What is Fluorescence?

A type of electronic spectroscopy, that is, it involves excitation of electrons—energy absorption to an excited state— followed by emission of a smaller energy as radiation. Fluorescence and Phosphorescence are two types of Luminescence.

What is Fluorescence? Link to Simulation spectrometer: S refers to ‘singlet’ and T to ‘triplet’ states. The S 0 state is the ground state and the subscript numbers, S 1 and S 2, identify individual excited states.

What is Fluorescence? Xe lamp Sample cell photodetector Emission monochromator excitation monochromator

Why is Fluorescence useful in DNA (and other biochemical) Studies? -Fluorescence generally is much more sensitive to the environment of the chromophore than is light absorption. - Fluorescence is a useful technique for following the binding of ligands or conformational changes. - The sensitivity of fluorescence is a consequence of the relatively long time a molecule stays in an excited singlet state before de-excitation. -Absorption is a process that is over in sec, a time scale where the molecule and its environment are effectively static. -In Fluorescence, during the to sec that a singlet remains excited, all kinds of processes can occur, including protonation or deprotonation reactions, solvent-cage relaxation, local conformational changes, and any processes coupled to translational or rotational motion.

What is the connection between Fluorescence and DNA Photocleavage? Ru(bpy) 2 (L) 2+ Ground state {Ru(bpy) 2 (L) 2+ }* Excited state Ru(bpy) 2 (L) 2+ Ground state {Ru(bpy) 2 (L) 2+ }* Excited state + h

What is the connection between Fluorescence and DNA Photocleavage? Ru(bpy) 2 (L) 2+ Ground state {Ru(bpy) 2 (L) 2+ }* Excited state MLCT, d e-   * orbital 1 O 2 singlet state, S 3 O 2 triplet state, T “Ru(bpy) 2 (L) 2+ “ Relaxed state O=O “triplet energy transfer"

What is the connection between Fluorescence and DNA Photocleavage? Ru(bpy) 2 (L) 2+ Ground state {Ru(bpy) 2 (L) 2+ }* 3O23O2 “Ru(bpy) 2 (L) 2+ “ Relaxed state 1O21O2 + h AT TA CG GC AT CG AT TA CoxG GC AT CG

What is the connection between Fluorescence and DNA Photocleavage? Oxidized Guanine bases 3O23O2 1O21O2 AT TA CG GC AT CG AT TA CoxG GC AT CG