Photobiophisik I Flashcards
Was ist das Lambert Beersche Gesetzt?
- Wie lautet die Formel?
- was kann damit gemessen werden?
relates the attenuation of light to the properties of the material through which the light is travelling bzw. Die Abnahme der Lichtintensität ( Io/I in Photonen/cm^2) ist proportional der Teilchenanzahl der absorbierenden Molekülen.
A: Absorption –> wie wiel Licht geht durch die Küvette/A= log (Io/I)
Epsilon: Molaren Absorptionskoeffizient
c: Konzentration
s or d: Küvettenlänge
Beschriben Sie die Formel von der Lambert-Beersches Gesetz für makroskopischen Messungen
Io/I = 10^E2-10^E1
T: Transmission –> Anteil des Lichts, der durch die Küvette geht.
Was ist Fluoreszenz & wie funktioniert ihre Mechanismus?
Fluorescence occurs when an excited molecule, atom, or nanostructure, relaxes to a lower energy state (possibly the ground state) through emission of a photon.
–> relaxation from the S1 to So.
–> The Photon maintains the Energy as:
E =hv (v-frequency, h-Plack´s constant)
What is phosphorescence?
Phosphorescence describes the process by which the electron which absorbed the photonundergoes intersystem crossing into an energy state of different spin multiplicity-a triplet state. As a result, the excited electron can become trapped in the triplet state with only “forbidden” transitions available to return to the lower energy singlet state. The relaxation, thus
Was ist die Fluoreszenz Lebensdauer?
…
What is the quantum yield bzw. Quantumausbeute?
The fluorescence quantum yield gives the efficiency of the fluorescence process. It is defined as the ratio of the number of photons emitted to the number of photons absorbed.
–> max: 1 bzw. 100%
Explain the Born-Oppenheimer approximation and its relation to the Franck-Condon principle.
it is the assumption that the motion of atomic nuclei and electrons in a molecule can be treated separately, based on the fact that the nuclei are much heavier than the electrons.
—> As a Lösungsmethode der Schrödinger-Gleichung
= der angeregte Elektron landet in S1-Zustand unter Beibehaltung der Kernkoordinaten, die sich erst später ändern.
Frank-Condon Principle
- that explains the intensity of vibronic transitions. Vibronic transitions are the simultaneous changes in electronic and vibrational energy levels of a molecule due to the absorption or emission of a photon of the appropriate energy. The principle states that during an electronic transition, a change from one vibrational energy level to another will be more likely to happen if the two vibrational wave functions overlap more significantly.
Was ist den Franck-Condon Bereich?
the Franck–Condon principle is the approximation that an electronic transition is most likely to occur without changes in the positions of the nuclei in the molecular entity and its environment.
The resulting state is called a Franck–Condon state, and the transition involved, a vertical transition.
In the quantum mechanical picture, the vibrational levels and vibrational wavefunctions are those of quantum harmonic oscillators –> Oscillator model
Was ist den Stoke´s Shift?
Stokes shift is the difference (in energy, wavenumber or frequency units) between positions of the band maxima of the absorption and emission spectra of the same electronic transition.
When a systemabsorbs a photon, it gains energy and enters an excited state. One way for the system to relax is to emit a photon, thus losing its energy (another method would be the loss of energy as heat). When the emitted photon has less energy than the absorbed photon, this energy difference is the Stokes shift.
–> VIBRATIONAL RELAXATION
–> die Abstrahlung Wellenlänge ist GRÖßER- also weniger Energie, als die absorbierte Strahlung.
Erlautern Sie welche Formen von strahlende Desaktivierung es gibt und woran unterscheiden sie sich untereinander?
- FLUORESZENZ
- Spontan emittierte Strahlung klingt sofort wieder ab, wenn die anregende Strahlung abgeschaltet ist.
- S1 –>So
- PHOSPHORESZENZ
- ISC–> Triplett Zustand, also ungepparten Elektronen mit paralellen Spin
- T1 –> So
Beschreiben Sie alle Prozessen des Jablonski Diagramms.
So= Groundstate
S1= excited state
T1= triplett state –> ungepaarten Spin,
IC = internal conversion –>is a radioactive decay process wherein an excited nucleus interacts electromagnetically with one of the orbital electrons of the atom. This causes the electron to be emitted (ejected) from the atom.
ISC= intersystem crossing –> radiationless process involving a transition between the two electronic states with different states spin multiplicity.
Vibrational relaxation –> relaxation of an excited-vibrational state molecule to less energetic vibrational modes through the transfer of vibrational energy (heat). Importantly, there is no change in electronic state.
Fluorescence –> Relaxation through photon emmision / Stokes shift, from S1-So
Phosphorescence –> Relaxation through photon emmision from T1-So
Wie viele Photonen pro Zeit werden von 1 Farbmolekül emittiert?
Was ist Photobleaching? Beschreiben sie dieses Prozess.
Bleaching limits the observation time of a fluorophore. It is a complex chemical process which may be:
oxygen-dependent intensity-dependent reversible
Was ist Polarisation bei fluorescent dyes?
Was ist GFP?
The green fluorescent protein (GFP) is a protein composed of 238 amino acid residues (26.9 kDa) that exhibits bright green fluorescence when exposed to light in the blue to ultraviolet range.
from the jellyfish Aequoria victoria. The cloning of the cDNA opened the possibility of using GFP as a label for a variety of genetically cellular proteins. This particularly showed that fusion frequently to the C-terminal or the N-terminal of various proteins has no effect on the function of the protein.
Was ist FRET?
- is a mechanism describing energy transfer between two light-sensitive molecules (chromophores).
- A donor chromophore, initially in its electronic excited state, may transfer energy to an acceptor chromophore through nonradiative dipole–dipole coupling.
- The efficiency of this energy transfer is inversely proportional to the sixth power of the distance between donor and acceptor, making FRET extremely sensitive to small changes in distance.
- Measurements of FRET efficiency can be used to determine if two fluorophores are within a certain distance of each other.
Wie funktionieren ratiometrische Farben? und geben Sie ein Beispiel davon.
- A ratio between two fluorescence intensity is calculated in ratiometric measurements: this is performed using ion indicators that, on binding calcium, present an emission spectral shift or excitation spectral shift. Compounds which have a shift in their spectra on binding to ions are commonly referred as ratiometric indicators.
- FURA-2 and Ca2+
