Counter anion effect on structural, opto-electronic and charge transport properties of fused π-conjugated imidazolium compound
The structure–activity relationship of fused π-conjugated imidazolium cation with three counter anion molecules, BF4−, CF3SO3− and (CF3SO2)2N−, was studied using electronic structure calculations. The structural, opto-electronic and charge transport properties of these complexes were studied. The charge transfer from π-conjugated imidazolium(I) to counter anion was confirmed in all the studied complexes. Interaction energy varies significantly depending on the counter anion and the stability was found higher for I-BF4 complex than both I–CF3SO3 and I–(CF3SO2)2N complexes. The strong (C–H)+···F− hydrogen bond of length 1.95 Å between fused π-conjugated imidazolium and BF−4 anion is the driving force for the strongest interaction energy in I–BF4 complex. The energy decomposition analysis confirms that the interaction between imidazolium and counter anion is mainly driven by electrostatic and orbital interaction. It has been observed that the absorption spectra of the complex are independent of anion nature but the influence of anion character is observed on frontier molecular orbital pattern. The charge transport property of I–BF4 complex was studied by using tight-binding Hamiltonian approach and found that the hole mobility in I–BF4 is 1.13 × 10−4 cm2 V−1 s−1.