In order to gain an understanding of the nature of the interactions among thiophene (TS), thiophene sulfone (TSO2), dibenzothiophene (DBT), dibenzothiophene sulfone (DBTO2) and the ionic liquid N-butylpyridinium hydrogen sulfate ([BPY][HSO4]), a systematic investigation has been carried out using ab initio methods. The most stable structures indicate that both [BPY](+) and [HSO4](-) play crucial roles in the interactions between TS, TSO2, DBT, DBTO2 and [BPY][HSO4]. Analyses of the most stable optimized structures suggest the occurrence of steric effects, π-π stacking effects, hydrogen bonds, and dihydrogen bonds. The π-π stacking effect in [BPY][HSO4]-TSO2/[BPY][HSO4]-DBTO2 is less significant than that in [BPY][HSO4]-TS/[BPY][HSO4]-DBT, as TSO2 and DBTO2 are more nucleophilic than TS and DBT, resulting in stronger interactions between [BPY][HSO4] and TSO2/DBTO2 than between [BPY][HSO4] and TS/DBT. Thermodynamical data also demonstrate that TSO2/DBTO2 are more prone to interact with [BPY][HSO4] compared with TS/DBT.