Nonlinear optical properties and spectroscopic analysis of NB-pyrrole isosteres: Theoretical investigation

The nonlinear optical properties and spectroscopic analysis of mono and double NB-substituted pyrrole, namely: PN3B2 PN3B4 PN2B3 PN2B4 PN3,4N2,5, and PN2,5B3,4 have been investigated using two levels of theory: MP2/6-311+G (2df,2p) and DFT B3LYP/6-311++G(d,p). The vibrational spectra spam the range of 400 - 4000 cm- 1, where each structure possesses 9 stretching, 8 bending, and 7 torsions modes, with only CH vibrational modes appeared in the mono-substituted group. The energy gap of the mono-substituted group is generally lower than that the double-substituted one. The most stable PN3B2 and PN3,4B2,5 isosteres show the maximum excitation energy and blueshift wavelengths. In solution, the bands are redshifted. The largest chemical shifts for the PN3B4 isostere's NH1 and BH1 protons are found at 8.5 and 4.8 ppm, respectively. The polarizability improves linearly as a function of the dipole moment. The PN2B4 introduces the highest dipole moment and consequently the polarizability, while PN3B2 shows opposite trend.