Study of optical and nonlinear optical properties of symmetric/asymmetric benzo[d]oxazole derivatives under gas and solvent solute interaction models

The oxazole class of organic compounds exhibits remarkable versatility, offering applications across a wide array of scientific and technological domains. In this current investigation we designed eight different derivatives of the benzo[d]oxazole (BOZ) class with different donor and acceptor groups substitutions named BOZ-1 to BOZ-8. Density functional theory (DFT) calculations are conducted, employing the M06/6-311G* level of study to determine the linear polarizability (alpha) and third-order NLO polarizability (<gamma>) of the system. For BOZ-5, the isotropic linear polarizability (alpha(iso)) and anisotropic linear polarizability (alpha(aniso)) are calculated to be 90.52 x 10(-24) esu and 147.4 x 10(-24) esu respectively. Comparative analysis shows that BOZ-5 exhibits the highest value of <gamma > amplitude, calculated to be 2844 x 10(-36) esu. This increase in <gamma > amplitude in BOZ-5 is due to the strategic placement of (N(CH3)(2)) groups in the molecule and D-pi-D configuration, which leads to maximum delocalization of electrons within the molecule. To study the influence of solvents on alpha and < gamma>, advanced computational approaches such as polarizable continuum model (PCM) and the conductor-like screening model (COSMO) are employed to simulate both polar and non-polar solvent environments. When modeled in the COSMO-CH3OH environment, the alpha(iso) and < gamma > amplitudes of BOZ-5 show values of 116.3 x 10(-24) esu and 5575 x 10(-36) esu, respectively, reflecting a notable similar to 2-fold increase in <gamma > amplitudes compared to their gas-phase counterparts. Furthermore, we performed dynamic <gamma > response calculations to investigate the phenomenon of resonance enhancement using the dc-Kerr Effect and Electric Field-Induced Second Harmonic Generation (EFISHG) techniques. Time-dependent DFT calculations revealed that BOZ-5 exhibits the highest <gamma > amplitude (2844 x 10(-36) esu) and the lowest transition energy (3.02 eV) for the HOMO-LUMO transition among all compounds. A reduced orbital energy gap of 3.11 eV, along with electron density difference maps, molecular electrostatic potential diagrams, and density of state analysis, further supports that BOZ-5 exhibits the strongest intramolecular charge transfer (ICT) properties among all the designed compounds. In the assessment of photovoltaic parameters, it becomes evident that BOZ-5 stands out with the highest open circuit voltage (V-oc) value recorded at 1.65, alongside the lowest Delta G(reg) value of 0.67 eV.