Dual fluorescence and ultrafast intramolecular charge transfer with 6- N, N-dialkylaminopurines. A two-state model

A. Demeter, Sergey I. Druzhinin, Sergey A. Kovalenko, Tamara A. Senyushkina, Klaas A. Zachariasse

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

6-N,N-Dimethyl-9-methyladenine (DMPURM) and 6-N,N-dimethyladenine (DMPURH) show dual fluorescence from a locally excited (LE) and an intramolecular charge transfer (ICT) state in solvents of different polarity over extended temperature ranges. The fluorescence quantum yields are very small, in particular those of LE. For DMPURM in acetonitrile (MeCN) at 25 °C, for example, Φ′(ICT) = 3.2 × 10-3 and Φ(LE) = 1.6 × 10-4. The large value of Φ′(ICT)/Φ(LE) indicates that the forward LE → ICT reaction is much faster than the back reaction. The data obtained for the intersystem crossing yield Φ(ISC) show that internal conversion (IC) is the dominant deactivation channel from LE directly to the ground state S0. For DMPURM in MeCN with Φ(ISC) = 0.22, Φ(IC) = 1 - Φ(ISC) - Φ′(ICT) - Φ(LE) = 0.78, whereas in cyclohexane an even larger Φ(IC) of 0.97 is found. The dipole moment gradually increases upon excitation, from 2.5 D (S0), via 6 D (LE) to 9 D (ICT) for DMPURM and from 2.3 D (S0), via 7 D (LE) to 8 D (ICT) for DMPURH. From the temperature dependence of Φ′(ICT)/Φ(LE), a reaction enthalpy -ΔH of 11 kJ/mol is obtained for DMPURM in n-hexane (ε25 = 1.88), increasing to 17 kJ/mol in the more polar solvent di-n-butyl ether (ε25 = 3.05). With DMPURM in diethyl ether, an activation energy of 8.3 kJ/mol is determined for the LE → ICT reaction (ka). The femtosecond excited state absorption spectra at 22 °C undergo an ultrafast decay: 1.0 ps in CHX and 0.63 ps in MeCN for DMPURM, still shorter (0.46 ps) for DMPURH in MeCN. With DMPURM in n-hexane, the LE fluorescence decay time τ2 increases upon cooling from 2.6 ps at -45 °C to 6.9 ps at -95 °C. The decay involves ICT and IC as the two main pathways: 1/τ2 ≃ ka + kIC. As a model compound (no ICT) is not available, its lifetime τ0(LE) ∼ 1/kIC is not known, which prevents a separate determination of ka. The excited state reactions of DMPURM and DMPURH are treated with a two-state model: S0 → LE ⇆ ICT. With 6-N-methyl-9-methyladenine (MPURM) and 9-methyladenine (PURM), the fluorescence quantum yield is very low (-5) and dominated by impurities, due to enhanced IC from LE to S0.

Original languageEnglish
Pages (from-to)1521-1537
Number of pages17
JournalJournal of Physical Chemistry A
Volume115
Issue number9
DOIs
Publication statusPublished - Mar 10 2011

Fingerprint

Charge transfer
Fluorescence
charge transfer
fluorescence
internal conversion
Quantum yield
Excited states
Ether
decay
excitation
diethyl ether
Dipole moment
cyclohexane
deactivation
Ground state
acetonitrile
Absorption spectra
Enthalpy
ethers
polarity

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Dual fluorescence and ultrafast intramolecular charge transfer with 6- N, N-dialkylaminopurines. A two-state model. / Demeter, A.; Druzhinin, Sergey I.; Kovalenko, Sergey A.; Senyushkina, Tamara A.; Zachariasse, Klaas A.

In: Journal of Physical Chemistry A, Vol. 115, No. 9, 10.03.2011, p. 1521-1537.

