Effect of temperature on the spectral characteristics of 2-(4′-N,N-dimethylaminophenyl)imidazo[4,5-b]pyridine

The photophysical behaviors of 2-(4′-N,N-dimethylaminophenyl)imidazo[4,5-b]pyridine (DMAPIP-b) were studied as a function of temperature in six different solvents (cyclohexane, acetonitrile, ethanol, methanol, 1-proponal and glycerol), using absorption, steady-state emission and time-resolved fluorescence techniques. The temperature strongly affects the fluorescence quantum yields and life times of both TICT and normal emissions of DMAPIP-b. Density functional theory (DFT) calculations have been performed on all two isomers of DMAPIP-b. Solvent stabilization effects have also been studied based on integral equation formalism-polarizable continuum (IEF-PCM) model in four different solvents, cyclohexane, acetonitrile, ethanol and methanol. The calculations suggested that isomer I is more stable than isomer II of all these solvents. Both solvatochromic and thermochromic methods were used to calculate the dipole moment of the TICT state and the values obtained by both methods are in good agreement with each other.

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► Temperature and viscosity affect the protic solvent induced dual emission.
► Large dipole moment calculated for the ICT state confirms that it is a TICT state.
► The formation of TICT state from LE state is dominant over the reverse process.
► The rise in temperature shifts the equilibrium toward TICT that enhances ϕfTICT/ϕfN.
► But in methanol ϕfTICT/ϕfN decreases due to enhanced nonradiative decay from TICT.