This thesis develops a microscopic theory of open quantum dynamics for coupled molecular emitters with excitation-dependent permanent dipoles. In many standard excitonic models, intermolecular interactions are characterised only by transition dipoles. This work shows that such an approximation can miss an important set of electrostatic couplings arising from state-dependent permanent dipoles, which reshape collective eigenstates and modify both radiative and non-radiative relaxation pathways. The thesis focuses on a minimal molecular dimer model interacting with photonic and vibrational environments, with the aim of understanding how static dipoles alter dark-state formation, optical spectra, and the validity of commonly used reduced-dynamics methods.

A static-dipole-consistent microscopic Hamiltonian is first formulated in the multipolar gauge. Using this model, it is shown that excitation-dependent permanent dipoles can generate, destroy, or stabilise dark and near-dark states by modifying the effective transition dipoles between eigenstates. In particular, permanent-dipole-induced interference introduces forms of radiative suppression and disorder robustness that are absent from transition-dipole-only descriptions. The model is then extended to vibrational environments that act through multiple channels, including energy modulation, geometry-dependent electrostatic coupling, and dipole modulation. This reveals the interplay of different vibrational modes with static dipoles.

To treat a stronger vibronic dressing, an eigenbasis polaron formulation is developed, clarifying the roles of reorganisation energy, displaced bath correlations, and the resulting absorption-emission asymmetry. Finally, the thesis develops an self-dressed propagator master equation strategy based on the Nakajima-Zwanzig formalism for regimes in which the Born approximation becomes unreliable due to more structured environments. Together, the results show that excitation-dependent permanent dipoles have a physically significant effect on the open quantum dynamics of coupled emitters and provide a framework for studying their consequences across different environmental coupling regimes.