A comparative analysis of the optical and nonlinear optical properties of cross-shaped chromophores: Quantum chemical approach

Using the first principles calculations, optical and nonlinear optical (NLO) properties are calculated for three crossed shaped chromophores having alike benzoic acid π-conjugated side chains but different central cores i.e. phenyl in 1-Ph, pyrazino[2,3-g]quinoxaline in 2-PyQ and tetrathiafulvalene in 3-TTF. Molecular geometries are effectively reproduced and compared to their experimental crystallographic structures. The third-order NLO polarizability is calculated with three different DFT functionals including M06, PBE0 and B3LYP using 6-311G* basis set. Our calculated third-order NLO polarizability amplitudes and their comparison to those of standard and contemporary NLO chromophores indicate that all the three compounds have remarkably larger NLO response. The γ amplitudes of compounds 1-Ph, 2-PyQ and 3-TTF are 429.6 × 10−36, 1871.7 × 10−36 and 967.5 × 10−36 esu, respectively, at M06/6-311G* level of theory. Interestingly, in present investigation the γ amplitude of the best-studied NLO compound 2-PyQ is 257 times larger than that of para nitroaniline (7.279 × 10−36 esu) at the same M06/6-311G* level of theory. The TD-DFT calculations are used to trace the origin of larger NLO response. Additionally, total and partial densities of states are calculated to compare the effect and contributions of central cores in all adopted compounds. Thus, the present investigation will not only highlight the NLO potential of entitled compounds but also provoke the interest of experimentalists to effectively modify the central cores for such other applications.