Research output: Contribution to journalArticle

Demeter, A. ; Druzhinin, Sergey I. ; Kovalenko, Sergey A. ; Senyushkina, Tamara A. ; Zachariasse, Klaas A. / Dual fluorescence and ultrafast intramolecular charge transfer with 6- N, N-dialkylaminopurines. A two-state model. In: Journal of Physical Chemistry A. 2011 ; Vol. 115, No. 9. pp. 1521-1537.
@article{e2b65acda36f40969bca492d1ad30245,
title = "Dual fluorescence and ultrafast intramolecular charge transfer with 6- N, N-dialkylaminopurines. A two-state model",
abstract = "6-N,N-Dimethyl-9-methyladenine (DMPURM) and 6-N,N-dimethyladenine (DMPURH) show dual fluorescence from a locally excited (LE) and an intramolecular charge transfer (ICT) state in solvents of different polarity over extended temperature ranges. The fluorescence quantum yields are very small, in particular those of LE. For DMPURM in acetonitrile (MeCN) at 25 °C, for example, Φ′(ICT) = 3.2 × 10-3 and Φ(LE) = 1.6 × 10-4. The large value of Φ′(ICT)/Φ(LE) indicates that the forward LE → ICT reaction is much faster than the back reaction. The data obtained for the intersystem crossing yield Φ(ISC) show that internal conversion (IC) is the dominant deactivation channel from LE directly to the ground state S0. For DMPURM in MeCN with Φ(ISC) = 0.22, Φ(IC) = 1 - Φ(ISC) - Φ′(ICT) - Φ(LE) = 0.78, whereas in cyclohexane an even larger Φ(IC) of 0.97 is found. The dipole moment gradually increases upon excitation, from 2.5 D (S0), via 6 D (LE) to 9 D (ICT) for DMPURM and from 2.3 D (S0), via 7 D (LE) to 8 D (ICT) for DMPURH. From the temperature dependence of Φ′(ICT)/Φ(LE), a reaction enthalpy -ΔH of 11 kJ/mol is obtained for DMPURM in n-hexane (ε25 = 1.88), increasing to 17 kJ/mol in the more polar solvent di-n-butyl ether (ε25 = 3.05). With DMPURM in diethyl ether, an activation energy of 8.3 kJ/mol is determined for the LE → ICT reaction (ka). The femtosecond excited state absorption spectra at 22 °C undergo an ultrafast decay: 1.0 ps in CHX and 0.63 ps in MeCN for DMPURM, still shorter (0.46 ps) for DMPURH in MeCN. With DMPURM in n-hexane, the LE fluorescence decay time τ2 increases upon cooling from 2.6 ps at -45 °C to 6.9 ps at -95 °C. The decay involves ICT and IC as the two main pathways: 1/τ2 ≃ ka + kIC. As a model compound (no ICT) is not available, its lifetime τ0(LE) ∼ 1/kIC is not known, which prevents a separate determination of ka. The excited state reactions of DMPURM and DMPURH are treated with a two-state model: S0 → LE ⇆ ICT. With 6-N-methyl-9-methyladenine (MPURM) and 9-methyladenine (PURM), the fluorescence quantum yield is very low (-5) and dominated by impurities, due to enhanced IC from LE to S0.",
author = "A. Demeter and Druzhinin, {Sergey I.} and Kovalenko, {Sergey A.} and Senyushkina, {Tamara A.} and Zachariasse, {Klaas A.}",
year = "2011",
month = "3",
day = "10",
doi = "10.1021/jp109609f",
language = "English",
volume = "115",
pages = "1521--1537",
journal = "Journal of Physical Chemistry A",
issn = "1089-5639",
publisher = "American Chemical Society",
number = "9",

}

TY - JOUR

T1 - Dual fluorescence and ultrafast intramolecular charge transfer with 6- N, N-dialkylaminopurines. A two-state model

AU - Demeter, A.

AU - Druzhinin, Sergey I.

AU - Kovalenko, Sergey A.

AU - Senyushkina, Tamara A.

AU - Zachariasse, Klaas A.

