Ab Initio Study of Circular Dichroism and Circularly Polarized Luminescence of Spin-Allowed and Spin-Forbidden Transitions: From Organic Ketones to Lanthanide Complexes

Abstract

Complete and restricted active space self-consistent field (CAS-/ RAS-SCF) wavefunction methods are applied for the calculation of circular dichroism (CD) and circularly polarized luminescence (CPL) of a series of molecules comprising four organic ketones, the chiral Cobalt(III) complex Λ-[Co(en) 3 ] 3+ and the Europium(III) complex [Eu(DPA) 3 ] 3 -. The abinitio results are in good agreement with the experimental data and previous results obtained with Kohn-Sham density functional theory in the case of the spin-allowed transitions. CD and CPL properties are calculated ab-initio for the first time for the spin-forbidden transitions of both a transition metal and a lanthanide complex. on a large set of organic compounds and on the spin-allowed transitions of some transition metal complexes. For instance, the experimental CD and CPL spectra of -camphorquinone and ( , )trans--hydrindanone were nicely reproduced when using TDDFT calculations with inclusion of the vibronic effects. 36 The results revealed that in both cases, the chiroptical properties arise from transitions between the and * orbitals of the carbonyl groups. Subsequently, Pecul and Ruud 37 applied TDDFT to a set of bicyclic ketones 38 and showed that the differences in sign and magnitude between abs and lum are essentially related to the structural differences between the ground and excited states. Based on a similar set of compounds, it was shown that equation-of-motion CCSD (EOM-CCSD) and TDDFT with the CAM-B3LYP functional provided similar accuracy for abs and lum , 39 while the popular B3LYP functional led to incorrect results in some of the emission properties.There is also a substantial body of research on the calculation of spin-allowed electronic CD spectra of transition metal complexes, where TDDFT remains the main computational tool. See, e.g., References 33, 40 and 41 for reviews and References 19, 42-50 for selected original studies. CPL calculations for transition metal complexes are scarce in comparison. A first attempt was made in 2008 by Coughlin et al. 21 with the use of TDDFT in combination with an approximate formulation of lum , in order to determine the chiroptical properties associated to the 0 ← 1 emission in a series of Iridium(III) complexes. Another attempt was made in 2013 with the use of multi-reference perturbative methods (CASSCF and CASPT2) on a cycloplatinated-[6]helicene compound. 19 Despite the ability of lanthanide complexes to exhibit the largest dissymmetry factors, no ab-initio calculations of CD or CPL properties have been performed yet. Theoretical work on lanthanide complexes has so far relied on CF models 51,52 in combination with the semiempirical Judd-Ofelt theory. 53,54 Recently, such CF based models were used to simulate the CD spectrum 55 and the Raman optical activity 56 of Ln-based compounds. TDDFT has been also used to calculate the CD spectrum of some Eu(III) and Yb(III) complexes, [57][58][59] but these studies focused on the UV-Vis part of the energy spectrum which corresponds mostly to intra-ligand ...

Beyond Chiral Organic (p-Block) Chromophores for Circularly Polarized Luminescence: The Success of d-Block and f-Block Chiral Complexes

“…Any contribution arising from the coupling between the electric dipole (ED) and electric quadrupole (EQ) moments is neglected in the rotatory strength equation since the consideration of an isotropic medium implies the orientation average (Gendron et al, 2019). The comparison of CPL intensities of different compounds showing different quantum yields requires some normalization of the rotatory strength by the global emission contribution which is ruled by the dipole strength (D ij ) depicted in Equation ( 3), where − → Q ij is the electric transition quadrupole moment (Gendron et al, 2019).…”

“…Despite the many examples reported to date, the relationship between the structure of the complex and the value of g lum , which is of fundamental importance for molecular programming, remains challenging. This weakness mainly relies on the difficulties of performing theoretical CPL studies accessible to synthetic coordination chemists (Gendron et al, 2019). The potential applications of CPL arising from chiral Ln 3+ systems is of considerable importance in biology and biochemistry because they have shown to be very sensitive to small changes in the molecular structure which can be detected as a change in the CPL emission.…”

Luminescence, Chiroptical, Magnetic and Ab-Initio Crystal-Field Characterizations of an Enantiopure Helicoidal Yb(III) Complex: The Van Vleck Rennaissance

“…Such a procedure was successfully applied recently to obtained the CPL spectrum of an analogous Eu(III) tris-dipicolinate complex. 33 At 0 K, the calculated CPL spectrum exhibits a strong positive and a strong negative band corresponding to the 0' → 0 and 0' → 1 transitions, respectively. The increase of the temperature leads to the appearance of a second positive band corresponding to the 1' → 0 transition, as observed experimentally.…”

Yellow Circularly Polarized Luminescence from C1‐Symmetrical Copper(I) Complexes

“…The probability of emitting a circularly polarized photon is proportional to the rotatory strength of the transition. According to Gendron et al., a non‐negligible spin‐orbit coupling (SOC) results in the spin angular momentum component of the rotatory strength becoming non‐null. Additionally, SOC can intensify the orbital angular momentum component in the magnetic transition dipole.…”