Dynamics of charge-transfer excited states relevant to photochemical energy conversion

Technical Report · Tue Jan 01 04:00:00 EST 1991

OSTI ID:5850768

Lim, E C

Photoinduced Charge Transfer (CT) processes in a series of N-R-N systems, where N stands for naphthalene and R is {minus}CH{sub 2}{minus}, {minus}O{minus}, etc., have been studied in solvents of different polarity. In N-CH{sub 2}{minus}N and N-O-N, time-resolved emission spectra show that initial naphthalene-like monomer band undergoes gradual shift and broadening to yield a structured emission at longer wavelength, as the delay after the laser excitation is increased. Further delay leads to mostly structureless band at still longer wavelength, which resembles the bicimer emission in polar solvents. Formation of the precursor state, and hence the CT state, is shown to involve rotation of one electronically excited moiety with respect to the other to form a twisted structure. Studies of the kinetics of these systems under varying experimental conditions show that the twisted intramolecular CT state can be formed on nanosecond time scales by one-photon excitation of one of the chromophores into a singlet state or on microsecond time scales by two-photon excitations of both chromophores into the lowest triplet state. The fluorescence excitation and dispersed fluorescence spectra of the van der Waals complexes of fluorene with durene, 1,2,4,5-tetrafluorobenzene, and 1,2,4,5-tetrachlorobenzene have been studied in supersonic jets. The fluorene/tetrachlorobenzene system, unlike the others, exhibits exciplex formation upon excitation of fluorene to its lowest excited singlet state (S{sub 1}). The stability of the fluorene/tetrachlorobenzene exciplex state is attributed to the small electronic gap between S{sub 1} fluorene and S{sub 1} tetrachlorobenzene, which increases exciton resonance between the component molecules. 6 refs., 1 fig.

• Research Organization: Akron Univ., OH (USA). Dept. of Chemistry
• Sponsoring Organization: DOE; USDOE, Washington, DC (USA)
• DOE Contract Number: FG02-89ER14024
• OSTI ID: 5850768
• Report Number(s): DOE/ER/14024-1; ON: DE91012669
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
140505* -- Solar Energy Conversion-- Photochemical
Photobiological
& Thermochemical Conversion-- (1980-)
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500 -- Photochemistry
AROMATICS
CHARGE EXCHANGE
CHEMICAL REACTIONS
COMPLEXES
CONDENSED AROMATICS
CONVERSION
DIMERS
DOCUMENT TYPES
ELECTRON TRANSFER
EMISSION SPECTRA
EMISSION SPECTROSCOPY
ENERGY CONVERSION
ENERGY LEVELS
EXCITED STATES
EXCITONS
FLUID FLOW
FLUORENE
FLUORESCENCE SPECTROSCOPY
GROUND STATES
HYDROCARBONS
LASER SPECTROSCOPY
MOLECULAR STRUCTURE
NAPHTHALENE
ORGANIC COMPOUNDS
PHOTOCHEMICAL REACTIONS
PROGRESS REPORT
QUASI PARTICLES
SPECTRA
SPECTROSCOPY
SUPERSONIC FLOW