Electronic Structure and Optical Properties of Boron Difluoride Dibenzoylmethane Derivatives

Abstract

Electronic structure and optical properties of boron difluoride dibenzoylmethanate BF2Dbm and its four derivatives were studied using X-ray photoelectron spectroscopy, absorption and luminescence spectroscopy, and quantum chemistry (DFT and TDDFT). In a series of the studied compounds, the relationship of molecular design and optical properties has been revealed. At the transition from BF2Dbm to BF2Dbm(OCH3)2, the HOMO-LUMO energy gap decreases, resulting in a bathochromic shift of the optical spectra. Substitution of one methoxy group by the nitro group in BF2Dbm(OCH3)2 causes a decrease in the contribution of the chelate ring π-orbital in the LUMO, resulting in a lower value of charge transfer from the substituents to the chelate ring in the case of the first excited state, which determines the characteristics of the main absorption bands. The nitro group transition from the m- to p-position of the benzene ring causes a change in the nature of the main bands of the optical spectra due to the increase of the splitting value of the LUMO and LUMO+1 levels. The main band in the optical spectra of the complex containing the C10H7 group is associated with the charge transfer transitions.

Photophysical Properties of Phenacylphenantridine Difluoroboranyls: Effect of Substituent and Double Benzannulation

“…A similar process allows obtaining boranil derivatives (Figure b). , However, in that event the proton of an OH group is substituted in the last step of the synthetic route leading to a N–B–O type linkage. Yet another class of compounds with BF 2 moiety are diketonates (Figure c) that also constitute an increasingly popular family, − whereas diiminates − (with BF 2 bonded to two nitrogen atoms) (Figure d) as well as ketoiminates − (Figure e) with unsymmetrically bonded BF 2 moiety have also been studied. Globally, the BF 2 -carrying molecules are the most popular organic fluorophores to date and, as Ziessel pointed out, they constitute an “El Dorado for fluorescence tools” .…”

Meta-Alkoxy-Substituted Difluoroboron Dibenzoylmethane Complexes as Environment-Sensitive Materials

“…32 In a computational study, Mirochnik et al used alkoxy donors to change the energy level of the HOMO and nitro-accepting groups to adjust the energy level of the LUMO in BF 2 dbm complexes, where greater red shift in emission resulted from para-substituted nitro acceptors in BF 2 dbm. 33 A decrease in the HOMO−LUMO energy gap with para-substituted accepting groups is also achieved with halide substitution. 34 Typically, para-substituted ketone and ester building blocks are employed in β-diketonate ligand synthesis, which results in π−π* absorption in the corresponding boron dibenzoylmethane dyes.…”

“…Cano et al studied asymmetric alkoxy substitution on both aryl moieties of difluoroboron dibenzoylmethane complexes and found that the asymmetric substitution pattern yielded compounds with larger Stokes shifts and longer emission lifetimes. , Kononevich et al studied alkoxysilyl derivatives of BF 2 dbm and showed that para- and meta-substitution of alkoxysilyl groups resulted in compounds with higher quantum yields and more red-shifted emission compared to ortho -alkoxysilyl substitution . In a computational study, Mirochnik et al used alkoxy donors to change the energy level of the HOMO and nitro-accepting groups to adjust the energy level of the LUMO in BF 2 dbm complexes, where greater red shift in emission resulted from para-substituted nitro acceptors in BF 2 dbm . A decrease in the HOMO–LUMO energy gap with para-substituted accepting groups is also achieved with halide substitution …”