Properties of Molecular Materials: the Effect of the N-H/B Substitution on the Electronic Structure of 2-Hydroxybenzaldimine.

2-Hydroxybenzaldimine belongs to the Schiff bases which are important class of the modern molecular technology. Effect of the N-H/B substitution on the electronic structure of the title compound was inspired by the pioneering work of Hargis and co-workers (J. Am. Chem. Soc., 2008, 130 (51), 17471). The DFT/B3LYP investigation included analyzing the structures, the tautomerism energies, the intramolecular charge transfer processes, the bond critical point electron densities, the infrared stretching frequencies, and the frontier orbitals. The results confirm and illustrate that boron is a powerful electron withdrawing group that can force the structure to loosing the aromatic stabilization energy and to forming the keto-tautomer as the more stable skeleton. In addition to that, this substitution has drastic consequences on the various electronic structure aspects. Among them, it can lower the molecular band gap considerably and therefore can be used as the corner stone in designing new molecular electronics and small-molecule dyes. In this regard, we report here a small conjugated π-system of a band gap equivalent to 2.42eV (TD-DFT), which is attributed to the keto-tautomer of the -BN2C2 derivative. These results can be considered as a new addition to the boron chemistry.