Quantum Study of Halogen Substituted anti-B18H22 Borane Clusters for Optoelectronics

Abstract: We offer a quantum chemical analysis of mono-halogenated borane molecules using DFT and TD-DFT theories, applying the PBE0/def2-SVPD and B3LYP/6-311+G(d) methods as implemented in ORCA, and explore how solvent effects influence electronic transition properties. The comparable benchmarks are the archetype anti-\ce{B18H22} denoted as (1) against hypothetical halogenated derivatives: 7-F-anti-\ce{B18H21} (2), 4-F-anti-\ce{B18H21} (3), and the recently synthesized 4-Br-anti-\ce{B18H21} (4). The analysis includes an optimization of the ground and first singlet excited states, vibrational frequency analysis, and a comprehensive spectroscopic profile covering IR, Raman, UV-Vis absorption, and emission spectra. The IR spectra of the fluorinated compounds feature a characteristic B-F stretching peak, while the Raman spectra closely resemble the parent molecule. UV-Vis spectral analysis shows a redshift and oscillator strength enhancement for F at position B7, indicating altered electronic properties due to substitution with lighter halogen. Furthermore, solvent effects enhance the probability of electronic transitions. Halogene presence led to a decrease of the energy gap EG(LUMO-HOMO) due to the stabilization of LUMO, which implied a redshift in the emission/absorption wavelength spectra, with the largest EG change at around 14\% occurring for the (4)$<sup>{th}$ benchmark compound.. Notably, all compounds emit light within the visible spectrum, underscoring their potential for optoelectronic applications.