Excited state intramolecular proton transfer emission in bent core liquid crystals

The visible light emissive bent-core liquid crystals (C56H67NO9 and C55H65NO9) are attractive candidates for high-temperature LCD and sensing applications. [Display omitted] •Photophysics of two bent core liquid crystals (C56H67NO9 and C55H65NO9) were studied.•With increasing solvent polarity, a hypsochromic shift is observed in the absorption and fluorescence spectra of the BLCs.•Dipole moments of the both liquid crystals are lower in the excited state than that of the ground state.•Out of the two tautomeric forms of emission (keto- and enol-) the keto-emission was intense.•Longer decay lifetime is associated with the vibrational states of the molecule. We report the photophysics of two bent-core liquid crystals (BLCs), C56H67NO9 (BLC1) and C55H65NO9 (BLC2), containing a Schiff-base and two long alkyl chains at its two ends. The ground state dipole moment and the electronic structures of the BLCs were calculated using density functional theory (DFT). The dipole moments of the liquid crystals were estimated experimentally via solvatochromic shift of the absorption and fluorescence spectra. The dipole moments obtained experimentally are in quite good agreement with theoretically calculated values. In the fluorescence spectra of both the BLCs show an interesting feature, i.e., dual emission. This dual emission is explained via the presence of two tautomeric forms (keto and enol) of the BLCs in the excited state. The band at ∼390–450 nm is assigned to the emission due to the keto-form, whereas the band at ∼340–370 nm is due to the emission from the enol-form. Irrespective of the solvents used, the keto-band is more intense than the enol-emission-band. This intense emission from the keto-form of the tautomers is demonstrated via the excited state intramolecular proton transfer (ESIPT). From the time resolved fluorescence spectroscopy studies, a longer lifetime is obtained for the keto-band. The associated vibrational states observed in the emission spectrum are responsible for this longer lifetime. Our finding of the dual emissive nature of the liquid crystals in the visible range is potentially useful for high temperature liquid crystal display and sensing applications.