TY - JOUR
T1 - High-Energy Long-Lived Mixed Frenkel-Charge-Transfer Excitons
T2 - From Double Stranded (AT)n to Natural DNA
AU - Vayá, Ignacio
AU - Brazard, Johanna
AU - Huix-Rotllant, Miquel
AU - Thazhathveetil, Arun K.
AU - Lewis, Frederick D.
AU - Gustavsson, Thomas
AU - Burghardt, Irene
AU - Improta, Roberto
AU - Markovitsi, Dimitra
N1 - Funding Information:
Financial support from the French Agency for Research (ANR- 10-BLAN-0809-01 and ANR -12-BS08-0001-01), JCI-2011-09926, and PCIG12-GA-2012-334257 (grant to I.V.), a postdoctoral fellowship of the Alexander von Humboldt foundation (grant to M.H.R.), the CNRS-CNR PICS project (N86827-2015) and the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division under award DE-FG02-96ER14604 (F.D.L.) is acknowledged. D.M. thanks Ms Marion Perron for sample preparation.
Publisher Copyright:
© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
PY - 2016/3/24
Y1 - 2016/3/24
N2 - The electronic excited states populated upon absorption of UV photons by DNA are extensively studied in relation to the UV-induced damage to the genetic code. Here, we report a new unexpected relaxation pathway in adenine-thymine double-stranded structures (AT)n. Fluorescence measurements on (AT)n hairpins (six and ten base pairs) and duplexes (20 and 2000 base pairs) reveal the existence of an emission band peaking at approximately 320 nm and decaying on the nanosecond time scale. Time-dependent (TD)-DFT calculations, performed for two base pairs and exploring various relaxation pathways, allow the assignment of this emission band to excited states resulting from mixing between Frenkel excitons and adenine-to-thymine charge-transfer states. Emission from such high-energy long-lived mixed (HELM) states is in agreement with their fluorescence anisotropy (0.03), which is lower than that expected for π-π∗ states (≥0.1). An increase in the size of the system quenches π-π∗ fluorescence while enhancing HELM fluorescence. The latter process varies linearly with the hypochromism of the absorption spectra, both depending on the coupling between π-π∗ and charge-transfer states. Subsequently, we identify the common features between the HELM states of (AT)n structures with those reported previously for alternating (GC)n: High emission energy, low fluorescence anisotropy, nanosecond lifetimes, and sensitivity to conformational disorder. These features are also detected for calf thymus DNA in which HELM states could evolve toward reactive π-π∗ states, giving rise to delayed fluorescence. High-energy long-lived mixed (HELM) excitons are populated during excited-state relaxation in (AT)n duplexes. They result from mixing between Frenkel excitons and adenine-to-thymine charge-transfer states and extend over at least four bases on both strands. The properties of HELM states (high emission energy, low fluorescence anisotropy, nanosecond lifetime, and sensitivity to conformational disorder) are also detected for natural DNA.
AB - The electronic excited states populated upon absorption of UV photons by DNA are extensively studied in relation to the UV-induced damage to the genetic code. Here, we report a new unexpected relaxation pathway in adenine-thymine double-stranded structures (AT)n. Fluorescence measurements on (AT)n hairpins (six and ten base pairs) and duplexes (20 and 2000 base pairs) reveal the existence of an emission band peaking at approximately 320 nm and decaying on the nanosecond time scale. Time-dependent (TD)-DFT calculations, performed for two base pairs and exploring various relaxation pathways, allow the assignment of this emission band to excited states resulting from mixing between Frenkel excitons and adenine-to-thymine charge-transfer states. Emission from such high-energy long-lived mixed (HELM) states is in agreement with their fluorescence anisotropy (0.03), which is lower than that expected for π-π∗ states (≥0.1). An increase in the size of the system quenches π-π∗ fluorescence while enhancing HELM fluorescence. The latter process varies linearly with the hypochromism of the absorption spectra, both depending on the coupling between π-π∗ and charge-transfer states. Subsequently, we identify the common features between the HELM states of (AT)n structures with those reported previously for alternating (GC)n: High emission energy, low fluorescence anisotropy, nanosecond lifetimes, and sensitivity to conformational disorder. These features are also detected for calf thymus DNA in which HELM states could evolve toward reactive π-π∗ states, giving rise to delayed fluorescence. High-energy long-lived mixed (HELM) excitons are populated during excited-state relaxation in (AT)n duplexes. They result from mixing between Frenkel excitons and adenine-to-thymine charge-transfer states and extend over at least four bases on both strands. The properties of HELM states (high emission energy, low fluorescence anisotropy, nanosecond lifetime, and sensitivity to conformational disorder) are also detected for natural DNA.
KW - DNA
KW - excitons
KW - fluorescence spectroscopy
KW - hypochromism
KW - quantum chemistry
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U2 - 10.1002/chem.201504007
DO - 10.1002/chem.201504007
M3 - Article
C2 - 26928984
AN - SCOPUS:84961730181
VL - 22
SP - 4904
EP - 4914
JO - Chemistry - A European Journal
JF - Chemistry - A European Journal
SN - 0947-6539
IS - 14
ER -