Low-lying excited states and nonradiative processes of the adenine analogues 7H- and 9H-2-aminopurine

Simon Lobsiger, Rajeev K. Sinha, Maria Trachsel, Samuel Leutwyler

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Abstract

We have investigated the UV vibronic spectra and excited-state nonradiative processes of the 7H- and 9H-tautomers of jet-cooled 2-aminopurine (2AP) and of the 9H-2AP-d4 and -d5 isotopomers, using two-color resonant two-photon ionization spectroscopy at 0.3 and 0.045 cm-1 resolution. The S1 S0 transition of 7H-2AP was observed for the first time. It lies ∼ 1600 cm-1 below that of 9H-2AP, is ∼1000 times weaker and exhibits only in-plane vibronic excitations. In contrast, the S1 S0 spectra of 9H-2AP, 9H-2AP-d 4, and 9H-2AP-d5 show numerous low-frequency bands that can be systematically assigned to overtone and combinations of the out-of-plane vibrations 1′, 2′, and 3′. The intensity of these out-of-plane bands reflects an out-of-plane deformation in the 1(La) state. Approximate second-order coupled-cluster theory also predicts that 2-aminopurine undergoes a butterfly deformation in its lowest 1 state. The rotational contours of the 9H-2AP, 9H-2AP-d4, and 9H-2AP-d5 000 bands and of eight vibronic bands of 9H-2AP up to 000+600 cm-1 exhibit 75-80 in-plane (ab) polarization, which is characteristic for a 1 excitation. A 20-25 c-axis (perpendicular) transition dipole moment component may indicate coupling of the 1 bright state to the close-lying 1n dark state. However, no 1n vibronic bands were detected below or up to 500 cm-1 above the 1 000 band. Following 1 excitation, 9H-2AP undergoes a rapid nonradiative transition to a lower-lying long-lived state with a lifetime 5s. The ionization potential of 9H-2AP was measured via the 1 state (IP = 8.020 eV) and the long-lived state (IP > 9.10 eV). The difference shows that the long-lived state lies 1.08 eV below the 1 state. Time-dependent B3LYP calculations predict the 3 (T1) state 1.12 eV below the 1 state, but place the 1n (S1) state close to the 1 state, implying that the long-lived state is the lowest triplet (T1) and not the 1n state.

Original languageEnglish
Article number114307
JournalJournal of Chemical Physics
Volume134
Issue number11
DOIs
Publication statusPublished - 21-03-2011

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2-Aminopurine
adenines
Adenine
Excited states
analogs
excitation
tautomers
ionization potentials
dipole moments
low frequencies
harmonics
color
ionization
life (durability)
vibration
photons
polarization
spectroscopy
Ionization potential
Dipole moment

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

Cite this

@article{5c56c6b1ff8742729d8f906cc8108e68,
title = "Low-lying excited states and nonradiative processes of the adenine analogues 7H- and 9H-2-aminopurine",
abstract = "We have investigated the UV vibronic spectra and excited-state nonradiative processes of the 7H- and 9H-tautomers of jet-cooled 2-aminopurine (2AP) and of the 9H-2AP-d4 and -d5 isotopomers, using two-color resonant two-photon ionization spectroscopy at 0.3 and 0.045 cm-1 resolution. The S1 S0 transition of 7H-2AP was observed for the first time. It lies ∼ 1600 cm-1 below that of 9H-2AP, is ∼1000 times weaker and exhibits only in-plane vibronic excitations. In contrast, the S1 S0 spectra of 9H-2AP, 9H-2AP-d 4, and 9H-2AP-d5 show numerous low-frequency bands that can be systematically assigned to overtone and combinations of the out-of-plane vibrations 1′, 2′, and 3′. The intensity of these out-of-plane bands reflects an out-of-plane deformation in the 1(La) state. Approximate second-order coupled-cluster theory also predicts that 2-aminopurine undergoes a butterfly deformation in its lowest 1 state. The rotational contours of the 9H-2AP, 9H-2AP-d4, and 9H-2AP-d5 000 bands and of eight vibronic bands of 9H-2AP up to 000+600 cm-1 exhibit 75-80 in-plane (ab) polarization, which is characteristic for a 1 excitation. A 20-25 c-axis (perpendicular) transition dipole moment component may indicate coupling of the 1 bright state to the close-lying 1n dark state. However, no 1n vibronic bands were detected below or up to 500 cm-1 above the 1 000 band. Following 1 excitation, 9H-2AP undergoes a rapid nonradiative transition to a lower-lying long-lived state with a lifetime 5s. The ionization potential of 9H-2AP was measured via the 1 state (IP = 8.020 eV) and the long-lived state (IP > 9.10 eV). The difference shows that the long-lived state lies 1.08 eV below the 1 state. Time-dependent B3LYP calculations predict the 3 (T1) state 1.12 eV below the 1 state, but place the 1n (S1) state close to the 1 state, implying that the long-lived state is the lowest triplet (T1) and not the 1n state.",
author = "Simon Lobsiger and Sinha, {Rajeev K.} and Maria Trachsel and Samuel Leutwyler",
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Low-lying excited states and nonradiative processes of the adenine analogues 7H- and 9H-2-aminopurine. / Lobsiger, Simon; Sinha, Rajeev K.; Trachsel, Maria; Leutwyler, Samuel.

