Transient Raman studies on the structure of the chloranil-alkylbenzene triplet charge-transfer complexes

Abstract

Transient resonance Raman spectroscopy has been used to study the structure of chloranilalkylbenzene triplet chargetransfer complexes in solution. Resonance excitation conditions were chosen so that only Raman bands due to chloranil vibrations were selectively enhanced. The Raman spectra of the complexes with weak donors were similar to that of TI chloranil, while those of the complexes with strong donors were similar to that of the chloranil anion radical. The observed vibrational frequencies of chloranil in the triplet complexes were plotted as a function of the ionization potential of donors, and common "S-shape (or inverted S-shape)" dependence was observed for all the vibrations. This S-shape dependence was well-reproduced by a simple theory. It was concluded that the molecular structure of the chloranil moiety in these triplet complexes is intermediate between that of the free TI state and that of the anion radical. The structure changes in accordance with the change in the electron-donating ability of donors, reflecting the change in the magnitude of the charge transfer occurring in the complexes.

Electron injection dynamics in dye-sensitized semiconductor nanocrystalline films

“…Therefore, [D * A] ex shows absorption bands similar to those of D * [locally excited (LE) state] and the CT band in transient absorption spectroscopy [122,[124][125][126]. On the other hand, when D þ A -is energetically more stable than D * A, an exciplex composed of an ion pair, [D þ A -] ex (δΦ N þ Φ I ), is formed and shows absorption bands similar to those of D þ and A -, together with the CT band where an optical transition from [D þ A -] ex to [D * A] ex occurs [122,[124][125][126][127]. Here, we call the exciplex having a neutral character 'neutral exciplex' and that composed of an ion pair 'ionic exciplex'.…”

“…where V is the electronic coupling matrix element by the CT interaction [125,126]. The optical transition for E CT corresponds to a CT transition (neutral-to-ionic transition for the neutral exciplex), and it appears often in the near-IR region.…”

Investigations of bimolecular photoinduced electron transfer reactions in polar solvents using ultrafast spectroscopy

“…ion pairs and exciplexes is still unknown. Time-resolved vibrational spectroscopy, which has been very scarcely used in this field [119][120][121][122], should give a new insight. Time-resolved multidimensional IR spectroscopy, which is just emerging [123,124], might prove to be a powerful tool to investigate the geometry of these bimolecular complexes.…”

Time‐resolved study of the photochemical reaction of 4‐dimethylaminobenzonitrile with carbon tetrachloride

“…3 -5,37 -40 Besides the ¾1020 cm 1 band which becomes active only at later times, all the other observed bands have their counterparts in the resonance Raman spectra of ground-state and radical cation DMABN. 30 Referring to the vibrational assignments of benzene derivatives containing chlorine atom(s) 38 and related compounds such as chloranil, 53 the 1020 cm 1 band is tentatively assigned to C ring -Cl stretching C C ring -C ring stretching vibration. Although its assignment to the in-plane C-H bending vibration Wilson 18a 34,36,37 cannot be ruled out, this possibility seems unlikely considering the very small changes seen in the other pure C-H in-plane bending vibration (Wilson 9a at ¾1170 cm 1 ) during the 13 ps growth time of the ¾1020 cm 1 band.…”