Revealing the electronic properties of the B–B bond: the bis-catecholato diboron molecule

Abstract

The electronic properties of a diboron molecule, namely the Bis(cathecolato)diboron (2-(1,3,2-benzodioxaborol-2-yl)-1,3,2-benzodioxaborole), (B2Cat2) have been studied by comparing photoemission (XPS) and Near Edge absorption spectroscopy (NEXAFS) experiments with the outcome of...

Accurate Vertical Excitation Energies of BODIPY/Aza-BODIPY Derivatives from Excited-State Mean-Field Calculations

“…To bypass this problem, Boulanger et al proposed a protocol where vertical excitation energies were calculated with the Bethe–Salpeter formalism or with the scaled opposite spin (SOS) CIS­(D) method, which adds a perturbative correction for double excitations on top of a CIS calculation . Actually the importance of double excitations for the description of low-lying excited states is not restricted to BODIPYs and related families, , but it appears to be related to the presence of boron in the molecular skeleton and has been recently evidenced in a series of works focused on near-edge X-ray absorption of boroxine-containing compounds. − In particular, it was shown in refs and that while transition-state (TS) and TDDFT methods with a selection of xc potentials ranging from GGA to global, meta-separated, and range-separated hybrids fail to account for the correct intensity distribution of the lowest two spectral features, assigned to π* valence core excited states, a qualitatively correct description was obtained with a computationally inexpensive ΔSCF procedure . This observation, together with a recent publication by Worster et al, which showed that ΔSCF is able to predict excitation energies with an accuracy competitive with and sometimes better than that of TDDFT, prompted us to benchmark ΔSCF against TDDFT on a series of 17 BODIPYs and aza-BODIPYs considered by Momeni and Brown and Feldt and Brown (see Figure ) in the quest for an accurate yet efficient mean-field method that could be used for a fast screening of candidate dyes for a specific application.…”

“… 34 − 37 In particular, it was shown in refs ( 35 and 36 ) that while transition-state (TS) and TDDFT methods with a selection of xc potentials ranging from GGA to global, meta-separated, and range-separated hybrids fail to account for the correct intensity distribution of the lowest two spectral features, assigned to π* valence core excited states, a qualitatively correct description was obtained with a computationally inexpensive ΔSCF procedure. 35 This observation, together with a recent publication by Worster et al, 38 which showed that ΔSCF is able to predict excitation energies with an accuracy competitive with and sometimes better than that of TDDFT, prompted us to benchmark ΔSCF against TDDFT on a series of 17 BODIPYs and aza-BODIPYs considered by Momeni and Brown 39 and Feldt and Brown 40 (see Figure 2 ) in the quest for an accurate yet efficient mean-field method that could be used for a fast screening of candidate dyes for a specific application. In this work, the accuracy of the ΔSCF method is explored and contrasted with that of TDDFT for a quite extensive range of xc potentials.…”

Computational NEXAFS Characterization of Molecular Model Systems for 2D Boroxine Frameworks

“…Considering, in particular, the B K-edge spectrum, significant spectral differences emerged with respect to the NEXAFS spectra of the phenylcontaining boroxine monolayer [6], which clearly indicate the different chemistry of boron in the two systems. More importantly, the B1s spectrum of the boroxine framework differs from that of the bis-catecholato diboron molecule (B 2 Cat 2 ) on Au(111) [14], where two resonances are visible in the p-polarization. These features were identified as π(B-B) bonding and antibonding transitions through DFT calculations, and considered as a probe of the B-B bond formation on the surface.…”

“…At the DFT-TP level, the main relaxation effects following the core-hole formation [15,16] are included and good results are generally expected for K-shell excitations of light atoms in the periodic table. The theoretical description of B1s' core excitations in boronic systems is, however, challenging, as the static correlation effects have to be included in the computational approach, as demonstrated in our previous works [14,17]. Static and dynamic correlation effects can be described by using wave-function-based approaches [17], which are, however, limited to rather small systems.…”

“…Static and dynamic correlation effects can be described by using wave-function-based approaches [17], which are, however, limited to rather small systems. The computationally cheaper ∆SCF-DFT (∆SCF) method has been demonstrated to be effective for describing the B1s' core excited states of the diboron system B 2 Cat 2 [14]. At the ∆SCF level, the relaxation changes among different excited-state configurations relative to the same core-hole are taken into account at variance with the DFT-TP approach, which includes the relaxation in an average way.…”