LE and ICT properties of pyrazolo[1,5-a]pyrimidines based dyes: Experiments and DFT/TDDFT calculations

Several pyrazolo [1,5-a]pyrimidine dyes 4a-f were synthesized and treated with triethylorthoacetate to give new pyrazolo [(Thumar et al., 2016; Asati et al., 2021) 1,51,5-a]pyrimidine-2,5-diyl]diacetimidate dyes 5a-f. The structures have been fully characterized by H-1, C-13 NMR and FT-IR and elemental analysis. The tunable photophysical properties of all the dyes have been investigated using a combination of experimental (UV-Visible and PL) spectroscopy and theoretical (DFT and TDDFT) calculations. These materials act as push-pull D-p-A systems with different electron donating and electron withdrawing groups. Good agreement has been found between experimental and theoretical UV-Vis absorption characteristics. The addition of triethylorthoacetate gave interesting and motivating results. In particular, the Intramolecular Charge Transfer (ICT) mechanism is improved, and the absorption features were redshifted by lowering the transition energy. Several dyes, mainly bearing aryl chlorides, allowed excellent solid-state emission intensities as a result of the ICT enhancement. The main results obtained are the substitution and addition of triethylorthoacetate, leading to new important emitting dyes with good stability, which could be very interesting for applications in optoelectronic devices.