Solvent free synthesis and spectral analysis of 2,4-dimethyl-6-(1-phenyl-1H-benzimidazol-2-yl)phenol: on/off fluorescence, inter and intramolecular hydrogen bonding.

2,4-dimethyl-6-(1-phenyl-1H-benzimidazol-2-yl)phenol (DPBP) has been prepared and characterized by 1H NMR, 13C NMR, mass spectral studies and elemental analysis. DPBP shows On/off fluorescence system (fluorescence enhancing and quenching) by tuning with Fe3+ metal ion and H3PO4. Addition of Fe3+ ions into DPBP results in quenching of fluorescence. Other cations, including Zn2+, Ni2+, Pb2+, Ca2+, Co2+, Cd2+ and Mg2+ had little effect in the fluorescence intensity. The addition of H3PO4 with Fe3+-DPBP complex results in the enhanced fluorescence due to the detachment of Fe3+-DPBP complex. Dual emission has been observed by DPBP in non-polar solvent medium whereas single emission was observed in polar solvents due to Intra and Intermolecular hydrogen bonding respectively. Shorter wavelength emission of DPBP is due to enol rotamer and longer wavelength emission of DPBP is due to keto rotamer. [ABSTRACT FROM AUTHOR]