Photoinduced Charge-Separation and Charge-Recombination Processes of Fullerene[60] Dyads Covalently Connected with Phenothiazine and Its Trimer

Abstract

Photoinduced charge-separation and charge-recombination processes of fullerene[60] dyads covalently connected with phenothiazine and its trimer (PTZ n -C 60, n = 1 and 3) with a short amide linkage were investigated. A time-resolved fluorescence study provided evidence of charge separation via the excited singlet state of a C 60 moiety ( (1)C 60*), which displayed high efficiencies in various solvents; Phi (S) CS (quantum yield of charge separation via (1)C 60*) = 0.59 (toluene) to 0.87 (DMF) for PTZ 1-C 60 and 0.78 (toluene) to 0.91 (DMF) for PTZ 3-C 60. The transient absorption measurement with a 6 ns time resolution in the visible and near-IR regions showed evidence of the generation of radical ion pairs in relatively polar solvents for both dyads. In nonpolar toluene, only PTZ 1- (3)C 60* was observed for PTZ 1-C 60, whereas PTZ 3- (3)C 60* as well as the radical ion pair state in equilibrium were observed for PTZ 3-C 60. The radical ion pairs had relatively long lifetimes: 60 (DMF) to 910 ns ( o-dichlorobenzene) for (PTZ) 1 (*+)-C 60 (*-) and 230 (PhCN) to 380 ns ( o-dichlorobenzene) for (PTZ) 3 (*+)-C 60 (*-). The small reorganization energy (lambda) and the electronic coupling element (| V|) were estimated by the temperature dependence of the charge-recombination rates, i.e., lambda = 0.53 eV and | V| = 1.6 cm (-1) for (PTZ) 3 (*+)-C 60 (*-).

Reverse phenomena of magnetic field effects and time-resolved EPR spectra in the photogenerated biradical from intramolecular electron-transfer in a phenothiazine–C60linked compound with a semi-rigid spacer

“…In the case of Ph(BP)C 60 and Ph(n)C 60 (n = 612), the MFEs in lower magnetic fields (< 0.2 T) are explained by both of isotropic hfc and SLR mechanismsas reported previously[9][10][11][12][13][14]. The isotropic hfc mechanism can be discussed by a semitheoretical value (B 1/2 ) of the half width of the MFEs, where B 1/2 is given by B 1/(B 1 + B 2 ), and B 1 and B 2 refer to the hyperfine interaction between the nuclear spins and unpaired electron spins in each radical[4]. The hfc constant of the C 60 moiety with a substituent was neglected since the C 60 moiety component of B 1/2value is evaluated to be below 0.1 mT[19].…”

“…There has been considerable interest in photoinduced electron-transfer reactions in donor (D)-C 60 systems [1][2][3]. C 60 has been used in solar energy conversion systems such as dye-sensitized solar cells [4] and organic thin-film solar cells [5]. For further applications, a deeper understanding of the photoinduced electron-transfer reactions using C 60 is required.…”

Functionalized Nanocarbons for Artificial Photosynthesis: From Fullerene to SWCNT, Carbon Nanohorn, and Graphene

“…The structure of C 60 -PTZ is shown in Fig. 6a [ 17 ], in which C 60 and PTZ moieties are separated with several single bonds, suggesting absence of direct π-interactions.…”

“…On the basis of the MO energy diagram, visible-light excitation of the central SubPc induces CS process from SubPc* to C 60 , which corresponds to an electron transfer from the LUMO+1 of SubPc to the LUMO of C 60 , generating PTZ 3 -SubPc •− at 1,020 nm. Reconstructed using data from reference [ 17 ] three PTZs as seen from the HOMO in Fig. 8a .…”

Preservation of the donor–acceptor character of a carbazole–phenalenone dyad upon adsorption on Pt(111)

“…2 Donor-acceptor dyads enable intramolecular electron transfer induced by thermal, electrical or optical stimulation and oen show uorescence or solvatochromism. [3][4][5][6][7] However, the application of donor-acceptor dyads in advanced devices requires a careful molecular design regarding the efficiency of electron transfer and the lifetime of the charge separated state. Several factors have been suggested to enhance the quantum yields and lifetimes in the charge separated states, such as spin restriction rules, conformational gating, and orientation effects.…”