Temperature dependence of the rates of photophysical processes of fluorenone
01 Jan 1988-The Journal of Physical Chemistry (American Chemical Society)-Vol. 92, Iss: 13, pp 3842-3845
TL;DR: In this article, the rate coefficients for the dominant photophysical processes depopulating the fluorescent state have been found to depend on the solvent and temperature, and the solvent dependence is attributed to the different extent of energy shift for the various excited states involved in these processes.
Abstract: Fluorescence lifetimes, fluorescence quantum yields, and triplet yields have been measured as a function of temperature in
five solvents of different polarity. The rate coefficients for the dominant photophysical processes depopulating the fluorescent
state have been found to depend on the solvent and temperature. The solvent dependence is attributed to the different extent
of energy shift for the various excited states involved in these processes. The experimental results require the assumption
of temperature-dependent and -independent singlet-triplet intersystem crossing rates. The temperature-dependent process
is identified as a thermoneutral or endothermic transition from the lowest excited singlet to a higher triplet state.
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TL;DR: A series of statistical copolymers of 9,9-dihexylfluorene and 9-fluorenone with well-defined structures were synthesized and used to investigate the photophysics, origin of the green emission, and electroluminescence of this class of light-emitting materials as discussed by the authors.
Abstract: A series of four new statistical copolymers of 9,9-dihexylfluorene and 9-fluorenone with well-defined structures and a new fluorene−fluorenone−fluorene trimer model compound were synthesized and used to investigate the photophysics, origin of the green emission, and electroluminescence of this class of light-emitting materials. We show that the new oligofluorene trimer with a central fluorenone moiety is an excellent model of the green-emitting chromophore in polyfluorenes. From systematic studies of the steady-state photoluminescence (PL) and PL decay dynamics of solutions of the fluorenone-containing copolymers and oligomer and thin films of the copolymers, we show that the controversial 535-nm green emission band originates from the fluorenone defects in single-chain polyfluorenes and not from intermolecular aggregates or excimers. The green emission, centered at 535 nm, was observed in dilute toluene solutions of all fluorenone-containing copolymers and oligomer; it was long-lived with a single-expone...
209 citations
TL;DR: In this article, the photophysical properties of the N-H and N-methyl derivatives of 1,2-, 2,3- and 1,8-naphthalimides have been studied.
Abstract: The photophysical properties of the N—H and N-methyl derivatives of 1,2-, 2,3- and 1,8-naphthalimides have been studied. The shift of the fluorescence emission position as a function of the solvent polarity indicates only a weak variation of dipole moment for the excited state compared with the corresponding value in the ground state (5.7 D for 2b, 2.8 D for 3b and <2 D for 4b, 1 D ≈ 3.335 64 × 10–30 C m, and 2b, 3b and 4b are N-methyl-1,2- naphthalimide, N-methyl-2,3-napthalimide and N-methyl-1,8-naphthalimide). However, important modifications of the photophysical properties are observed which depend on the relative position of the dicarboximide moiety on the naphthalene ring: the intersystem crossing rate constant of 4b increases dramatically by three orders of magnitude compared with that of 2b; simultaneously, the fluorescence quantum yield decreases from 0.77 to 0.03, although the corresponding rate constant, kf, increases. This difference is found to arise from the energy gap between the lowest1(π, π*) singlet excited state and the upper 3(n,π*) triplet state, which is of the order of 9 kcal mol–1 for 2b and less than 2 kcal mol–1 for 4b in acetonitrile solution. Protic solvents increase the energy difference between the n,π* and π,π* states thus decreasing the mixing of the two levels; as a consequence, the lifetime of 4b is increased, i.e. from <60 ps in hexane to 2.1 ns in trifluoroethanol. A triplet–triplet annihilation process occurs with the N-methyl derivatives 3b and 4b which leads to a monomer delayed fluorescence with the former, and mainly to a delayed excimer emission with the latter.
199 citations
TL;DR: In this paper, the authors studied the kinetics of dynamic quenching of singlet and triplet fluorenone by a series of alcohols, phenols, and related compounds, in which hydrogen-bonding power, redox potential, and acidity are systematically varied.
