The effect of π-extended indoleninyl-dibenzotetraaza[14]annulenes on their third-order nonlinear optical properties

Two new dibenzotetraaza[14]annulenes (DBTAAs) featuring indolenine moieties were synthesised via an acetic acid-catalysed condensation of 1,2-diaminobenzene with two diformyl indolenines in good yields. The structural identity of the compounds was confirmed by NMR (1H, 13C), FT-IR and elemental analysis. UV-visible analysis displays intense absorptions in the Soret band region with ɛ ranging from 0.32 to 1.02 × 105 M−1 cm−1 in various solvents of different polarities. The absorption spectra display a slight bathochromic shift upon replacing the indolenine (4a) with benz[e]indolenine (4b) groups on the DBTAA framework. Furthermore, the spectra exhibit solvatochromism shifts due to hydrogen-bonding interactions between the solutes and solvents. The effect of the extended π-conjugation on the electronic distributions at different energy levels was computed by Density Functional Theory (DFT) calculations. Compound 4b exhibits greater Nonlinear Optical (NLO) parameters compared to 4a due to the extended π-conjugation in the molecule. Hence, 4b could be utilised as a promising material for various NLO applications.