Fluorescence resonance energy transfer from a bio-active imidazole derivative 2-(1-phenyl-1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)phenol to a bioactive indoloquinolizine system

Novel donor imidazole derivative, 2-(1-phenyl-1H-imidazo [4,5-f][1,10]phenanthrolin-2-yl)-phenol (PIPP) was screened as highly sensitive chemisensor for transition metal ions and it can be used as a “multi-way” optically switchable material. Solvatochromic effects on the fluorescence behaviour of PIPP were studied in different solvents. The fluorescence of PIPP was highly sensitive to both the polarity as well as protic nature of the solvent. Fluorescence (Forster) resonance energy transfer (FRET) process from PIPP to a potent bioactive indoloquinolizine molecule was studied and it is argued that long-range dipole–dipole interaction is operating for the energy transfer mechanism. The energy transfer efficiency (E) and the distance between the acceptor and the donor (r0) have been determined.

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► Chemosensor—Quenching in fluorescence by Co2+ indicates the complexation of PIPP with Co2+.
► FRET—Emission band of donor and acceptor are close – isoemissive point is not possible.
► Excited state dipole moment—μe > μg supports that the excited states of PIPP is more polar than ground state.
► Energy transfer efficiency—KSV and R0 suggest that dipole–dipole interaction is responsible for energy transfer.
► Forester's distance—r (1.8 nm) < 8 nm indicates that the energy transfer occurs with high probability.