and this is fully consistent with the experimental findings and earlier theoretical
predictions [67]. Note, that there are small deviations in the absorption maxima of
various GFP variants. In particular, the maximum of the wild-type GFP (471 nm at
77 K and 477 nm at 300 K) [66] is blue-shifted compared to those of the S65T
structure (489 nm) [68, 69] and of the enhanced S65T/F64L GFP mutant (492 nm)
[70] at 300 K.
Importantly, the PD-active modes are those that are excited upon the S 0 !S 1
transition. Upon excitation of the totally symmetric stretching modes in the blue
part of the spectrum, electron ejection becomes a dominating channel (see
Fig. 5.15). On the other hand, out-of-pane twisting induces a non-adiabatic coupling
between the S 1 and S 0 states in internal conversion. Such a mode-specificity in the
intrinsic photoresponse of the chromophore should have a direct implication to the
diverse functioning of the GFP proteins.
5.5
Concluding Remarks
Here, we have discussed how recent developments in action and photoelectron
spectroscopy combined with state-of-the-art electronic structure theory give the
detailed insights into photo-initiated quantum dynamics of the isolated GFP chromophore anion. It is worth noting, that this anionic chromophore exhibits a remarkable efficiency in the non-adiabatic couplings between the electronic and nuclear
motion in the excited-state decay channels. This results in a dual energy transfer
from the electrons to the nuclei in internal conversion occurring through the S 1 /S 0
conical intersection and from the nuclei to the electrons in vibrational
autodetachment out of the S 1 state, which has a bound character in the FranckCondon region.
The mode-specificity revealed in the excited-state decay channels [36] might
have possible implications to the functioning of the GFP proteins. The wellestablished paradigm in the functioning of the fluorescent proteins is the IC
suppression by the protein environment. However, a new emerging scenario [19]
is based on the active role of the GFP proteins containing tyrosine-based
chromophores in photochemical reactions. Remarkably, the modes that are excited
upon photoabsorption should also be most active in the possible electron transfer
reactions, involving the GFP oxidation, since the S 1 /D 0 minimum displacements are
large along these high-frequency stretching modes, similar to the gas phase [36].
The electron transfer through a resonant tunneling, involving GFPs as electron
donors, should then be accompanied by nuclear rearrangements along these particular modes.
The biological function is closely connected to the ways, by which the protein
environment tunes the intrinsic photoresponse of their chromophores and guides
their excited-state evolution. Many GFP proteins prohibit internal conversion of
their chromophores, thus possibly directing the decay towards the fast electron
transfer governed by the most Franck-Condon active stretching modes.
5 Photo-initiated Dynamics and Spectroscopy of the Deprotonated Green. . .
99
predictions [67]. Note, that there are small deviations in the absorption maxima of
various GFP variants. In particular, the maximum of the wild-type GFP (471 nm at
77 K and 477 nm at 300 K) [66] is blue-shifted compared to those of the S65T
structure (489 nm) [68, 69] and of the enhanced S65T/F64L GFP mutant (492 nm)
[70] at 300 K.
Importantly, the PD-active modes are those that are excited upon the S 0 !S 1
transition. Upon excitation of the totally symmetric stretching modes in the blue
part of the spectrum, electron ejection becomes a dominating channel (see
Fig. 5.15). On the other hand, out-of-pane twisting induces a non-adiabatic coupling
between the S 1 and S 0 states in internal conversion. Such a mode-specificity in the
intrinsic photoresponse of the chromophore should have a direct implication to the
diverse functioning of the GFP proteins.
5.5
Concluding Remarks
Here, we have discussed how recent developments in action and photoelectron
spectroscopy combined with state-of-the-art electronic structure theory give the
detailed insights into photo-initiated quantum dynamics of the isolated GFP chromophore anion. It is worth noting, that this anionic chromophore exhibits a remarkable efficiency in the non-adiabatic couplings between the electronic and nuclear
motion in the excited-state decay channels. This results in a dual energy transfer
from the electrons to the nuclei in internal conversion occurring through the S 1 /S 0
conical intersection and from the nuclei to the electrons in vibrational
autodetachment out of the S 1 state, which has a bound character in the FranckCondon region.
The mode-specificity revealed in the excited-state decay channels [36] might
have possible implications to the functioning of the GFP proteins. The wellestablished paradigm in the functioning of the fluorescent proteins is the IC
suppression by the protein environment. However, a new emerging scenario [19]
is based on the active role of the GFP proteins containing tyrosine-based
chromophores in photochemical reactions. Remarkably, the modes that are excited
upon photoabsorption should also be most active in the possible electron transfer
reactions, involving the GFP oxidation, since the S 1 /D 0 minimum displacements are
large along these high-frequency stretching modes, similar to the gas phase [36].
The electron transfer through a resonant tunneling, involving GFPs as electron
donors, should then be accompanied by nuclear rearrangements along these particular modes.
The biological function is closely connected to the ways, by which the protein
environment tunes the intrinsic photoresponse of their chromophores and guides
their excited-state evolution. Many GFP proteins prohibit internal conversion of
their chromophores, thus possibly directing the decay towards the fast electron
transfer governed by the most Franck-Condon active stretching modes.
5 Photo-initiated Dynamics and Spectroscopy of the Deprotonated Green. . .
99