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Nov 09

Rethinking the Jablonski Diagram

by Kenneth Hanson | Categories: chemical education, fun | (68540 Views)

I am teaching a course titled “Spectroscopic Characterization of Molecules, Materials and Photovoltaics.” The first few lectures were on molecular photophysics and included a thorough introduction of the Jablonski Diagram (For anyone interested, my lecture ppt slides are available here).

The Jablonski diagram, first introduced by Aleksander Jabłoński in 1933, is a graphical depiction of the electronic states of a molecule and the transitions between those states. The y axis of the graph is energy, which increases from the bottom (ground state or S0) to the top (singlet and triplet excited states or Sn and Tn). The transitions between the states—like excitation, internal conversion, fluorescence, intersystem crossing, etc—are depicted as arrows. Because of its simplicity, the Jablonski Diagram is a starting point for many discussions about the events that occur following electronic excitation of a molecule.

Plain Jablonski

I am new to teaching and spent a lot of time thinking about what homework I should give my students to both facilitate learning and gauge their understanding of the content. An idea hit me when I saw Mark Lorch’s revamping of the periodic table to mimic an underground rail system.

We’re all familiar with the most common depiction of the periodic table because it’s hanging in every chemistry classroom on the planet. Yet, there is no inherent physical reason we have to map the elements in that particular way. The underlying motive for this common form is to show the periodic nature of the properties of atoms as defined by their number of protons. But there are many possible ways to fulfill that goal. Non-traditional periodic tables can provide a new perspective on the relationships between atoms that are not obvious in the traditional drawing.

With that concept in mind, I decided to ask my students to rethink the Jablonski diagram.

The exact wording of the assignment was to “draw a Jablonski diagram that includes singlet and triplet excited states.” I was hoping to inspire some creativity so I pointed to the periodic table on the wall and then showed them a number of non-traditional periodic tables. I even said, “If you can express the nuances of the Jablonski Diagram through interpretive dance I would love to see it.”

No one choreographed a dance, but I was still blown away by my students’ response to the assignment. Below are some of their awesome creations.

Here is one, by Tian Zhao, depicting the lowest energy species on top and increasing energy as you go down. I like to think that it is expressing the cyclic nature of the excitation/relaxation process under steady-state conditions.

Picture1

This next submission, by Hadi Fares, is similar to the Bohr model of atoms and their electron orbitals that show the lowest energy state at the center and energy increasing outward. Unfortunately, this static image does not do justice to the animations he incorporated into the diagram.

Second image

This next diagram is similar to the one above but with additional artistic flare involving negative space. This aesthetic was inspired by “Vortex”, a game that Peilu Liu played on her ipod. The image got me thinking about the nodal planes of an orbital and whether or not it possible to graphically depict the likelihood of an electronic transition based on a comparison between the valence orbitals of a given state. Picture2

This final drawing, by Daniel Nascimento, really bumps up the information density of the Jablonski Diagram by not only including the energies of states and their transitions but also the approximate timescales of the events as shown on the x axis.

Jablonski

Much to my delight, a few students decided to really take a leap from tradition and make physical models of the Jablonski Diagram. Here is an ~12” tall work of art that was made by Maxime Matras out of aluminum rings—denoting the states (S0, T1, S1 and S2 from bottom to top)—and wires to denote the transitions between states (aluminum = excitation; copper = intersystem crossing, internal conversion, fluorescence and phosphorescence; coiled shavings = non-radiative decay).  This one now sits on my desk.

IMG_1655 small

 I even received a Jablonski diagram cake. The ground state, first singlet, second singlet and first triplet excited states are depicted in quadrants going clockwise (indicated by candy letters/numbers). The transitions are various colored lines of decorative frosting. What is really clever about this model is that the energy of the states are defined by their height from the pan. That is, the ground state is just a layer of chocolate frosting, the first excited state is a single layer of cake, and the second excited state is two layers. He also made the cake with tonic water in an effort to have it glow under a UV light. Unfortunately, I fear the cooking process destroyed the quinine and with it any possibility of glowing.  While not necessarily the most delicious of cakes, it was very creative.

