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Volumn 106, Issue 12, 2002, Pages 2935-2944

A time-dependent density functional study of the singlet-triplet energy gap in charge-separated states of rigid bichromophoric molecules

Author keywords

[No Author keywords available]

Indexed keywords

CHARGE-SEPERATED (CS) STATES;

EID: 0037187993     PISSN: 10895639     EISSN: None     Source Type: Journal    
DOI: 10.1021/jp015549e     Document Type: Article
Times cited : (37)

References (91)
  • 1
    • 0001383230 scopus 로고    scopus 로고
    • Balzani, V., Ed.; Wiley-VCH: Weinheim, Germany, Chapter 1
    • Paddon-Row, M.N. In Electron-Transfer In Chemistry; Balzani, V., Ed.; Wiley-VCH: Weinheim, Germany, 2001; Vol. 3, Part 2, Chapter 1, p 179.
    • (2001) Electron-Transfer In Chemistry , vol.3 , Issue.PART 2 , pp. 179
    • Paddon-Row, M.N.1
  • 23
    • 0011147189 scopus 로고    scopus 로고
    • note
    • Within the context of the molecules studied here, the terms CS state and radical ion pair are equivalent.
  • 24
    • 0011109525 scopus 로고    scopus 로고
    • DMN = dimethoxynaphthalene; DCV = dicyanovinyl
    • DMN = dimethoxynaphthalene; DCV = dicyanovinyl.
  • 36
    • 0011121412 scopus 로고    scopus 로고
    • note
    • -1).
  • 47
    • 0011121119 scopus 로고    scopus 로고
    • C7 is defined in Figure 1a
    • C7 is defined in Figure 1a.
  • 49
    • 0011121120 scopus 로고    scopus 로고
    • See Supporting Information
    • See Supporting Information.
  • 50
    • 0011107391 scopus 로고    scopus 로고
    • note
    • This also explains, on electrostatic grounds, why the endo conformation is energetically favored over the exo conformation; electrostatic stabilizing interactions between the oppositely charged chromophores are stronger in the endo conformation, owing to the smaller interchro-mophore separation in this conformation. The fact that electrostatic stabilization is the origin of the energetic preference for the endo conformation was confirmed by calculating the energies of the endo and exo conformations of a model 10-bond DCV radical anion that lacks the DMN radical cation moiety; both endo and exo stereoisomers are now found to be to be essentially isoenergetic.
  • 54
    • 0011080661 scopus 로고    scopus 로고
    • note
    • Correcting the estimated gas-phase CS-state excitation energy of 2.5 eV for DMN[4]DCV for the effect of solvent on the Coulomb electrostatic term and for (Born) solvation energy (see, for example, eq 4a of ref 78) leads to a predicted excitation energy of 1.95 eV in cyclohexane, which is in good accord with the experimental value of 2.10 eV.
  • 56
    • 0011152732 scopus 로고    scopus 로고
    • Personal communication
    • Head-Gordon, M. Personal communication.
    • Head-Gordon, M.1
  • 58
    • 0011088694 scopus 로고    scopus 로고
    • note
    • -, respectively. See Supporting Information.
  • 59
    • 0011119518 scopus 로고    scopus 로고
    • Personal communication
    • Wegner, M. Personal communication.
    • Wegner, M.1
  • 64
    • 0011080662 scopus 로고    scopus 로고
    • note
    • 1A′ symmetry.
  • 65
    • 0011137655 scopus 로고    scopus 로고
    • note
    • 3A″ CS state contains a significant contribution from transitions arising from the local excitation of the DMN chromophore. We point out that, although TD-DFT methods are not CI-based, they do include both dynamic and nondynamic electron correlation and therefore they include the effects covered in the CT interaction mechanism.
  • 66
    • 0011109526 scopus 로고    scopus 로고
    • note
    • ST appears to depend on the relative positioning of the energies of the CS states with respect to the ground and locally excited triplet states of the donor-acceptor pair at its equilibrium geometry.
  • 67
    • 0011083771 scopus 로고    scopus 로고
    • note
    • For example, the computed dipole moment of the locally excited triplet state of DMN[6]DCV is 4 D, compared to 36 D for the corresponding CS state.
  • 68
    • 0011138609 scopus 로고    scopus 로고
    • note
    • 2(1 - 1/ε)(1/R - 1/r), where R is the center-to-center distance between the two charged chromophores, and r is the average radius of the chromophores. For DMN[12]DCV, R = 15.9 Å and r = 4.4 Å. The stabilization energy expression represents the sum of the change in Coulombic interaction upon transfer of the CS state from a vacuum to a solvent, and the (Born) solvation energy of the CS state (see eq 4a of ref 78).
  • 69
    • 0011112609 scopus 로고    scopus 로고
    • note
    • 2 = 0.994 in both cases).
  • 70
    • 0011119042 scopus 로고    scopus 로고
    • note
    • Population analyses reveal that the DCV radical anion is nearly distonic in character, with the radical (unpaired spin density) being localized essentially at C7 and the anionic charge being restricted to the two CN moieties.
  • 73
    • 0011082750 scopus 로고    scopus 로고
    • note
    • ST increases with increasing degree of p ao character in the C7 singly occupied orbital.
  • 76
    • 0011091911 scopus 로고    scopus 로고
    • note
    • The term relaxed geometry is intended to encompass both nuclear and solvent equilibrium configurations.
  • 81
    • 0011084331 scopus 로고    scopus 로고
    • note
    • HT are the electronic coupling elements for electron transfer and hole transfer in the appropriate redox states of the same system; see, for example, ref 79.
  • 82
    • 0011110415 scopus 로고    scopus 로고
    • note
    • In fact, calculations on the 13-bond system, DMN[13]DCV, using pure DFT functionals failed to reach convergence for the two roots corresponding to the triplet and singlet CS states.
  • 83
    • 0011140657 scopus 로고    scopus 로고
    • note
    • ST values is a distinct benefit.
  • 85
    • 0011147890 scopus 로고    scopus 로고
    • note
    • High-level ab initio quantum mechanical methods, such as MR-CI, CAS-PT2, or coupled cluster equations-of-motion, should give more accurate excitation energies than the TD-DFT methods. However, their routine use is currently not feasible for molecules containing more than 20 heavy atoms. Moreover, although these calculations should give good gas-phase singlet-triplet energy gaps, their agreement with solution-phase data is expected to be poor, unless solvation effects are explicitly included in the calculations. This would further increase the numerical intensity of the calculations. It is possible that a semiempirical SCF MO procedure, such as CNDO/S and ZINDO, with explicit inclusion of solvation effects, might give reasonable singlet-triplet energy gaps. This possibility has not yet been explored.


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.