Photophysical processes in fluorenone
01 Oct 1978-The Journal of Physical Chemistry (American Chemical Society)-Vol. 82, Iss: 21, pp 2304-2309
TL;DR: In this paper, the flash transient spectrum is given over a wide spectral range in acetonitrile and hydrocarbon solvents, and is assigned to the triplet on the basis of both its decay kinetics and accompanying delayed emission.
Abstract: Flash-photolytic measurements of photophysical parameters of fluorenone are presented. The flash transient spectrum is given over a wide spectral range in acetonitrile and hydrocarbon solvents, and is assigned to the triplet on the basis of both its decay kinetics and accompanying delayed emission. This corresponds spectrally to prompt fluorescence and is accurately second order in transient concentration. Relative triplet quantum yields (phi/sub T/) are obtained from the dependence of the transient absorption on flash energy. Measurements of florescence lifetimes, quantum yields, and phi/sub T/'s give rate constants for all degradative processes of the lowest excited singlet. In acetonitrile the rates of intersystem crossing and internal conversion to the ground state from the lowest excited singlet are comparable. The absence of phosphorescence and the measured triplet lifetime (approximately 2 ms) in rigid media at 77K give a lower limit for the radiative lifetime (tau/sub o/ > 0.2s) which is compatible with a ..pi..-..pi..* assignment for the lowest triplet.
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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 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: The extinction coefficient of triplet benzophenone in benzene has been directly determined by absolute measurements of absorbed energy and triplet absorbance, deltaD/sup 0//sub T/, under demonstrably linear conditions where incident excitation energy, E/sub 0/, and ground state absorbance (A/Sub 0)/ are both extrapolated to zero as discussed by the authors.
Abstract: The extinction coefficient epsilon/sub T/, of triplet benzophenone in benzene has been directly determined by absolute measurements of absorbed energy and triplet absorbance, deltaD/sup 0//sub T/, under demonstrably linear conditions where incident excitation energy, E/sub 0/, and ground state absorbance, A/sub 0/, are both extrapolated to zero The result, 7220 +- 320 M/sup -1/ cm/sup -1/ at 530 nm, validates and corrects many measurements of triplet and radical extinctions and yields, using the energy-transfer method As E/sub 0/ and A/sub 0/ both decrease, deltaD/sup 0//sub T/ becomes proportional to their product In this situation, the ratio R = (1/A/sub 0/) (ddeltaD/sup 0//sub T//dE/sub 0/) = (epsilon/sub T/ /sup -/ epsilon/sub G/)phi/sub T/ Measurements of R, referred to benzophenone, give (epsilon/sub T/ - epsilon/sub G/)phi/sub T/ for any substance, without necessity for absolute energy calibration Both absolute and relative laser flash measurements on zinc tetraphenyl porphyrin (epsilon/sub T/ - epsilon/sub G/ at 470 nm = 73 x 10/sup 4/ M/sup -1/ cm/sup -1/) give phi/sub T/ = 083 +- 004 6 figures, 2 tables
159 citations
TL;DR: In this paper, the extinction coefficients of the triplet state of C60 were obtained by energy-transfer techniques in flash photolysis studies, and the values permit actinometric measurement of triplet quantum yield (φR=0.93±0.07).
131 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