Photophysical properties of oligophenylenes end-capped with naphthyls in solution and solid state

Naphthyl-terminated oligophenylenes (DNpOPhs) were investigated to clarify how substitution topology and π-conjugation length regulate excited-state properties in linear aromatic systems. A comprehensive photophysical analysis by combining steady-state and time-resolved spectroscopy in solution and the solid state reveals pronounced <i>para</i>-<i>meta</i> contrasts in absorption spectra, fluorescence efficiencies, and radiative rates. <i>Para</i>-DNpOPhs exhibit high fluorescence quantum yields and enhanced radiative rates, <i>k</i>_f whereas <i>meta</i>-analogues show blue-shifted spectra and reduced oscillator strengths due to localized frontier orbitals. All compounds display deep-blue emission, with solid-state spectra red-shifted relative to solution, and phosphorescence enabling determination of triplet energies localized on the terminal naphthyl units. TD-DFT calculations reproduce the experimental trends, demonstrating a linear correlation between computed oscillator strengths, <i>f</i> and measured <i>k</i>_f in solution, consistent with the Strickler-Berg relationship. In the solid state, however, <i>k</i>_f saturates at ∼5 × 10⁸ s^-1 for molecules with large <i>f</i>, indicating that intermolecular interactions impose an upper limit on the effective radiative rate in the condensed phase. These results provide mechanistic insight into how intrinsic electronic structure and condensed-phase effects jointly define emission behavior, offering design principles for deep-blue emitters and related aromatic chromophores.