In: Journal of Chemical Physics, Vol. 134, No. 11, 114307, 21.03.2011.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Low-lying excited states and nonradiative processes of the adenine analogues 7H- and 9H-2-aminopurine

AU - Lobsiger, Simon

AU - Sinha, Rajeev K.

AU - Trachsel, Maria

AU - Leutwyler, Samuel

PY - 2011/3/21

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N2 - We have investigated the UV vibronic spectra and excited-state nonradiative processes of the 7H- and 9H-tautomers of jet-cooled 2-aminopurine (2AP) and of the 9H-2AP-d4 and -d5 isotopomers, using two-color resonant two-photon ionization spectroscopy at 0.3 and 0.045 cm-1 resolution. The S1 S0 transition of 7H-2AP was observed for the first time. It lies ∼ 1600 cm-1 below that of 9H-2AP, is ∼1000 times weaker and exhibits only in-plane vibronic excitations. In contrast, the S1 S0 spectra of 9H-2AP, 9H-2AP-d 4, and 9H-2AP-d5 show numerous low-frequency bands that can be systematically assigned to overtone and combinations of the out-of-plane vibrations 1′, 2′, and 3′. The intensity of these out-of-plane bands reflects an out-of-plane deformation in the 1(La) state. Approximate second-order coupled-cluster theory also predicts that 2-aminopurine undergoes a butterfly deformation in its lowest 1 state. The rotational contours of the 9H-2AP, 9H-2AP-d4, and 9H-2AP-d5 000 bands and of eight vibronic bands of 9H-2AP up to 000+600 cm-1 exhibit 75-80 in-plane (ab) polarization, which is characteristic for a 1 excitation. A 20-25 c-axis (perpendicular) transition dipole moment component may indicate coupling of the 1 bright state to the close-lying 1n dark state. However, no 1n vibronic bands were detected below or up to 500 cm-1 above the 1 000 band. Following 1 excitation, 9H-2AP undergoes a rapid nonradiative transition to a lower-lying long-lived state with a lifetime 5s. The ionization potential of 9H-2AP was measured via the 1 state (IP = 8.020 eV) and the long-lived state (IP > 9.10 eV). The difference shows that the long-lived state lies 1.08 eV below the 1 state. Time-dependent B3LYP calculations predict the 3 (T1) state 1.12 eV below the 1 state, but place the 1n (S1) state close to the 1 state, implying that the long-lived state is the lowest triplet (T1) and not the 1n state.

AB - We have investigated the UV vibronic spectra and excited-state nonradiative processes of the 7H- and 9H-tautomers of jet-cooled 2-aminopurine (2AP) and of the 9H-2AP-d4 and -d5 isotopomers, using two-color resonant two-photon ionization spectroscopy at 0.3 and 0.045 cm-1 resolution. The S1 S0 transition of 7H-2AP was observed for the first time. It lies ∼ 1600 cm-1 below that of 9H-2AP, is ∼1000 times weaker and exhibits only in-plane vibronic excitations. In contrast, the S1 S0 spectra of 9H-2AP, 9H-2AP-d 4, and 9H-2AP-d5 show numerous low-frequency bands that can be systematically assigned to overtone and combinations of the out-of-plane vibrations 1′, 2′, and 3′. The intensity of these out-of-plane bands reflects an out-of-plane deformation in the 1(La) state. Approximate second-order coupled-cluster theory also predicts that 2-aminopurine undergoes a butterfly deformation in its lowest 1 state. The rotational contours of the 9H-2AP, 9H-2AP-d4, and 9H-2AP-d5 000 bands and of eight vibronic bands of 9H-2AP up to 000+600 cm-1 exhibit 75-80 in-plane (ab) polarization, which is characteristic for a 1 excitation. A 20-25 c-axis (perpendicular) transition dipole moment component may indicate coupling of the 1 bright state to the close-lying 1n dark state. However, no 1n vibronic bands were detected below or up to 500 cm-1 above the 1 000 band. Following 1 excitation, 9H-2AP undergoes a rapid nonradiative transition to a lower-lying long-lived state with a lifetime 5s. The ionization potential of 9H-2AP was measured via the 1 state (IP = 8.020 eV) and the long-lived state (IP > 9.10 eV). The difference shows that the long-lived state lies 1.08 eV below the 1 state. Time-dependent B3LYP calculations predict the 3 (T1) state 1.12 eV below the 1 state, but place the 1n (S1) state close to the 1 state, implying that the long-lived state is the lowest triplet (T1) and not the 1n state.

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