks (MOFs) and tuned the molecular alignment by introducing adjustable “steric control units” (SCUs). We determined the optimal alignment of core-substituted naphthalenediimides (cNDIs) to yield highly emissive J-aggregates by a computational analysis. Then, we created a large library of handle-equipped MOF chromophoric linkers and computationally screened for the best SCUs. A thorough photophysical characterization confirmed the formation of J-aggregates with bright green emission, with unprecedented photoluminescent quantum yields for crystalline NDI-based materials. This data demonstrates the viability of MOF-based crystal engineering approaches that can be universally applied to tailor the photophysical properties of organic semiconductor materials.

The recent fabrication advances in nanoscience and molecular materials point toward a new era where material properties are tailored in silico for target applications. To fully realize this potential, accurate and computationally efficient theoretical models are needed for: a) the computer‐aided design and optimization of new materials before their fabrication; and b) the accurate interpretation of experiments. The development of such theoretical models is a challenging multi‐disciplinary problem where physics, chemistry, and material science are intertwined across spatial scales ranging from the molecular to the device level, that is, from ångströms to millimeters. In photonic applications, molecular materials are often placed inside optical cavities. Together with the sought‐after enhancement of light‐molecule interactions, the cavities bring additional complexity to the modeling of such devices. Here, a multi‐scale approach that, starting from ab initio quantum mechanical molecular simulations, can compute the electromagnetic response of macroscopic devices such as cavities containing molecular materials is presented. Molecular time‐dependent density‐functional theory calculations are combined with the efficient transition matrix based solution of Maxwell's equations. Some of the capabilities of the approach are demonstrated by simulating surface metal‐organic frameworks ‐in‐cavity and J‐aggregates‐in‐cavity systems that have been recently investigated experimentally, and providing a refined understanding of the experimental results.

The accurate and efficient computation of the electromagnetic response of objects made from artificial materials is crucial for designing photonic functionalities and interpreting experiments. Advanced fabrication techniques can nowadays produce new materials as 3D lattices of scattering unit cells. Computing the response of objects of arbitrary shape made from such materials is typically computationally prohibitive unless an effective homogeneous medium approximates the discrete material. In here, a homogenization method based on the effective transition (T‐)matrix, is introduced. Such a matrix captures the exact response of the discrete material, is determined by the T‐matrix of the isolated unit cell and the material lattice vectors, and is free of spatial dispersion. The truncation of to dipolar order determines the common bi‐anisotropic constitutive relations. When combined with quantum‐chemical and Maxwell solvers, the method allows one to compute the response of arbitrarily‐shaped volumetric patchworks of structured molecular materials and metamaterials.

Electronic circular dichroism is an important optical phenomenon offering insights into chiral molecular materials. On the other hand, metal–organic frameworks (MOFs) are a novel group of crystalline porous thin‐film materials that provide tailor‐made chemical and physical properties by carefully selecting their building units. Combining these two aspects of contemporary material research and integrating chiral molecules into MOFs promises devices with unprecedented functionality. However, considering the nearly unlimited degrees of freedom concerning the choice of materials and the geometrical details of the possibly structured films, urgently it needs to complement advanced experimental methods with equally strong modeling techniques. Most notably, these modeling techniques must cope with the challenge that the material and devices thereof cover size scales from Ångströms to mm. In response to that need, a computational workflow is outlined that seamlessly combines quantum chemical methods to capture the properties of individual molecules with optical simulations to capture the properties of functional devices made from these molecular materials. The focus is on chiral properties and applying work to UiO‐67‐BINOL MOFs, for which experimental results are available to benchmark the results of the simulations and explore the optical properties of cavities and metasurfaces made from that chiral material.

Shape-based coarse graining of proteins permits anisotropic intermolecular interactions modulating protein solubility. Together with the ion–protein dispersion, it allows the calculation of theB₂₂coefficients without experimental fitting.

Nonlinear optics is essential for many recent photonic technologies. Here, a novel multi‐scale approach is introduced to simulate the nonlinear optical response of molecular nanomaterials combining ab initio quantum‐chemical and classical Maxwell‐scattering computations. In this approach, the first hyperpolarizability tensor is computed with time‐dependent density‐functional theory and incorporated into a multi‐scattering formalism that considers the optical interaction between neighboring molecules. Such incorporation is achieved by a novel object: the Hyper‐Transition(T)‐matrix. With this object at hand, the nonlinear optical response from single molecules and also from entire photonic devices can be computed, including the full tensorial and dispersive nature of the optical response of the molecules, as well as the optical interaction between different molecules as, for example, in the lattice of a molecular crystal. To demonstrate the applicability of the novel approach, the generation of a second‐harmonic signal from a thin film of an Urea molecular crystal is computed and compared to more traditional simulations. Furthermore, an optical cavity is designed, which enhances the second‐harmonic response of the molecular film up to more than two orders of magnitude. This approach is highly versatile and accurate and can be the working horse for the future exploration of nonlinear photonic molecular materials in structured photonic environments.