Nils Walter: Chem 260

Vision

2

22

8mLhnEn =

ππππ-to-ππππ*

rhodopsin

Nils Walter: Chem 260

FluorescenceJablonski diagram

If collidingmolecules cannotaccept this larger

energy

nsecfsec

Excitedelectronic state

Groundelectronic state

Vibrational states

Vibrational states

Dissipation inenvironment asheat = internal

conversion

Nils Walter: Chem 260

fsec

internalconversion

Fluorescence quenchingM + hνννν1 →→→→ M*

→→→→ M + hνννν2(fluorescence, kf)→→→→ M + heat (internal conversion, ki)

+ Q →→→→ M + Q*→→→→ M + Q + heat (quenching, kQ)

Molecular species(e.g., H2O, I-) with

suitable energygaps can take up

this energy���� quenching

of fluorescence

][1 Qkkk Qif ++=τkf + ki

Nils Walter: Chem 260

Green: Donor fluorophoreRed: Acceptor fluorophore

����

The molecular dynamics of asingle biomolecule can be

observed by modernfluorescence techniques

Fluorescence quenching:An example from actual research

601��

���

�=rRk

DT τRate of energy transfer

60

6

60

RrREET +

=

Efficiency

Nils Walter: Chem 260

Phosphorescence

min, hoursfsec

Triplet→→→→Singlet state transitionis NOT allowed ���� takes long

radiationless

Nils Walter: Chem 260

Lasers: Light Amplification byStimulated Emission of Radiation

Populationinversion

equilibrium population

laser effect

inverted population pumping