Photophysical Behavior and Computational Investigation of Novel 1,4-Bis(2-(2-Phenylpyrimido[1,2-a]Benzimidazol-4-Yl)Phenoxy)Butan (BPPB) Macromolecule.

A new macromolecule pyrimido[l,2-a]benzimidazole derivative named 1,4-bis(2-(2-phenylpyrimido[1,2-a]benzimidazol-4-yl)phenoxy)butan (BPPB) has been synthesized in accepted yield using microwave assistance. The new compound BPPB has been formed by the interaction of 3,3'-((butane-1,4-diylbis(oxy))bis(2,1-phenylene))bis(1-phenylprop-2-en-1-one) (3) with 2- aminobenzimidazole (4) in the presence of potassium hydroxide as a basic catalyst in dimethylformamide (DMF) under microwave radiation for 20 min. The chemical structure of this novel compound was elucidated by elemental and spectral techniques including: FT-IR, (1)H-NMR, (13)C-NMR and mass spectra. The electronic absorption and emission spectra of BPPB were measured in different solvents. BPPB displayed a solvatochromic effect of the emission spectrum that is reflected by red shifts of its fluorescence emission maxima on increasing the solvent polarity, indicating a change of electronic charge distribution upon excitation. BPPB crystalline solids gave excimer-like emission at 535 nm with a bandwidth of ca. 60 nm. Ground and excited states electronic geometry optimizations using density functional theory (DFT) and time-dependent density functional theory (TD-DFT), respectively, complemented these spectral findings. The intramolecular charge transfer was investigated by natural bond orbital (NBO) technique.