Quantum technologies are moving from conceptual demonstrations toward functional systems for computation, communication, sensing and information processing. This transition requires materials capable of generating, preserving, controlling and transporting electronic, spin and optical quantum states. Discovering materials exhibiting accessible and controllable quantum phenomena is therefore fundamental to advancing quantum technologies. Two-dimensional layered quantum semiconductors provide a promising platform for hosting and enhancing quantum-mechanical phenomena that are absent, weak or experimentally inaccessible in conventional bulk semiconductors. Although quantum theory predicts a rich spectrum of such phenomena in two-dimensional semiconductors, many remain experimentally unrealized or have not been directly observed. Moreover, the microscopic relationships connecting atomic structure, electronic wavefunctions and technologically relevant quantum functionality remain insufficiently understood. Addressing this gap requires a systematic theoretical approach beginning with the design and discovery of materials in which technologically relevant quantum phenomena are intrinsically enhanced and experimentally accessible. Accordingly, the central purpose of this project is to reveal how quantum degrees of freedom emerge, interact and can be controlled in newly designed two-dimensional organic–inorganic perovskite semiconductors, and ultimately to translate this understanding into viable material concepts for next-generation quantum technologies. Layered organic–inorganic perovskites are particularly attractive because their chemically tunable architecture provides exceptional freedom to engineer the atomic structure and electronic environment governing spin polarization, spin–momentum coupling, quantum and dielectric confinement, excitonic behavior, charge localization and other technologically relevant quantum properties. The theoretical investigation will identify the most significant properties of promising material candidates and determine how they can provide useful functionality for emerging quantum technologies. Density functional theory (DFT) will be used to design and discover promising 2D semiconductors and investigate their ground-state quantum properties, while time-dependent density functional theory (TDDFT) will be employed to study selected optical, excited-state and dynamical phenomena. New layered perovskite structures will be designed through systematic variation of their organic and inorganic building blocks, followed by structural relaxation, stability assessment and electronic-structure screening using Quantum ESPRESSO. Because predictive reliability depends strongly on the theoretical approximation employed, the computational approach will be selected according to the property under investigation. The generalized gradient approximation (GGA), particularly the Perdew–Burke–Ernzerhof (PBE) functional, will support structural optimization and initial electronic-structure screening. Because conventional GGA inadequately describes long-range interactions between organic and inorganic layers, van der Waals dispersion corrections will be incorporated to obtain reliable interlayer geometries, binding interactions and electronic structures. For materials containing heavy elements, fully relativistic pseudopotentials, non-collinear spin formalism and spin–orbit coupling will describe relativistic band modifications and spin-dependent quantum phenomena. Where conventional DFT is insufficient, advanced exchange–correlation or quasiparticle corrections will be selectively introduced. TDDFT will describe optical excitations and responses to time-dependent electromagnetic fields, while real-time TDDFT will follow photoinduced charge redistribution and ultrafast non-equilibrium electronic dynamics.