Simulazione di materiali liquido cristallini a fluorescenza ritardata attivata termicamente

In this thesis, we investigate the organic compound 2,5-Bis-(3,6-di-(3,4-didodecyloxyphenyl)carbazolyl)-1,4-dicyanobenzene (C3B), a material classified as a TADF-OLED (thermally activated delayed fluorescence organic light-emitting diode) compound. Experimentally, C3B has been shown to exhibit a hexagonal columnar liquid crystal mesophase with an isotropic melting point of 454 K [1]. Our study employs two main computational approaches: molecular dynamics (MD) and time-dependent density functional theory (TD-DFT). These methods are used to investigate both the morphology of the columnar phase and the optical properties of the compound, with a particular focus on the S₁ → S₀ and S₁ ⇌ T₁ transitions. We began with MD simulations using NAMD modeling, a system of 180 molecules. Our computational model was validated by comparing the results with experimental data from [1]. The simulations confirmed that the system forms a columnar phase, with a stacking distance comparable to experimental values, and that the columns adopt a quasi-hexagonal close-packed arrangement. Once the reliability of the model was established, we proceeded with DFT benchmark calculations using ORCA to analyse the absorption and emission spectra of C3B, comparing them to experimental data in toluene [2]. We tested four functionals—PBE0, M06, CAM-B3LYP, and B2GP-PLYP—before narrowing our focus to PBE0 and CAM-B3LYP, as M06 and B2GP-PLYP showed a less favorable balance between accuracy and computational cost. Finally, we used DFT to explore the impact of columnar aggregation on the TADF process. Specifically, we analysed molecular pairs extracted from MD simulations, comparing their absorption and emission spectra to those of isolated dimers. Our findings demonstrate strong agreement between our computational results and experimental data. [1] DOI 10.1039/d1tc00443c [2] DOI 10.1039/d2cp02684h