Excited-State Dynamics and Energy-Transfer Pro- Cesses in Advanced Organic Semiconductors

This thesis investigates the excited-state dynamics and energy transfer mechanisms in organic molecular systems, emphasizing how chemical structure, environment, and photonic confine- ment govern their photophysical behavior. A combination of steady-state spectroscopy, time- resolved fluorescence, and transient absorption or reflectance measurements was employed to correlate molecular architecture with radiative and non-radiative decay pathways. Spiro- bridged triphenylamine derivatives (FTN-H and FTN-(CN)6) were examined to understand how electron-withdrawing cyano substituents and solvent polarity modulates charge-transfer (CT) character and excited-state relaxation. Comprehensive studies across different solvents and ox- ygen conditions indentified distinct photophysical pathways, including possible evidence for thermally activated delayed fluorescence (TADF) FTN-(CN)6. The investigation then focused on octaazadibenzocd,lmperylene-2,9-dione (OAPPDO) derivatives in solution and thin-film phases. While all compounds exhibited high fluorescence quantum yields in solution, solid- state measurements uncovered additional channels including aggregate formation and triplet generation via singlet fission (SF). Morphology-dependent dynamics revealed that crystalline films proceed through excimer intermediates, whereas amorphous systems undergo more direct SF pathways, with varying triplet formation efficiencies influenced by molecular packing. Fi- nally, integrating OAPPDO VII into Fabry-Pérot microcavities demonstrated dynamic control of emission properties thorough photonic confinement. Cavity thickness systematically modu- lated fluorescence lifetimes via the Purcell effect acceleration, with the thinnest configuration achieving weak coupling and suppressing triplet formation by accelerating singlet radiative de- cay. Together, these results stablish that strategic manipulation of molecular design, environ- mental conditions, and photonic architectures provides precise control over energy transfer pro- cesses, critical for advancing organic optoelectronic and energy-conversion technologies.