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Abstract

In optical microcavities, strong light–matter coupling gives rise to exciton polaritons, hybrid light–matter states formed through the interaction between confined photons and molecular excitons. While the criteria for achieving strong coupling are well established, the influence of molecular properties on lower polariton (LP) population and polariton-mediated energy transfer remains underexplored. This thesis investigates the potential of N-heteropolycycle-based systems as versatile platforms for strong light–matter coupling in organic microcavities, aiming to deepen in- sight into exciton–polariton phenomena in molecular materials. Three primary objectives were pursued. First, the viability of N-heteropolycycles for polariton formation was estab- lished using thioether-functionalized tetraazaperylene (TFTAP) derivatives (Butyl-, Benzyl- , and p-methoxybenzyl (PMB)-TFTAP) embedded in polystyrene matrices within metal- clad microcavities. Angle-resolved reflectivity and photoluminescence (PL) spectroscopy confirmed polariton formation, with Rabi splitting energies ranging from 40 to 241 meV— comparable to established organic systems. Polariton properties were tuned via cavity thick- ness and emitter concentration, validating the collective and coherent nature of the coupling. Second, polariton relaxation pathways in vibronically active tetraazacoronene (TAC) trimer systems were explored, revealing detuning-dependent contributions from radiative pump- ing (RP) and vibrationally assisted scattering (VAS). Spectral signatures indicated that reso- nance between states and vibronic or Raman-active modes enhances LP population, offering mechanistic insights relevant to low-threshold polariton lasing. Third, polariton-mediated energy transfer was investigated in multilayer microcavities incorporating donor–acceptor pairs (ATTO 680–IRDye and ATTO 655–IRDye). Systems with larger exciton energy off- sets exhibited enhanced acceptor emission due to modulation of polariton composition, es- tablishing energy offset as a key parameter for efficient energy transfer design.