Prompt Fluorescence Research Articles

Luminescence properties of N-isopropylcarbazole single crystal

A systematic study of photoluminescence properties of N-isopropylcarbazole (NIPC) single crystal is reported in this paper. The emission spectra and radiative lifetimes measured within the temperature range 1.7–300 K reveal short- and long-lived luminescence components, the first equivalent to prompt fluorescence (PF) and the second composed of delayed fluorescence (DF) and phosphorescence (PH). Whereas the PF intensity does not show a conclusive temperature dependence, the DF and PH intensities exhibit anomalous temperature dependences involving several distinct maxima. These experimental observations are interpreted in terms of exciton behavior in real organic solids containing exciton traps. It is shown that: (i) PF originates from Frenkel-type excitons (S 1) of energy E S 1 =3.53 eV; (ii) DF is due to emission from the S 1 states produced by triplet-triplet exciton annihilation with E T=3.0 eV; (iii) PHcharacterizes triplet exciton trapping levels with two discrete traps of depths about ϵ (s) t=6×10 -4 eV (shallow trap) and ϵ (d) t=0.3 eV (deep trap). Similar to tetracene single crystals the structural transition in NIPC, known to occur at T t ≅ 140 K, does not show up in the integral emission intensity, indicating its presence by a red shift in the spectra and a weak feature in the monotonic temperature dependence in the singlet exciton lifetime.

Prompt fluorescence from biphenylene in liquid solution: Absence of detectable S 2→S 0 fluorescence and its implications, vibrational structure and polarization of S 1→S 0 fluorescence, and orientational relaxation of molecules in S 1

The prompt emission from S 0→S 2 photoexcited biphenylene in 3-methylpentane has been investigated. No prompt S 2→S 0 fluorescence has been observed. The implications of this negative result are discussed. It is shown that lengthening of the radiative lifetime of S 2 due to intermediate strong S 2-S 1 coupling is the likely cause of the absence of detectable S 2-S 0 fluorescence. The observable resonance Raman lines of biphenylene can be assigned to totally symmetric vibrations. The position of S 1,0 is determined by a vibrational analysis of the S 1→S 0 fluorescence. The polarization degree P of the S 1→S 0 fluorescence is positive. From the dependence of P on temperature and viscosity, orientational relaxation times of biphenylene in S 1 are determined with Perrin's formula.

Changes of Time Courses of Delayed Fluorescence and Prompt Fluorescence during in vivo and in vitro Photoactivation of the Oxygen-evolving System in Dark-grown Spruce Seedlings

Photoactivation of the oxygen-evolving system in intact leaves and in isolated chloroplasts of dark-grown spruce (Picea abies) seedlings was studied by measuring the transient time courses of the delayed and prompt fluorescence of chlorophyll. The delayed fluorescence (measured between 0.5 and 12.5 msec after 15 msec illumination) as well as the prompt fluorescence of intact leaves increased in intensity when the oxygen-evolving system was activated by a short period of illumination. After illumination of chloroplasts isolated from the dark-grown seedlings, the long-lived component of delayed fluorescence (> 100 msec) was enhanced, but not that in the millisecond time range. An analysis of the ionic dependencies of the intensities of prompt and delayed fluorescence showed that the thylakoid membranes of chloroplasts isolated from dark-grown seedlings had almost the same electrostatic properties as those of mature angiosperm chloroplast membranes.

Free-energy change of Photosystem II as measured by delayed luminescence

The intensity of light emission was used to determine the ground-to-excited state free-energy difference of Photosystem II in the alga Scenedesmus quadricauda. Prompt fluorescence measurements give the driving force of that photosystem under illumination while delayed fluorescence indicates the free energy stored in reaction products. Comparison of the light-on and light-off cases suggested that the immediate products were 0.13 eV lower in free energy than the excited state. In the physiological light range, Photosystem II can store 1.0 eV, or about 60% of that needed for photosynthesis, and still shows a ΔG of 0.7 eV after 3 h.

Analysis of the Prompt Fluorescence Induction by Means of Computer Simulation of the Primary Photosynthetic Reactions

Abstract The induction phenomenon of prompt fluorescence of the photosynthetic system in green plants reflects the adaptation of the electron transport system from a dark adapted state to a steady state under light condition. The appearance of the P-peak in the prompt fluorescence induction curve is explained by the decay of the electrochemical gradient across the thylakoid membrane in the dark. The decay of the electrochemical gradient in the dark is calculated using measured fluorescence induction curves with different times of dark adaptation. The influence of photophosphorylation inhibitors is discussed and the threshold effect of ATP-formation depending on the electrochemical gradient is explained by the coupling of the ATP-formation with the electron transport in the thylakoid membrane.

Magnetic field effect on prompt fluorescence in anthracene: evidence for singlet exciton fission

Prompt fluorescence in anthracene is shown to be modified by the application of a magnetic field: characteristic variations of the relative fluorescence quantum yield with field intensity and orientation together with their dependence on the excitation wavelength are reported. The results indicate that the radiationless transitions from the initially excited upper molecular states to the fluorescing levels involve an intermediate singlet state which can dissociate into a triplet pair.