Post Tagged with: "photophysics"

Update: Photo Friday (#picpickoftheweek)

In January the Hanson Research Group (@HansonFSU) introduced Photo Friday, a twitter-based ‘best picture of the week’ (#picpickoftheweek). Since then my students have created an amazing collection of photographs depicting our research, equipment, and chemicals. I’d like to highlight my six favorite photos so far (in no particular order).

In the first picture a reaction mixture, under UV light, is cooled to -78°C using a dry ice-acetone bath. Emission is usually more intense when molecules are cooled because it slows vibrational relaxation (non-radiative decay).

rxnThe second picture shows a fluorescent dye in dichloromethane being poured into an Erlenmeyer flask under UV-light (365 nm).

PourPicture three offers a glimpse inside the excitation monochromator of our fluorometer. The device is composed of a grating, to disperse the white light (xenon lamp source) into its components, and mirrors to direct the monochromatic light toward the sample.

MonochrometerPhoto four is a very stylized look at one of our variable magnetic field cuvette holders. The knob you see in the bottom right is used to move the neodymium magnets closer or further away from the cuvette. With the magnets next to the cuvette we get a field of about 0.35 T at the point of emission. The dry ice adds an ethereal feel to the photo but more importantly allows us to see the laser beam.

Laser through magnetic fieldEmission from molecules bound to semiconducting films depend on the energy of the chromophore, the conduction band of the semiconductor, the solvent, and other variables. Photo five demonstrates how the distance between the molecule and the semiconductor can affect emission intensity.

Film emissionThe concentration gradients that occur when a solid dissolves in solvent is easy to visualize using fluorescent molecules, as shown in picture six. Eventually the color will even out but the process is relatively slow without stirring.

DissolveFollow us on twitter (@HansonFSU) for more more of our #picpickoftheweek.

By May 21, 2014 0 comments Uncategorized

Photo Friday (#picpickoftheweek)

My graduate student, Sean Hill, became the Hanson Research Group twitter account manager last week. We first talked about what is and isn’t acceptable to post on the internet. Then Sean explained to me the nuances of hash tags and how I’ve underutilized them.  He also suggested something brilliant: a photo of the week.

One of the things I like most about doing research in molecular photophysics is the beautiful color chemistry. Now, every Friday, Sean will tweet (#picpickoftheweek) our best photo taken during the prior week. Our first image (below) is very fun and depicts a photon upconversion solution.

Upconversion

This image shows green laser pointer light (532 nm) causing blue (~430 nm) emission from the solution.  What makes this image really interesting, from a photophysics standpoint, is that we’re  observing the conversion of lower energy green photons into higher energy blue photons.

The reverse—higher energy blue light turning into lower energy green light—is easy. Many molecules absorb a single high energy photon and then emit a single lower energy photon with some energy lost in the process due to vibrational relaxation.  The more difficult green-to-blue light change depicted above is only possible if we combine the energy from two green photons to produce one higher energy blue photon.  This process is known as photon upconversion.

While it can be observed in inorganic nanoparticles, the solution above is a mixture of two types of molecules that undergo excitation, energy transfer, triplet-triplet annihilation and then emission.  Our research group is interested in studying these upconversion systems because they could potentially provide a mechanism to harness low energy light and increase the theoretical maximum solar cell efficiency from 33% to >40%. If you’re interested in learning more about photon upconversion through triplet-triplet annihilation, here is a good review article.

Follow us, @HansonFSU, on twitter for more molecular color chemistry.

By January 18, 2014 4 comments fun