Kinetic and spectroscopic study of triplet state and ionic pathways in the laser-induced photoexcitation of N-ethylcarbazole in fluid solutions

Triplet Photophysics of Multichromophoric Molecules. A Study of Poly(N-vinylcarbazole) and meso-2,4-Dicarbazolylpentane in Fluid Solutions

“…Furthermore, it appears that triplet states and excited singlet states can be formed by recombination of these ionic species. 5 In addition, both excimeric delayed fluorescence (EDF) and excimeric phosphorescence were found in high dielectric solvents such as ethanol, but only monomeric emissions were found in low dielectric solvents such as cyclohexane. Again these assignments were made in accord with earlier observations of these excimeric species.6•7 If we use 2Cz+ and 2Cz~to symbolize the carbazolyl radical cation and anion, respectively, the formation of these species by laser photoexcitation may be represented by a multiphoton process, 1Cz0 + X^{2Cz+...2X"} (1) where lCzo is a ground-state NEC molecule, 2X" may be either 2Cz_ or a solvent anion, with the bracketed species representing a geminate ion pair.…”

“…If these two Cz groups happened to be oppositely charged, fast intramolecular ion recombination could very well lead to singlet excimer formation. Another exception could be realized if the back electron transfer produced a triplet state instead of an excited singlet directly 2Cz+ + 2Cz" -3Cz* + ^Zq (5) or indirectly 2Cz+ + 2Cz™ -^z* + ^Zq -3Cz* + ^Zq (6) In this case some tens of microseconds are available for the conversion 3Cz* + ^Zq -3D* (7) to occur before the triplet state is lost by relaxation or quenching. In fact, it has been found in earlier work1 that excimeric phosphorescence is produced upon UV laser excitation of NEC even in high-viscosity glycerol solutions, thus indicating the viability of this mechanism.…”

Intramolecular Triplet Energy Transfer. 4. A Carbazole−Naphthalene System Having a Flexible Alkyl Spacer Doped in Poly(methyl methacrylate) Matrixes

“…Figure shows transient absorp- tion spectra of EtCz and Cz− n −Np ( n = 4−8) in PMMA matrix at room temperature with a delay time of 72 ns. The top spectrum was attributed to 3 Cz*, whereas the bottom spectrum was attributed to the Np triplet state produced by the energy transfer from Cz. It is clear that the triplet energy of Cz is being transferred to Np, and the transfer rate can be observed by monitoring the 500-nm absorbance; at 500 nm, only the 3 Cz* absorbance is present in this particular experiment.…”

An Investigation of Triplet States, Radical Ions, and Triplet Excimers Produced by Laser Photoexcitation of Phenyldibenzophosphole in Fluid Solutions and Rigid Media

“…In solvents of low dielectric constant, ion recombination is relatively fast and excited singlet states are the primary products. In solvents of high dielectric constant, recombination is relatively slower and the net yield of triplet states is larger because their probability of formation by the ion route is enhanced and because they are also formed in intersystem The reversibility arrows in eq 4 are used advisedly since the singlettriplet energy gap for PDP is only 2100 cm"1, smaller than that of eosin which is the classical prototype for E-type delayed fluorescence.42 If the transient triplet population were sufficiently large, then T-T annihilation could compete with the reverse of eq 4 to produce delayed fluorescence, Tm + Tm-1S*+1S0 (5) It is likely that this is occurring in DMF at delay times less than 1 ms where the triplet population is relatively large and the solvent is sufficiently fluid so that a diffusion-controlled reaction, such as eq 5, can occur with sufficient speed. In the mixed solvent, EtOH/glycerol, the transient triplet population is also expected to be relatively large, but in this case solvent viscosity works against eq 5 and the E-type production of delayed fluorescence is favored.…”