Photoinduced Energy and Electron Transfer between Ketone Triplets and Organic Dyes

Abstract

Cationic organic dyes (phenosafranine, safranine T (ST + ), thiopyronine, and methylene blue) are efficient quenchers of the triplet states of aromatic ketones. The triplets of benzophenone (BP), xanthone, thioxanthone, benzil, and N-methylacridone are quenched by the dyes via energy transfer, generating triplet excited dyes (typically k q ) 5.5 × 10 9 M -1 s -1 for 3 BP * + ST + in acetonitrile solution). Regarding Michler's ketone, p-(dimethylamino)benzophenone, and 3,6-bis(dimethylamino)thioxanthone, the mechanism of triplet quenching is solvent-dependent. Electron transfer occurs in polar solvents like acetonitrile, and energy transfer is the dominant reaction pathway in less polar solvents, such as dichloromethane. Delayed fluorescence of the dye caused by heterotriplet-triplet annihilation involving ketone and dye was detected upon studying the reaction of the dyes with triplet excited ketones (BP, xanthone, thioxanthone, and benzil). By applying two successive laser pulses (λ ex ) 532 and 308 nm, respectively), the rate constant of the reaction 3 BP * + 3 (ST + ) * was determined: k ht ) 1.1 × 10 10 M -1 s -1 .

Magnetic‐Field Effects in Organic Semiconducting Materials and Devices

“…The light emission from the singlet excitons generated from TTA is named delayed fluorescence. [33][34][35] In addition, the TTA must satisfy both spin momentum and energy conservation requirements. In general, there are two particular processes involved in TTA in organic materials: Figure 3.…”

Laser flash photolysis study of the photochemistry of thioxanthone in organic solvents

“…9,10 TX can easily form free radicals from the triplet excited state which permits its use as photoinitiator for polymerization [11][12][13] and as a photosensitizer. 14 In the presence of tertiary amines, the triplet excited state of TX produces an intermediate exciplex, through the involvement of an initial excited charge transfer complex. The exciplex decay leads to the formation of an ion-radical pair which ultimately can form the radical pair ketyl/alkylamino, as result of the hydrogen transfer from the amine radical cation to the thioxanthone anion radical (Scheme 1).…”

Studies of Triton X-165–β-cyclodextrin interactions using both extrinsic and intrinsic fluorescence

“…Extensive exploitation of phenosafranin (3,7-diamino-5-phenyl phenazinium chloride) (Scheme 1) for various photophysical and photobiological applications has been described elsewhere [41][42][43][44][45][46]. It is red in color with a planar tricyclic phenazinium moiety bearing a positive charge.…”

“…It is red in color with a planar tricyclic phenazinium moiety bearing a positive charge. PSF is a water-soluble dye with a characteristic broad absorption peak in the visible region [42].…”