A Coupled-Cluster Analysis of the Electronic Excited States in Aminobenzonitriles

Abstract

The excited states of 4-(N,N-dimethylamino)benzonitrile (DMABN) and 4-aminobenzonitrile (ABN) are characterized by the similarity transformed equation-of-motion coupled-cluster method with single and double excitations (STEOM-CCSD). The long wavelength band of DMABN is assigned by STEOM-CCSD to an emission of a geometrically relaxed twisted intramolecular charge transfer (TICT) state. In contrast, no lowering in total energy upon twisting is found in ABN. The different behavior of the TICT states in ABN and DMABN can quite clearly be understood from the behavior upon twisting of the correlated ionization potentials and electron affinities from IP/EA-EOM-CCSD results that are obtained as a side product of STEOM-CCSD calculations. Inclusion of electron correlation is found to be crucial however, as the effect is largely lost at the Hartree-Fock (Koopmans') level of accuracy. The STEOM-CCSD results are similar to results from DFT/SCI calculations. In general they also agree well with results from previous CASPT2 calculations and experimental data, where available. The crucial behavior of the energy of the TICT states upon rotation of the amino group in ABN and DMABN differs markedly however, between STEOM-CCSD and CASPT2. Whereas in STEOM-CCSD upon twisting we find the expected lowering for the TICT state in DMABN and rise in energy for ABN, this is not the case in CASPT2. Previous benchmarks indicate that CASPT2 may have difficulties describing differential dynamical correlation associated with transitions from lone pair orbitals, and we think therefore that the results at the STEOM-CCSD and DFT/SCI levels may be more accurate for this aspect of the problem.

Microhydrated aromatic cluster cations: Binding motifs of 4-aminobenzonitrile-(H2O)n cluster cations with n ≤ 4

“…32 Thus, the amino group becomes planar upon ionization, and the N-H bonds are calculated to slightly elongate from 1.0056 to 1.0115 Å. 15 The symmetric and antisymmetric N-H stretch fundamentals predicted at ν s NH = 3380 cm −1 and ν a NH = 3492 cm −1 are in good agreement with the measured values of 3390 and 3482 cm −1 , 15, 33 respectively.…”

Aqueous Solvation of p-Aminobenzonitrile in the Excited States: A Molecular Level Theory on Density Dependence

“…6.04, 5.76, and 12.14 D were respectively obtained for the three states by CASSCF wave function (see Table 2). Borst et al reported 6 6.19 6.06 12.25 CASSCF Parusel et al 8 6.81 7.61 11.61 STEOM Borst et al 9 6.41 7.20 a -377.599556 au. b -377.601692 au.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12] Osawa et al recently reported Raman spectra of the CtN stretching vibration of ABN and its electronic absorption spectra in water, methanol, and cyclohexane under sub-and supercritical conditions as well as in acetonitrile under subcritical condition. 12 As the solvent density increases from the gaseous region to F r ) 1.5, where F r is the reduced density by the critical density of the solvent, the absorption peak positions in water and methanol decrease.…”

4‐Aminobenzonitrile: ab initio calculations, FTIR and Raman spectra

“…4ABN is known to be a push-pull molecule, with electron acceptor and donor substituents in para position on the aromatic benzene. Over the past few decades, many experimental 31 -37 and quantum chemical theoretical 38 studies, including the excited states of these molecules, 39,40 have been conducted on 4ABN.…”