Abstract: In order to clarify mechanisms of excited state interactions in hydrogen-bonded pairs, we have studied the kinetics of dynamic quenching of singlet and triplet fluorenone by a series of alcohols, phenols, and related compounds, in which hydrogen-bonding power, redox potential, and acidity are systematically varied. In addition, effects of solvent basicity or polarity and deuteration help identify the role of hydrogen-bonding in physical or chemical quenching processes. Alcohols and weak acids, with high oxidation potentials, do not quench the triplet, but quench the singlet at rates which parallel hydrogen-bonding power. This is attributed to a physical mechanism, involving vibronic coupling to the ground state via the hydrogen bond. This is much stronger in the excited state than in the ground state, and provides efficient energy dissipation in the radiationless transition. Phenols, with hydrogen-bonding power comparable to that of the alcohols but with much lower oxidation potentials, quench both single...
162 citations
TL;DR: In this article, the effects of substituents on the N-phenyl group on solvent polarity and viscosity have been studied, and a short-wavelength (SW) fluorescence, similar to the luminescence emitted by the n-alkyl derivatives, and/or a considerably red shifted long-wvelength (LW) luminecence are observed, and the ratio of the SW and LW fluorescence components is found to depend on substitution and on solvent properties.
Abstract: Absorption and fluorescence spectra, fluorescence decay times, and quantum yields of fluorescence and triplet state formation have been determined for N-phenyl and substituted N-phenyl derivatives of 1,2-, 2,3-, and 1,8-naphthalimides, using stationary irradiation and laser flash excitation methods. The effects of substituents on the N-phenyl group on solvent polarity and viscosity have been studied. A short-wavelength (SW) fluorescence, similar to the luminescence emitted by the N-alkyl derivatives, and/or a considerably red shifted long-wavelength (LW) luminescence are observed, and the ratio of the SW and LW fluorescence components is found to depend on substitution and on solvent properties. A striking characteristic of the N-phenylnaphthalimides (in contrast to the N-alkyl derivatives) is the very efficient internal conversion which results in short fluorescence decay times and in low fluorescence and triplet yields. On the basis of the experimental results, it is suggested that solvent and geometric...
124 citations
TL;DR: Studies of the photophysical properties of OFnK in solution and thin film by steady-state and time-resolved fluorescence spectroscopic measurements suggest efficient funneling of excitation energy from the photoexcited fluorene segments to the low-energy fluorenone sites by both intra- and intermolecular hopping events whereby they give rise to green emission.
Abstract: Oligofluorenes (a trimer, pentamer, and heptamer) with one fluorenone unit in the center (OFnK: n=3, 5, or 7) were synthesized and used as models to understand the origin of the low-energy emission band in the photoluminescence and electroluminescence spectra of some polyfluorenes. All compounds form glasses with T(g) at 30 degrees C (OF3 K), 50 degrees C (OF5 K) and 57 degrees C (OF7 K). Oligomers OF5 K and OF7 K exhibit smectic liquid crystal phases that undergo transition to isotropic melts at 107 and 205 degrees C, respectively. Oligomer OF5 K could be obtained in form of single crystals. The X-ray structure analysis revealed the helical nature of the molecule and a helix reversal defect located at the central fluorenone unit. The packing pattern precludes formation of excimers. Electrochemical properties were investigated by cyclic voltammetry. The ionization potential (I(p)) and electron affinity (E(a)) were calculated from these data. Studies of the photophysical properties of OFnK in solution and thin film by steady-state and time-resolved fluorescence spectroscopic measurements suggest efficient funneling of excitation energy from the photoexcited fluorene segments to the low-energy fluorenone sites by both intra- and intermolecular hopping events whereby they give rise to green emission. Intermolecular energy transfer was investigated by using a model system composed of a highly defect free polyfluorene PF2/6 doped by OFnK. Forster-type energy transfer takes place from PF2/6 to OFnK. The energy-transfer efficiency increases predictably with increasing concentration of OFnK.
101 citations