Synthesis and photophysical properties of benzimidazoles grafted pyrazole-containing pyrene or fluorene moiety: A combined spectroscopic and computational study

Herein, eight novel benzimidazoles grafted pyrazole-containing pyrene or fluorene moiety were synthesized. The substituent and solvent effects on the photophysical properties of the compounds have been analyzed based on their absorption and fluorescence bands in various solvents and the analysis was further supplemented by computational studies. The synthesized benzimidazoles derivatives show blue state emission in the range of 409–536 nm. Experimental absorption and emission wavelengths measured for all the synthesized benzimidazoles derivatives are in good agreement with those predicted using the Time-Dependent Density Functional Theory. The emission maxima of the methyl substituted compounds 6a-d increased compared to that of the unsubstituted derivatives 5a-d. However, upon methyl substitution the system undergoes fluorescence quenching. Computational analyses are used to understand the mechanism behind the fluorescence quenching and are helpful in explaining the electronic behavior of the chemical species reported here.