lecture 1 - craggs Flashcards
what where the two noble prizes in 2008 and 2014 for
creation and development green fluorescent protein
development of super-resolved fluorescent microscopy
what does GFP allow you to do
genetically tag a protein of interest and track it in a cell
what is flourescence
a type of luminescence where emission is at longer wavelength than excitation
pros of fluorescence
very sensitive
background
single molecule detection possible
how fast is absorption
1 fs
how fast is flourescence
1 - 10 ns
what environmental factors influence speed of fluorescence
protonation
conformational motion
rotation
quenching
parts of fluorescence spectrometer
excitation source wavelength selection (excitation filter) sample wavelength selection (emission filter) detector
who invented vibronic transitions
aleksander jablonski
the different levels of vibronic transition
ground state - S0
first excited singlet state - S1
second excited singlet state - S2
first excited triplet state - T1
what is intersystem crossing
moves from S1 to T1
electrons with anti-parallel spin which adds to 0
time scale of phosphoresence
1 micro second to minutes
equation of spin multiplicity
2S + 1
S = sum of all electron spins
two possible spins of electrons
+ or - 1/2
why do vibronic transitions occur
instead of excited molecules moving to different atomic coordinates they only have time for vertical transitions
define vibrational relaxation
energy transferred non-radiatively e.g. to solvent due to direct interactions
within S1
what is internal conversion and timescale
from S2 to S1 and 10^-12 seconds same as vibrational relaxation
what is stokes shift
emission longer wavelength
due to energy losses from internal conversion and vibrational relaxation
factors that cause energy loss before emission
solvent polarity
excited state proton transfer
internal conversion
vibrational relaxation
equation for energy in emissions
E = hc / lamda
what is kashas rule
emission spectrum is independent of excitation wavelength
why is emission spectra the mirror image of absorption spectra
same transitions involved in both
similarities in vibrational sublevels
what is fluorescent emission wavelength sensitive to
solvent polarity
pH (excited state proton transfer
other ions eg Ca2+ and hydrogen bonding
some examples of flourophores
large conjugated organic molecules
planar
