Studying the influence of electron donor-withdraw groups on the photophysical properties of 3-arylthioimidazo[1,2-a]pyridines: experimental and theoretical study

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Imidazo[1,2-a]pyridine derivatives have received great attention in recent years in various fields such as pharmaceuticals and material sciences, to a lesser extent, thanks to the great flexibility to incorporate different peripheral groups. With the advance in chemical synthesis routes, a large number of substituted imidazo[1,2-a]pyridines have been developed but are still to be investigated as new optical materials. Therefore, we performed a spectroscopy study for a set of nine substituted 3-arylthioimidazo[1,2-a]pyridine derivatives with different peripheral groups to reveal their structure-optical property relationships and gain a deeper understanding of the influence of the nature of the substitution. The photophysical measurements include linear absorption, fluorescence emission, quantum yield, fluorescence lifetime, anisotropy and solvatochromism. The results showed that these optical properties can be modulated by changing the position and/or nature of the peripheral groups. For example, the fluorescence quantum yield values can increase c.a. ten-fold, which is vital for fluorescent applications, and the permanent dipole moment difference at the first excited state (Δμ01) increased c.a. five-fold. Moreover, the performance of quantum chemical calculations using the Density Functional Theory and a polarisable continuum solvation model allowed us to understand the electronic transitions and charge transfer of the derivatives investigated.