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Femtosecond dynamics on excited-state proton/charge-transfer reaction in 4'-N,N-diethylamino-3-hydroxyflavone. The role of dipolar vectors in constructing a rational mechanism.
J Phys Chem A. 2005 May 05; 109(17):3777-87.JP

Abstract

The excitation behaviors for 4'-N,N-diethylamino-3-hydroxyflavone (Ia) have been investigated via femtosecond fluorescence upconversion approaches to gain detailed insights into the mechanism of the proton/charge-transfer coupling reaction. In polar solvents such as CH2Cl2 and CH3CN, in addition to a slow, solvent-polarity-dependent rate (a few tens of picoseconds(-1)) of excited-state intramolecular proton transfer (ESIPT) reported previously, early femtosecond relaxation dynamics clearly reveal that the proton-transfer tautomer emission consists of a rise component of a few hundred femtoseconds. The temporal spectral evolution at the time domain of zero to a few hundred femtoseconds further resolves two distinct emission bands consisting of a proton-transfer tautomer emission and a time-dependent Stokes shifted emission. The results, in combination with ab initio calculations on the dipolar vectors for normal and tautomer species, lead us to unveil the importance of the relationship of the dipolar vectors among various states, and hence the corresponding solvation energetics in the overall ESIPT reaction. We conclude a similar dipolar character between ground-state normal (N) and excited proton-transfer tautomer (T*) species, whereas due to the excited-state intramolecular charge transfer (ESICT), the normal excited state (N*) possesses a large dipolar change with respect to N and T*. ESIPT is thus energetically favorable at the Franck-Condon excited N*, and its rate is competitive with respect to the solvation relaxation process. After reaching the solvent equilibration, there exists an equilibrium between N* and T* states in, for example, CH3CN. Due to the greatly different equilibrium polarization between N* and T*, both forward and reversed ESIPT dynamics are associated with a solvent-induced barrier. The latter viewpoint of the equilibrium type of ESIPT in Ia is in agreement with the previous reports based on steady-state, picosecond, and femtosecond dynamic approaches.

Authors+Show Affiliations

Department of Chemistry, National Taiwan University, Taipei, Taiwan, ROC. chop@ntu.edu.twNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

16833693

Citation

Chou, Pi-Tai, et al. "Femtosecond Dynamics On Excited-state Proton/charge-transfer Reaction in 4'-N,N-diethylamino-3-hydroxyflavone. the Role of Dipolar Vectors in Constructing a Rational Mechanism." The Journal of Physical Chemistry. A, vol. 109, no. 17, 2005, pp. 3777-87.
Chou PT, Pu SC, Cheng YM, et al. Femtosecond dynamics on excited-state proton/charge-transfer reaction in 4'-N,N-diethylamino-3-hydroxyflavone. The role of dipolar vectors in constructing a rational mechanism. J Phys Chem A. 2005;109(17):3777-87.
Chou, P. T., Pu, S. C., Cheng, Y. M., Yu, W. S., Yu, Y. C., Hung, F. T., & Hu, W. P. (2005). Femtosecond dynamics on excited-state proton/charge-transfer reaction in 4'-N,N-diethylamino-3-hydroxyflavone. The role of dipolar vectors in constructing a rational mechanism. The Journal of Physical Chemistry. A, 109(17), 3777-87.
Chou PT, et al. Femtosecond Dynamics On Excited-state Proton/charge-transfer Reaction in 4'-N,N-diethylamino-3-hydroxyflavone. the Role of Dipolar Vectors in Constructing a Rational Mechanism. J Phys Chem A. 2005 May 5;109(17):3777-87. PubMed PMID: 16833693.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Femtosecond dynamics on excited-state proton/charge-transfer reaction in 4'-N,N-diethylamino-3-hydroxyflavone. The role of dipolar vectors in constructing a rational mechanism. AU - Chou,Pi-Tai, AU - Pu,Shih-Chieh, AU - Cheng,Yi-Ming, AU - Yu,Wei-Shan, AU - Yu,Yueh-Chi, AU - Hung,Fa-Tsai, AU - Hu,Wei-Ping, PY - 2006/7/13/pubmed PY - 2007/7/28/medline PY - 2006/7/13/entrez SP - 3777 EP - 87 JF - The journal of physical chemistry. A JO - J Phys Chem A VL - 109 IS - 17 N2 - The excitation behaviors for 4'-N,N-diethylamino-3-hydroxyflavone (Ia) have been investigated via femtosecond fluorescence upconversion approaches to gain detailed insights into the mechanism of the proton/charge-transfer coupling reaction. In polar solvents such as CH2Cl2 and CH3CN, in addition to a slow, solvent-polarity-dependent rate (a few tens of picoseconds(-1)) of excited-state intramolecular proton transfer (ESIPT) reported previously, early femtosecond relaxation dynamics clearly reveal that the proton-transfer tautomer emission consists of a rise component of a few hundred femtoseconds. The temporal spectral evolution at the time domain of zero to a few hundred femtoseconds further resolves two distinct emission bands consisting of a proton-transfer tautomer emission and a time-dependent Stokes shifted emission. The results, in combination with ab initio calculations on the dipolar vectors for normal and tautomer species, lead us to unveil the importance of the relationship of the dipolar vectors among various states, and hence the corresponding solvation energetics in the overall ESIPT reaction. We conclude a similar dipolar character between ground-state normal (N) and excited proton-transfer tautomer (T*) species, whereas due to the excited-state intramolecular charge transfer (ESICT), the normal excited state (N*) possesses a large dipolar change with respect to N and T*. ESIPT is thus energetically favorable at the Franck-Condon excited N*, and its rate is competitive with respect to the solvation relaxation process. After reaching the solvent equilibration, there exists an equilibrium between N* and T* states in, for example, CH3CN. Due to the greatly different equilibrium polarization between N* and T*, both forward and reversed ESIPT dynamics are associated with a solvent-induced barrier. The latter viewpoint of the equilibrium type of ESIPT in Ia is in agreement with the previous reports based on steady-state, picosecond, and femtosecond dynamic approaches. SN - 1089-5639 UR - https://www.unboundmedicine.com/medline/citation/16833693/Femtosecond_dynamics_on_excited_state_proton/charge_transfer_reaction_in_4'_NN_diethylamino_3_hydroxyflavone__The_role_of_dipolar_vectors_in_constructing_a_rational_mechanism_ L2 - https://doi.org/10.1021/jp044205w DB - PRIME DP - Unbound Medicine ER -