1,10-Phenanthrolines with tunable luminescence upon protonation: a spectroscopic and computational study

Area of Science:

• Organic Chemistry
• Photophysics
• Materials Science

Background:

• 1,10-phenanthroline derivatives are versatile ligands and luminescent materials.
• Understanding structure-property relationships is crucial for designing new functional molecules.

Purpose of the Study:

• To synthesize and characterize nine 2,9-aryl-substituted 1,10-phenanthrolines.
• To investigate their electronic absorption and luminescence properties in both neutral and protonated states.
• To explore their potential application as proton sensors.

Main Methods:

• Synthesis of nine 2,9-aryl-substituted 1,10-phenanthroline derivatives.
• UV-vis absorption and 1H NMR spectroscopy to confirm protonation.
• Spectrofluorometry to study luminescence properties.
• Time-dependent Hartree-Fock and density functional theory calculations to rationalize spectral data.

Main Results:

• Three distinct groups of phenanthrolines were identified based on luminescence behavior.
• Protonation of phenanthrolines led to significant changes in absorption and fluorescence spectra (color tuning).
• Vapoluminescence was observed in solid-state films upon exposure to acid vapors, indicating proton sensing capabilities.

Conclusions:

• The electronic and luminescence properties of aryl-substituted phenanthrolines are highly dependent on their structure and protonation state.
• These compounds exhibit tunable emission, making them promising candidates for solid-phase proton sensors.