The aggregation of conjugated polymers and electronic coupling of chromophores play a central role in the fundamental understanding of light and charge generation processes. Here we report that the predominant coupling in isolated aggregates of conjugated polymers can be switched reversibly between H-type and J-type coupling by partially swelling and drying the aggregates. Aggregation is identified by shifts in photoluminescence energy, changes in vibronic peak ratio, and photoluminescence lifetime. This experiment unravels the internal electronic structure of the aggregate and highlights the importance of the drying process in the final spectroscopic properties. The electronic coupling after drying is tuned between H-type and J-type by changing the side chains of the conjugated polymer, but can also be entirely suppressed. The types of electronic coupling correlate with chain morphology, which is quantified by excitation polarization spectroscopy and the efficiency of interchromophoric energy transfer that is revealed by the degree of single-photon emission.

Simple and cheap organic thin films turn into high-quality programmable tags through writing and erasing with light only.

population of the excited triplet via a spinforbidden intersystem crossing from singlet to triplet. Moreover, the excited triplet can be quenched quite easily by molecular oxygen or deactivated through nonradiative pathways ( Figure 1A). In the literature, two main approaches have been developed to overcome those issues and achieve persistent RTP in aerated atmosphere. In any case, the phosphors must be contained in a rigid environment, inducing a restriction of molecular motion, be it a crystalline structure [11][12][13] or the use of an external host trapping the luminophore in the amorphous phase. [14,15] In both systems, much progress has been achieved, and efficient materials have been developed reporting long-lasting phosphorescence and high phosphorescence quantum yield. In 2017, Shoji et al. revealed the exceptional phosphorescence properties of a series of simple crystalline arylboronic esters, with lifetimes up to 1.73 s, which is-to the best of our knowledge-one of the longest values ever reported for metal-free organic phosphors. [16] Earlier this year, Su et al. designed an organic molecule that is able to participate in multiple hydrogen bondings. After dispersion into polyvinyl alcohol (PVA) to create drop-coating thin films and long irradiation under strong UV light (65 min, 254 nm), an intense phosphorescence (Φ p up to 11.23%) associated with a long lifetime (up to 0.71 s) could be observed at room temperature in aerated atmosphere. In fine, these films could be used to print and encode information. [17] These examples, as for most of the studies reporting URTP pure organic systems described in the literature, work only with excitation in the UV range to trigger the phosphorescence response. This represents a clear limitation and makes these materials hardly suitable for potential mass commercial purpose. The only exception has been reported by Huang and co-workers in 2017. [18] In this work, the authors describe the rational design of new phosphorescent organic crystalline powders, characterized by very long emission lifetimes (up to 0.84 s), due to the derivatives ability to form H aggregates. For one crystalline target with absorption strength ranging up to 450 nm, phosphorescence could be obtained after excitation with a commercial white light-emitting diode (LED). But the long-term stability of such crystalline structures is unclear and unreliable, and the elaboration of thin films from such materials can be laborious, which makes them impractical for the development of smart tags or security devices.The development of organic materials displaying ultralong room-temperature phosphorescence (URTP) is a material design-rich research field with growing interest recently, as the luminescence characteristics have started to become interesting for applications. However, the development of systems performing under aerated conditions remains a formidable challenge. Furthermore, in the vast majority of molecular examples, the respective absorption bands of the compounds are in the near ultraviolet (...

In recent years, there has been a growing interest in purely organic materials showing ultralong room‐temperature phosphorescence with lifetimes in the range of seconds. Still, the longest known phosphorescence lifetimes are only achieved with crystalline systems so far. Here, a rational design of a completely new family of halogen‐free organic luminescent derivatives in amorphous matrices, displaying both conventional fluorescence and phosphorescence is reported. Hydrogen bonding between the newly developed emitters and an ethylene‐vinyl alcohol copolymer (Exceval) matrix, which efficiently suppresses vibrational dissipation, enables bright long‐lived phosphorescence with lifetimes up to 2.6 s at around 480 nm. The importance of the chosen matrix is shown as well as the implementation in an organic programmable luminescent tag.

For almost 70 years, Förster resonance energy transfer (FRET) has been investigated, implemented into nowadays experimental nanoscience techniques, and considered in a manifold of optics, photonics, and optoelectronics applications. Here, we demonstrate for the first time simultaneous and efficient energy transfer from both donating singlet and triplet states of a single photoluminescent molecular species. Using a biluminescent donor that can emit with high yield from both excited states at room temperature allows application of the FRET framework to such a bimodal system. It serves as an exclusive model system where the spatial origin of energy transfer is exactly the same for both donating spin states involved. Of paramount significance are the facts that both transfers can easily be observed by eye and that Förster theory is successfully applied to state lifetimes spanning over 8 orders of magnitude.