Transmittal Effect Evaluation of Heterocyclic Rings on Nonlinear Optical Ambit of Benzotrithiophene-Based Push-Pull Driving Materials: a Theoretical Approach

To obtain extensive insights into NLO properties, herein, two series of benzotrithiophene (BTT) based organic compounds (MS1-MS5 and MP1-MP5) containing D₁-π₁-D₂-π₂-A-type framework have been designed. The structural tailoring was accomplished via the incorporation of thiophene and pyrrole units in MS1-MS5 and MP1-MP5, respectively at the region of π₂ in each derivative. Quantum chemical calculations including: frontier molecular orbitals (FMOs), natural population analysis (NPA), UV-Vis investigation, transition density matrix (TDMx), density of state (DOS), molecular electrostatic potential (MEP) and natural bond orbitals (NBOs) analyses were accomplished at MPW1PW91/6-311G(d,p) functional to determine the influence of π-linkers on the optical response of designed chromophores. Conclusively, remarkable NLO results were obtained for thiophene-based derivatives (MS1-MS5) as compared to pyrrole-based derivatives (MP1-MP5). Interestingly, among all the derivatives, minimum E gap values of 2.248 and 2.264 eV were observed for MS4 and MS5, respectively, and the E gap values were found in the following decreasing order: MS1>MS3>MS2>MS5>MS4. Surprisingly, MS4 and MS5 displayed maximum amplitudes of < α> i.e., 2.44 × 10⁻²² and 2.65 × 10⁻²²esu as well as < γ> such as: 3.91 × 10⁻³² and 4.35 × 10⁻³²esu, respectively. Moreover, the declining trend of < γ> was observed as follows: MS5 > MS4 > MS2 > MS3 > MS1. In a nutshell, this investigation may provide a new insight for the use of these BTT-based organic chromophores especially MS4 and MS5 for potential NLO-based hi-tech applications.