This time I will show a few "quantum images". Hydroxybenzoquinoline is kind of a cool molecule because it shows excited state intramolecular proton transfer. After UV excitation the proton is transferred from the oxygen to the nitrogen. This happens on a time scale of about 30 fs because the process is essentially barrierless. This is a time scale where you can do ab-initio molecular dynamics. And with modern LASER pulses you can also examine it experimentally. That's why these molecules have been rather popular recently.
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgnay-9uROg-DriGVnUFXqMClNDTgIk85eFF5O5xg3Me9pEb10n83_enpoWd8yN4px5Mh4NX2yIX5RXM7b6vMqCI56X8uOqB7ErHfK4af5fC1tREIFlFDE1_1zZa4qSuhsIvQFAZyF28tw/s400/HBQ_scheme.png)
What I want to show here are the orbitals because I think they look kind of cool. What you see are the two highest occupied orbitals (n, π) and the lowest unoccupied orbital (π*). The two important excitations are just between these orbitals leading to the ππ* and nπ* states respectively.
Related to the proton transfer it can be seen that the π* LUMO has more density on the N which increases its basicity to help it catch the proton.
Something else that is interesting is that a non-bonding orbital (coming from MO theory) really looks a lot like the free electron pair you would talk about in VB theory. I was arguing with an analytical chemistry professor once that he should not interchange the terms non-bonding orbital and free electron pair because they come from different approaches. Now I see that he was right but I did not believe him then because he was from analytical chemistry.
Enol (ground state) | | Keto (ππ* state) |
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjduwdbN8HMpzVHpscpQ6Kby-Uqi8CT0XdGGFP7GyrK3iNs3iwws63so4W0n7YwlXRc-127ZqfWpE-HSMdcZ_FVmELAh1F1Qsuh5l3LPQZNmmE9ITTxFuLeUSta6m45o11wpTN6nZkwED0/s200/orb37.jpg) | π* | ![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjMgr91LufMlrZwqo2yWi-VGny_YVhvfOh_SQ0KyRyzwzn321_smPmijRHGH8zdyCuLzqdcHUzS8WmrbesoBAI8XaiZ2lAkDofNdPOLycUXTE2hEY-NusUJ6p-AkrJ_XvW22iwtpuXpWSQ/s200/pi_st.jpg) |
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhMjpuFfoF-18ujjzsh4pdP41ecI_HhFfBkBpZSNU9IZuev1rVWqCfVM3H1qPkuoRyJILre7SZpQydJ4pGpU1PT036LOpq72CL2wPk4l6M_mFimvZOAxKTLuCXs561Z1I13WzJX3VYObFw/s200/orb36.jpg) | π | ![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjFSy18FQBMvblbq09TspfG64LbJXPPCtyFq1BWyYnOazxZMh9QjVOhMVdcSKF0WnE0s0fvZ6NvE4lLzdLi8kTksJHmcGThaFlMwLv2qQIMADO3M5GKzulLp110PVSTpY4j4n1BLSrgE-g/s200/pi.jpg) |
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiGvMLTICOnpU4_y4CFMpYyHtOzweI1B5AI_r2gVXbVQ-5lHTnJ9E8yZzfdAckVwYmeSQaytGkKSXqBz-yBywhS6HddjAuEbt8JBqXHFXvzuVKYGm0DzmKHCSnF-R0XWfRq_G_qbUy9X9k/s200/orb35.jpg) | n | ![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEidUOwmSej0qzAi1v2gO4V0RojKH7hy3DfdGp4TdLDCAU0pFcXGP_O_igoicbq1CRJzEV5aXyIP4vTMWzQPcPCaICn897rioDCffCw_mQyuizEr4P_M0isgSUc98ZR3D0ygjTU2NBvirP0/s200/n.jpg) |
Just a short summary of the software: the orbitals are actually from semi-empirical
DFTB. And the pictures are made with
VMD.
2 comments:
Hello,
I have recently read a paper from Marcus Elsner et al. in PNAS (http://www.pnas.org/content/105/50/19672.abstract?sid=b2adfe84-c3f9-438e-806f-0b22f7f0afea) where they claim that their DFTB method can reproduce DFT(w. B3-LYP) calculations. They applied this to a small part of a protein. Have you done any other calculation to test the DFTB method for the keto/Enol stuff?
How did you do the dynamics? Newton? Langevin? Wavefunction propagation?
It's not that easy to believe in results when you not know about the used methods :)
Greetings
Till
actually this is not really related to my group's paper where they used TDDFT/B3LYP with Newtonian and wave packet dynamics (http://dx.doi.org/10.1016/j.chemphys.2007.10.021)
we have some good experience with DFTB for modelling solvation in the ground state including hydrogen bonds (that is not really my topic though). here the topic was time-dependent DFTB for excited states and that is a whole different question. TD-DFTB is amazing because it's so fast. but since already TDDFT causes problems in many cases it is even more of an issue here
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