Theoretical Perspective toward Designing of 5-Methylbenzo [1,2-b:3,4-b':6,5-b″] trithiophene-Based Nonlinear Optical Compounds with Extended Acceptors.

A series of benzotrithiophene-based compounds (DCTM1-DCTM6) having D(1)-π(1)-D(2)-π(2)-A configuration were designed using a reference molecule (DCTMR) via incorporating pyrrole rings (n = 1-5) as the π-spacer (π(2)). Quantum chemical calculations were performed to determine the impact of the pyrrole ring on the nonlinear optical (NLO) behavior of the above-mentioned chromophores. The optoelectronic properties of the compounds were determined at the MW1PW91/6-311G(d,p) functional. Among all of the derivatives, DCTM5 exhibited the least highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) band gap (E(g)) 0.968 eV with a high softness of 0.562 eV(-1), and hence possessed the highest polarizability. Interestingly, transition density matrix (TDM) findings demonstrated that DCTM5 with an effective diagonal charge transmission proportion at the acceptor group supports the frontier molecular orbital (FMO) results. Additionally, the exciton binding energy values for DCTM1-DCTM6 were found to be less than that for DCTMR and thus, the effective charge transfer was examined in the derivatives. All of the derivatives exhibited effective NLO outcomes with the highest magnitude of linear polarizability ⟨α⟩, and first (β(tot)) and second (γ(tot)) hyperpolarizabilities relative to the parent compound. Nevertheless, the highest β(tot) and γ(tot) were obtained for DTCM1 and DTCM6, 7.0440 × 10(-27) and 22.260 × 10(-34) esu, respectively. Hence, through this structural tailoring with a pyrrole spacer, effective NLO materials can be obtained for optoelectronic applications.