PY - 2011/3/10

Y1 - 2011/3/10

N2 - 6-N,N-Dimethyl-9-methyladenine (DMPURM) and 6-N,N-dimethyladenine (DMPURH) show dual fluorescence from a locally excited (LE) and an intramolecular charge transfer (ICT) state in solvents of different polarity over extended temperature ranges. The fluorescence quantum yields are very small, in particular those of LE. For DMPURM in acetonitrile (MeCN) at 25 °C, for example, Φ′(ICT) = 3.2 × 10-3 and Φ(LE) = 1.6 × 10-4. The large value of Φ′(ICT)/Φ(LE) indicates that the forward LE → ICT reaction is much faster than the back reaction. The data obtained for the intersystem crossing yield Φ(ISC) show that internal conversion (IC) is the dominant deactivation channel from LE directly to the ground state S0. For DMPURM in MeCN with Φ(ISC) = 0.22, Φ(IC) = 1 - Φ(ISC) - Φ′(ICT) - Φ(LE) = 0.78, whereas in cyclohexane an even larger Φ(IC) of 0.97 is found. The dipole moment gradually increases upon excitation, from 2.5 D (S0), via 6 D (LE) to 9 D (ICT) for DMPURM and from 2.3 D (S0), via 7 D (LE) to 8 D (ICT) for DMPURH. From the temperature dependence of Φ′(ICT)/Φ(LE), a reaction enthalpy -ΔH of 11 kJ/mol is obtained for DMPURM in n-hexane (ε25 = 1.88), increasing to 17 kJ/mol in the more polar solvent di-n-butyl ether (ε25 = 3.05). With DMPURM in diethyl ether, an activation energy of 8.3 kJ/mol is determined for the LE → ICT reaction (ka). The femtosecond excited state absorption spectra at 22 °C undergo an ultrafast decay: 1.0 ps in CHX and 0.63 ps in MeCN for DMPURM, still shorter (0.46 ps) for DMPURH in MeCN. With DMPURM in n-hexane, the LE fluorescence decay time τ2 increases upon cooling from 2.6 ps at -45 °C to 6.9 ps at -95 °C. The decay involves ICT and IC as the two main pathways: 1/τ2 ≃ ka + kIC. As a model compound (no ICT) is not available, its lifetime τ0(LE) ∼ 1/kIC is not known, which prevents a separate determination of ka. The excited state reactions of DMPURM and DMPURH are treated with a two-state model: S0 → LE ⇆ ICT. With 6-N-methyl-9-methyladenine (MPURM) and 9-methyladenine (PURM), the fluorescence quantum yield is very low (-5) and dominated by impurities, due to enhanced IC from LE to S0.

AB - 6-N,N-Dimethyl-9-methyladenine (DMPURM) and 6-N,N-dimethyladenine (DMPURH) show dual fluorescence from a locally excited (LE) and an intramolecular charge transfer (ICT) state in solvents of different polarity over extended temperature ranges. The fluorescence quantum yields are very small, in particular those of LE. For DMPURM in acetonitrile (MeCN) at 25 °C, for example, Φ′(ICT) = 3.2 × 10-3 and Φ(LE) = 1.6 × 10-4. The large value of Φ′(ICT)/Φ(LE) indicates that the forward LE → ICT reaction is much faster than the back reaction. The data obtained for the intersystem crossing yield Φ(ISC) show that internal conversion (IC) is the dominant deactivation channel from LE directly to the ground state S0. For DMPURM in MeCN with Φ(ISC) = 0.22, Φ(IC) = 1 - Φ(ISC) - Φ′(ICT) - Φ(LE) = 0.78, whereas in cyclohexane an even larger Φ(IC) of 0.97 is found. The dipole moment gradually increases upon excitation, from 2.5 D (S0), via 6 D (LE) to 9 D (ICT) for DMPURM and from 2.3 D (S0), via 7 D (LE) to 8 D (ICT) for DMPURH. From the temperature dependence of Φ′(ICT)/Φ(LE), a reaction enthalpy -ΔH of 11 kJ/mol is obtained for DMPURM in n-hexane (ε25 = 1.88), increasing to 17 kJ/mol in the more polar solvent di-n-butyl ether (ε25 = 3.05). With DMPURM in diethyl ether, an activation energy of 8.3 kJ/mol is determined for the LE → ICT reaction (ka). The femtosecond excited state absorption spectra at 22 °C undergo an ultrafast decay: 1.0 ps in CHX and 0.63 ps in MeCN for DMPURM, still shorter (0.46 ps) for DMPURH in MeCN. With DMPURM in n-hexane, the LE fluorescence decay time τ2 increases upon cooling from 2.6 ps at -45 °C to 6.9 ps at -95 °C. The decay involves ICT and IC as the two main pathways: 1/τ2 ≃ ka + kIC. As a model compound (no ICT) is not available, its lifetime τ0(LE) ∼ 1/kIC is not known, which prevents a separate determination of ka. The excited state reactions of DMPURM and DMPURH are treated with a two-state model: S0 → LE ⇆ ICT. With 6-N-methyl-9-methyladenine (MPURM) and 9-methyladenine (PURM), the fluorescence quantum yield is very low (-5) and dominated by impurities, due to enhanced IC from LE to S0.

UR - http://www.scopus.com/inward/record.url?scp=79952276005&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=79952276005&partnerID=8YFLogxK

U2 - 10.1021/jp109609f

DO - 10.1021/jp109609f

M3 - Article

VL - 115

SP - 1521

EP - 1537

JO - Journal of Physical Chemistry A

JF - Journal of Physical Chemistry A

SN - 1089-5639

IS - 9

ER -