 Cake image

And, finally, is “Jablinko!” This Jablonski diagram is based on the Japanese arcade and/or gambling game known as Pachinko. This photophysics-based game begins by placing a small metal ball into the S0 hole just above the lever. Pulling the lever, or exciting the molecule, shoots a ball to the top of the board into the singlet excited state. The ball (excited state) can fall one of three possible directions, NRD (non-radiative decay), ISC (intersystem crossing) or fluorescence. If it undergoes ISC, the ball can then fall into a potential well representing either non-radiative decay or phosphorescence from the triplet excited state. To top it all off, when the ball falls in to the fluorescence or phosphorescence holes it closes an electrical circuit that turns on a blue or red LED below the potential well. Those colors are the emission wavelengths for fluorescence and phosphorescence from anthracene.

Jablinko

In closing, I’d like to send a special thanks to my students. I have thoroughly enjoyed our time together and will always remember their clever responses to my first assignment.

10 comments

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  1. azmanam

    This is all levels of awesome. Very well done :)

  2. Mark

    These are just brilliant! Well done to all your students. I so want to have a go at the panchinko version. But failing that can we see a video of it in action?

    1. Kenneth Hanson

      Hey Mark,

      I would love to share a video but unfortunately Jablinko does not currently operate as described in the post. The launching spring does not have enough force to get the ball up to the singlet excited state. The red T1 block can be moved to the left and it will excite directly into the triplet but not the singlet. She wants to work on it over holiday break to fix it. If that goes well I will make sure to get a video of it.

      Sorry for the delayed response but thank you for the comment.

      Ken

  3. Matt

    Ken, This is really amazing. Congrats to your students on all of this awesomesauce-ness. And congrats to you for drawing this out of them. Really inspiring teaching!! And really really inspiring visualizations!

  4. Chad Atkins

    So awesome! I’m extremely impressed by the creativity expressed by your class – it’s easy to neglect the amazing cohesion between science and art, and I think your activity demonstrates both beautifully. Great work.

  5. Bill Peters

    about the line: “The image got me thinking about the nodal planes of an orbital and whether or not it possible to graphically depict the likelihood of an electronic transition based on a comparison between the valence orbitals of a given state”

    JB Birks goes through some MO diagram sketches to do calculations like this in one of his books. Probably in the first chapter. I don’t remember if its in “organic molecular photophysics” or “photophysics of aromatic molecules”, but its very early in one of those two texts. If I remember right, he draws the relevant MOs next to each other (typically HOMO and LUMO), does a sort of multiplication of them, mainly focusing on the signs of the orbitals, then asks about the nodal structure of the product (if totally symmetric, no transition will occur because the product with a dipole operator will then be odd, etc)

    1. Kenneth Hanson

      This is exactly the kind of imagery I was hoping for. Thank you for the references. I will see what I can dig up.

  6. Search Chemical

    This is really amazing, your students done brilliant work they describe everything very beautifully with awesome art, good to see your post.

  7. John

    There is a reason for the exact representation of the periodic table. From left to right (with the long f-series excised and placed below), the progression of elements fills the orbitals of each type and moves on to the next…
    It moves to a new line with a new quantum number, and orbitals of numbers that are lower than their energetic equivalent are placed on lower lines than the number, corresponding to the orbital energies (ie, the 3d metals are in level 4 because 3d orbitals are between 4s and 4p in energy…)

    I think you couldn’t be more wrong about the arbitration of the diagram. Any other displays that accomodate this organization would be an isomorphism of the table, and non-isomorphic representations are inferior in their information content.

  8. John

    Sorry to rain on the parade but really it is important to understand why people have settled on the representations they have, especially when only truly talented, inspiring visionaries make the choice for reasons that are steeped in experimental validation and the deepest theories known to man.

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