Electron Energy Loss and DFT/SCI Study of the Singlet and Triplet Excited States of Aminobenzonitriles and Benzoquinuclidines:  Role of the Amino Group Twist Angle

Abstract

Spectroscopic consequences of varying the twist angle of the amino group in aminobenzonitrile systems in the electronic ground state are investigated by applying electron energy loss (EEL) spectroscopy and density functional theory to 4-N,N-dimethylaminobenzonitrile (DMABN), 4-N,N-dimethylamino-3,5-dimethylbenzonitrile (MMD), benzoquinuclidine (BQ), and 6-cyanobenzoquinuclidine (CBQ). A number of singlet and triplet excited states was observed and assigned with the help of DFT/SCI theory. The results characterize the gas-phase spectroscopy of the molecules and verify to within 0.3 eV the predictive power of DFT/SCI theory for vertical states over a wide range of twist and pyramidalization angles. The amino group configuration in the relaxed charge-transfer state of dual fluorescent aminobenzonitriles in solution cannot be directly deduced from the present data, however.

Intramolecular Charge Transfer with N,N-Dialkyl-4-(Trifluoromethyl)anilines and 4-(Dimethylamino)benzonitrile in Polar Solvents. Investigation of the Excitation Wavelength Dependence of the Reaction Pathway

“…Due to the larger dipole moment of the S 2 state [17][18][19], the S 1 band more and more disappears with increasing solvent polarity under the S 2 absorption, as seen for DEE (Fig. 1b) and MeCN (Fig.…”

“…In the last solvent of high polarity, there is no longer a sign of the S 1 band in the absorption spectrum of DMABN. This means that the energy gap ∆E(S 1 , S 2 ) of DMABN decreases when the solvent polarity becomes larger (Table I) [17,18]. As emphasized in the PICT model [4,5,8,9], this decrease in ∆E(S 1 , S 2 ) leads to the appearance of an ICT fluorescence band to the red of the LE emission.…”

“…1. For DMABN in n-hexane, the weak and structured S 1 band is clearly visible at the low-energy side of the main, more strongly allowed, S 2 absorption [17,18]. Whereas the S 0 → S 1 transition corresponds to the weak S 0 → 1 L b absorption of benzene, the S 2 state has an important charge transfer (CT) admixture to the 1 L a state of benzene origin [19].…”

“…It was assumed that the S 2 state is predominantly prepared during the excitation process, due to the substantially larger transition dipole moment of S 0 → S 2 as compared with S 0 → S 1 [17][18][19]. The possibility to excite the D/A molecule exclusively into S 1 , precluding access to the S 2 /S 1 CI, was not explicitly taken into account.…”

A theoretical forecast of the hydrogen bond changes in the electronic excited state for BN and its derivatives

“…BN and some of its derivatives have received great attention as ideal probes of the local environment. The hydrogen-bonding interactions between the nitrile groups and the protic solvents are of considerable interest since the vibration of the nitrile group is basically decoupled from the other part of the molecule and is sensitive to the formation of the hydrogen bond [51][52][53][54][55][56][57][58]. The CN vibration of BN affected by the hydrogen bonding environments was investigated by Aschaffenburg et al [59].…”