TY - JOUR

T1 - A Computational Approach to Nontraditional Intrinsic Luminescence

T2 - Vibrationally Resolved Absorption and Fluorescence Spectra of DABCO

AU - Rožić, Tomislav

AU - Hochlaf, Majdi

AU - Ben Said, Ridha

AU - Došlić, Nada

N1 - Funding Information: This research has been supported by the Humboldt Foundation Linkage Programme and the Croatian Science Foundation under Grant HRZZ IP-2016-06-1142. Calculations were performed using the resources of the computer cluster Isabella of the University of Zagreb University Computing Centre (SRCE). We would like to thank COST Action CA18212 - Molecular Dynamics in the GAS phase (MD-GAS) supported by COST (European Cooperation in Science and Technology). We thank W. Domcke (Munich) and G. Solomon (Copenhagen) for reading the manuscript and for insightful comments. Publisher Copyright: © 2022 American Chemical Society. All rights reserved.

PY - 2022

Y1 - 2022

N2 - Recently, so-called "nontraditional intrinsic luminescence" has been reported in several macromolecular systems. Although DABCO (1,4-diazabicyclo[2.2.2]octane) is the first system in which the effect was observed, a thorough analysis of the optical properties of the molecule, which would reveal the origin of this mysterious effect, is still pending. We perform an advanced post-Hartree-Fock treatment of the low-lying electronic states of this molecule, which need to be described with care because of their pronounced Rydberg character. We take a deeper look into the low-lying electronic transitions of DABCO targeting the explanation of the complex vibronic structures of its absorption and fluorescence spectra. Two electronic states, the 1E′(n+3pxy) and 1A2″(n+3pz) states, contribute to the absorption spectrum in the 39000-46000 cm-1spectral range. We also reveal the spectroscopic signature of the 1A2″(n+3pz) state. The analyses of the contributions of individual vibrational normal modes allowed the identification of those giving rise to the complex vibronic structures of the spectra. Fluorescence emission arises from the vibronic coupling of the one-photon forbidden transition between the 1A1′(n+3s) state and the electronic ground state. The spectrum, which can be interpreted in terms of populating a few vibrational normal modes, is shifted toward visible wavelengths mostly due to the forced interaction of the lone pair electrons of the two nitrogen atoms. Our work on DABCO may help to rationalize the luminescence of more complex systems containing tertiary amine groups.

AB - Recently, so-called "nontraditional intrinsic luminescence" has been reported in several macromolecular systems. Although DABCO (1,4-diazabicyclo[2.2.2]octane) is the first system in which the effect was observed, a thorough analysis of the optical properties of the molecule, which would reveal the origin of this mysterious effect, is still pending. We perform an advanced post-Hartree-Fock treatment of the low-lying electronic states of this molecule, which need to be described with care because of their pronounced Rydberg character. We take a deeper look into the low-lying electronic transitions of DABCO targeting the explanation of the complex vibronic structures of its absorption and fluorescence spectra. Two electronic states, the 1E′(n+3pxy) and 1A2″(n+3pz) states, contribute to the absorption spectrum in the 39000-46000 cm-1spectral range. We also reveal the spectroscopic signature of the 1A2″(n+3pz) state. The analyses of the contributions of individual vibrational normal modes allowed the identification of those giving rise to the complex vibronic structures of the spectra. Fluorescence emission arises from the vibronic coupling of the one-photon forbidden transition between the 1A1′(n+3s) state and the electronic ground state. The spectrum, which can be interpreted in terms of populating a few vibrational normal modes, is shifted toward visible wavelengths mostly due to the forced interaction of the lone pair electrons of the two nitrogen atoms. Our work on DABCO may help to rationalize the luminescence of more complex systems containing tertiary amine groups.

U2 - 10.1021/acs.jpca.1c09256

DO - 10.1021/acs.jpca.1c09256

M3 - Journal article

C2 - 35168330

AN - SCOPUS:85125121105

VL - 126

SP - 1094

EP - 1102

JO - Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory

JF - Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory

SN - 1089-5639

IS - 7

ER -