Stabilization of carbazole radical cation formed in poly(N-vinylcarbazole) by charge delocalization

Abstract

The transient absorption spectra (charge-resonance (CR) band) of polyfZV-vinylcarbazole) (PVCz) and the copolymers of -vinylcarbazole (VCz) with methyl methacrylate and vinyl acetate were measured by laser photolysis to investigate the charge delocalization in the polymers. For the copolymers in which the fraction of VCz (/vcz) is less than 0.4, the CR band appeared at ca. 1800 nm. In the case of /vcz > 0.5, the CR band was shifted to longer wavelengths with increasing /vcz and the copolymer with /vcz = 0.83 showed the same transient absorption spectrum as PVCz. By considering the sequential distribution of the copolymers, the charge formed in PVCz was found to be delocalized among more than two chromophores. For the copolymer (/vcz = 0.07) having no neighboring chromophore interaction, the radical-cation transfer to a series of amines was measured to investigate the free energy change (AG) dependence of an electron-transfer rate constant (k"). The result shows that there is a linear relationship between log ke and AG. By using this relationship, the stabilization energy of the carbazole radical cation in PVCz was estimated to be 0.5 ± 0.1 eV. This value is larger than that of the carbazole dimer radical cation, i.e., the stabilization by the charge delocalization among more than two chromophores is stronger than that of the dimer radical cation.

Carborane Photochemistry Triggered by Aryl Substitution: Carborane‐Based Dyads with Phenyl Carbazoles

“…The 830 nm transient can be attributed to the radical cation of the Cz unit (CzC + ), because the radical cations of various carbazole compounds generally show characteristic absorptions at around 800 nm. [12] This assignment was firmly supported by the pulse radiolysis of o-1 in 1-chlorobutane, which showed a transient at 830 nm (see Figure S11 in the Supporting Information). To assign the 415 nm bands, spectroelectrochemical (SEC) measurements were performed for o-1 under constant voltage conditions at À1.8 V, a potential corresponding to the one-electron reduction of o-1.…”

A Desirable Hole‐Conducting Coadsorbent for Highly Efficient Dye‐Sensitized Solar Cells through an Organic Redox Cascade Strategy

“…Though the electrochemical interactions between the NKX2677 and HC-A are energetically unfavorable (see Scheme 1b), this hole-transfer mechanism may strongly depend on the energetic overlap between the oxidized dye and HC-A. [28] The latter absorption could be assigned to HC-A radical cation of the carbazole cation radical species, [29] because it cannot absorb the 504 nm pulse laser directly. On the other hand, the transient absorption spectrum originating from the organic HC-A radical cation around 830 nm could not be observed from the HC-A-based film as depicted in Figure 5.…”

Time-resolved Spectroscopic Study on Photocarrier Generation Process in Layered Organic Photoconductors

“…The absorption of the aggregate ion radicals of some aromatic compounds was reported previously [11,12]. For example, the absorption maxima of characteristic bands of the unrelaxed dimer cations of naphthalene and pyrene are situated at about 2100 and 1600 nm, respectively [11].…”