I am studying fluorescence anisotropy of some pentacosadiynoic acid PCDA polymer films.
I recently observed the direction of emission polarization dipole varies 90 Degree after absorption in these polymers. This is a little bit unusual.
for example, I am exciting randomly oriented PCDA polymers using vertically polarized light. Then I am collecting the emission simultaneously with to polarizer (parallel and perpendicular to the excitation). In some cases, the emission from perpendicular polarizers is higher that parallel polarizers. this cause 0 or negative anisotropy. it dictates that polarization dipole varies significantly during excited state.
I cannot explain this phenomenon.
I think the only depolarization factor is energy migration here.
( don’t worry about G factor or setup artifacts)
Dear Peter
Thanks for your answer,
My bad words, I mean, I am not worry about G factor because I measured it before precisely and I already used in my calculations.
The Higher intensity detected in perpendicular polarizers I (vh) in comparison with parallel polarizers I (vv) means negative anisotropy I (vv) - G* I(vh) /total intensity
Dear Hamid,
my knowledge about fluorescence anisotropy is quite limited, but I may be able to help you out. Can you perform a little experiment for me? Take two polarizers (can be two polaroids) with one of your films in between so that the polarization direction of one is perpendicular to the other. I assume the film is transparent in the visible? If yes, just look through it against a light source or a window. You might expect, you don't see anything because the polarizers are crossed and your film is randomly oriented (right or am I mistaken here?), but please do it anyway and report what you observe.
Best, Thomas
Hi Thomas,
Many thanks for your answer and sugessted experiment.
My films are pretty trasparent. I did the experiment and didn't see anything. It looks the polymers in films are randomly oriented.
The reason why I suggested this experiment is that random orientation alone does not mean that you don't have cross polarization. Additionally, the domains must be smaller than about a tenth of the wavelength. If not, you get double refraction in each domain (and also scattering), which can completely scramble polarization. My idea was that this might also happen to the fluorescence. I tried this with a number of polymers and also with strongly stretched ones where it is usually assumed that light polarized along the stretching direction stays linear polarized. But even in these cases the cross-polarization is far from being zero. So when you put the film between crossed polarizers and looked through they stayed completely dark? This would mean that the randomly oriented domains are smaller than about 40 nm...
- Badges
- Science topic
- Similar topics
- Mathematics