Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - BILUM (Novel applications based on organic biluminescence)

Teaser

In this project BILUM, organic small molecules are investigated that show simultaneous fluorescence and phosphorescence with high efficiency at room temperature. This turns these molecules into dual state, or as we call them, biluminescent emitters. The emission shows two...

Summary

In this project BILUM, organic small molecules are investigated that show simultaneous fluorescence and phosphorescence with high efficiency at room temperature. This turns these molecules into dual state, or as we call them, biluminescent emitters. The emission shows two characteristic emission band, split by the eneretic splitting between singlet (fluorescence) and triplet (phosphorescence) states. The fluorescence has typical decay times in the nanosecond range, whereas the phosphorescence is a quantum mechanically forbidden transition, rendering it slow with millisecond decay times.
It is the main objective to investigate this biluminescence in detail to be able to exploit these unique properties in novel applications. The project is structured in for different research directions (RDs).
In RD-A, the weakly emitting phosphorescence is the central focus. We want to understand the nature of this phosphorescence, its limitations and potential to be further increased and adjusted to possible applications.
In RD-B, we investigate effects of high population densities in such biluminescent emitters. This is central, as the phosphorescent lifetimes with millisecond values will inherently lead to saturation effects and, thus, dictate a delicate interplay between fluorescence and phosphorescence.
In RD-C, we explore biluminescence systems as sensing platforms. Here especially oxygen sensing is easily possible, as the phosphorescence is highly oxygen sensitive. With the addition of the second fluorescence channel, such biluminescence emitters intrinsically sport a reference signal.
Finally in RD-D, we utilize all or knowledge from RD-A to RD-C to design and synthesize novel biluminescent emitters. Here, the specifications are determined by the joint insights of the project and the targeted applications.

Work performed

In this first reporting period of BILUM (start to 30/09/2018), we worked on all 4 research directions. Importantly, we have estabished various experimental methodologies to fully investigate these biluminescent systems spectroscopically. Here, time and spectrally resolved photoluminescence spectroscopy has been set up (RD-A and -B), a gas mixing station has been adjusted to carry out oxygen sensing experiments (RD-C), a photoluminescence quantum yield setup has been completed (all RDs), and a glovebox and an integrated spin coater have been installed to allow for sample preparation in controlled protected environment (all RDs). All these setups and tools have been installed in new facilities of the host institution in cleanroom laboratories.
The main achievements up to now are:
1. A detailed understanding of the interplay between fluorescence and phosphorescence in thin film biluminescence samples. Here it is observed that the long-living nature of the phosphorescence leads to very high triplet state populations that give rise to saturation and bimolecular interactions.
2. The development of transparent programmable organic luminescent tags. This is a new technology we have developed in this project that allows for non-contact writing and erasing of information in thin film samples comprising biluminescent emitters.
3. The development of new biluminescent emitters (through design and synthesis) that allow for excitation using blue light. This is a key advance compared to UV-absorbing materials as the use of widely available blue and white LEDs as excitation sources is now possible.
4. The demonstration and detailed explanation of dual state energy transfer from a biluminescent donor material to a fluorescent acceptor molecule. Here, for both donor states (singlet and triplet), Förster Resonant Energy Transfer (FRET) takes place. Interestingly, and shown for the first time, the transfers happen from exactly the same molecular species but are separated by more than eight orders of magnitude in lifetime.

Final results

In the second half of the project, we will conclude various currently running projects and will intensify our research efforts between the identification of novel applications and the development of new materials. The latter point has found a very strong basis in this first reporting period and now allows to jointly exploit our know-how and expertise.
In particular, we will conclude the following studies:
1. Development of a biluminescent oxygen sensor platform.
2. Research efforts to maximize the room temperature phosphorescence
3. Development of polychrome emission systems with ultra-broadband spectra.
4. Material systems for room temperature phosphorescence under ambient conditions.
5. Integration work of biluminescence in organic electronic driving schemes.

Website & more info

More info: https://tu-dresden.de/mn/physik/iap/oh.