Design and Synthesis of Aggregation-Caused Quenching Hydroxy-Phenanthroimidazole Derivatives for Probing of Fe3+ Ions and as Potential Blue Light Emitters

Fluorescence aggregated molecules tend to employ versatile opportunities in metal ion probe sensors and fluorescent lighting. To achieve this dual challenging task, currently synthesized three phenanthroimidazole-naphthalene-based compounds Pq-tBu-OH, Pq-mF-OH, and Pq-pF-OH are derived based on substitution at N₁ position for better photophysical and electrochemical properties. Compared experimental and theoretical calculations define the highest bandgap to be 2.75 eV of Pq-pF-OH, and the same molecule expressed a higher (348 °C) thermal decomposition. The calculated singlet and triplet energies found in the range of 3.24–3.67 and 2.70–2.72 eV indicate well energy transfer from S₁→S₀ (quantum yield of 23.36 %, lifetime is 4.05 ns). Among the numerous morphologies, the solid form exhibited improved intensive deep blue emission (x=0.159, y=0.051), and its InGaN LED results demonstrated a strong deep blue emission at 418 nm. Moreover, the fluorophores were experimentally visualizing the aggregation-caused quenching (ACQ) which enables the probing of Fe³⁺ ion. However, for the first time, the ACQ-assisted concept is applied through synthesized molecules for Fe³⁺ ion probing via fluorescence spectra, Job's plot calculation, and ¹H NMR results. In addition, the probe works excellently at a detection limit of 10 μM and it could also act as a potential competitor for lighting applications.