Bo Albinsson

Precise and reversible photoluminescence switching is highly attractive for optical memory, bioimaging, and smart displays. However, achieving broadband photoluminescence modulation through a simple and general strategy remains challenging, while the ultraviolet light requirement of most molecular photoswitches limits practical applications. Here, we achieve all-visible-light activated reversible photoluminescence modulation of quantum dots across an ultrawide spectral range of nearly 500 nm from blue to near-infrared region using diarylethene photoswitches. In the ring-open form of diarylethenes, quantum dots emitting blue, green, red, white and near-infrared light remain in the photoluminescence on-state. Under 405 nm irradiation, diarylethenes undergo ring-closure through triplet sensitization by CdS quantum dots, resulting in significant photoluminescence quenching to the off-state, with the maximum efficiency of 99.6% and an on/off ratio up to 250. Green-light irradiation reverses the diarylethenes back to the ring-open form, fully restoring the photoluminescence on-state. Our approach further enables reversible multi-level data storage and near-infrared anti-counterfeiting, highlighting the potential for smart light-responsive materials and optoelectronic devices.

Modulating photoluminescent (PL) materials is crucial for applications such as super-resolution microscopy. The combination of PL materials and photoswitches can achieve this aim by utilizing isomerization of the photoswitches. Here we report an optically PL switchable system by mixing carbon quantum dots (CQDs) and diarylethene (DAE) molecular photoswitches. The PL on/off states of CQDs, switched with alternating visible and UV light, achieve a PL on/off ratio of ∼500 and stable reversibility over 20 cycles. The mechanism of our design is revealed by PL lifetime measurements, temperature-dependent PL spectroscopy, and density functional theory (DFT) calculations, confirming that efficient static quenching and the inner filter effect between CQDs and closed DAEs are the keys to achieving such outstanding performance.

A novel photoswitchable system was developed by combining carboxylated diarylethenes (DAE 1) and CdS quantum dots (QDs), enabling all-visible light reversible interconversion of open and closed forms of DAE 1 in both aerated solution and solid-state.

Organic dyes typically have electronically excited states of both singlet and triplet multiplicity. Controlling the energy difference between these states is a key factor for making efficient organic light emitting diodes and triplet sensitizers, which fulfill essential functions in chemistry, physics, and medicine. Here, we propose a strategy to shift the singlet excited state of a known sensitizer to lower energies without shifting the energy of the triplet state, thus without compromising the ability of the sensitizer to do work. We covalently connect two to four sensitizers in such a way that their transition dipole moments are aligned in a head-to-tail fashion, but, through steric encumbrance, the delocalization is minimized between each moiety. Exciton coupling between the singlet excited states considerably lowers the first excited singlet state energy. However, the energy of the lowest triplet excited state is unperturbed because the exciton coupling strength depends on the magnitude of the transition dipole moments, which for triplets are very small. We expect that the presented strategy of designed intramolecular exciton coupling will be a useful concept in the design of both photosensitizers and emitters for organic light emitting diodes as both benefits from a small singlet-triplet energy gap.

Fluorescent base analogues (FBAs) have become useful tools for applications in biophysical chemistry, chemical biology, live‐cell imaging, and RNA therapeutics. Herein, two synthetic routes towards a novel FBA of uracil named qU (quadracyclic uracil/uridine) are described. The qU nucleobase bears a tetracyclic fused ring system and is designed to allow for specific Watson‐Crick base pairing with adenine. We find that qU absorbs light in the visible region of the spectrum and emits brightly with a quantum yield of 27 % and a dual‐band character in a wide pH range. With evidence, among other things, from fluorescence lifetime measurements we suggest that this dual emission feature results from an excited‐state proton transfer (ESPT) process. Furthermore, we find that both absorption and emission of qU are highly sensitive to pH. The high brightness in combination with excitation in the visible and pH responsiveness makes qU an interesting native‐like nucleic acid label in spectroscopy and microscopy applications in, for example, the field of mRNA and antisense oligonucleotide (ASO) therapeutics.

Visible-to-ultraviolet (UV) triplet–triplet annihilation photochemical upconversion (TTA-UC) has gained a lot of attention recently due to its potential for driving demanding high-energy photoreactions using low-intensity visible light. The efficiency of this process has rapidly improved in the past few years, in part thanks to the recently discovered annihilator compound 1,4-bis­((triisopropylsilyl)­ethynyl)­naphthalene (N-2TIPS). Despite its beneficial TTA-UC characteristics, the success of N-2TIPS in this context is not yet fully understood. In this work, we seek to elucidate what role the specific type and number of substituents in naphthalene annihilator compounds play to achieve the characteristics sought after for TTA-UC. We show that the type of substituent attached to the naphthalene core is crucial for its performance as an annihilator. More specifically, we argue that the choice of substituent dictates to what degree the sensitized triplets form excimer complexes with ground state annihilators of the same type, which is a process competing with that of TTA. The addition of more bulky substituents positively impacts the upconverting ability by impeding excimer formation on the triplet surface, an effect that is enhanced with the number of substituents. The presence of triplet excimers is confirmed from transient absorption measurements, and the excimer formation rate is quantified, showing several orders of magnitude differences between different derivatives. These insights will aid in the further development of annihilator compounds for solar energy applications for which the behavior at low incident powers is of particular significance.

We present an experimental study investigating the solvent-dependent dynamics of a 9,10-bis(phenylethynyl)anthracene monomer, dimer, and trimer. Using transient absorption spectroscopy, we have discovered that triplet excited state formation in the dimer and trimer molecules in polar solvents is a consequence of charge recombination subsequent to symmetry-breaking charge separation rather than singlet fission. Total internal reflection emission measurements of the monomer demonstrate that excimer formation serves as the primary decay pathway at a high concentration. In the case of highly concentrated solutions of the trimer, we observe evidence of triplet formation without the prior formation of a charge-separated state. We postulate that this is attributed to the formation of small aggregates, suggesting that oligomers mimicking the larger chromophore counts in crystals could potentially facilitate singlet fission. Our experimental study sheds light on the intricate dynamics of the 9,10-bis(phenylethynyl)anthracene system, elucidating the role of solvent- and concentration-dependent factors for triplet formation and charge separation.

The design of advanced optical materials based on tripletstatesrequires knowledge of the triplet energies of the molecular buildingblocks. To this end, we report the triplet energy of cyanostar (CS) macrocycles, which are the key structure-directing unitsof small-molecule ionic isolation lattices (SMILES) that have emergedas programmable optical materials. Cyanostar is a cyclic pentamerof covalently linked cyanostilbene units that form & pi;-stackeddimers when binding anions as 2:1 complexes. The triplet energies, E (T), of the parent cyanostar and its 2:1 complexaround PF6 (-) are measured to be 1.96 and2.02 eV, respectively, using phosphorescence quenching studies atroom temperature. The similarity of these triplet energies suggeststhat anion complexation leaves the triplet energy relatively unchanged.Similar energies (2.0 and 1.98 eV, respectively) were also obtainedfrom phosphorescence spectra of the iodinated form, I-CS, and of complexes formed with PF6 (-) andIO(4) (-) recorded at 85 K in an organic glass.Thus, measures of the triplet energies likely reflect geometries closeto those of the ground state either directly by triplet energy transferto the ground state or indirectly by using frozen media to inhibitrelaxation. Density functional theory (DFT) and time-dependent DFTwere undertaken on a cyanostar analogue, CSH, to examinethe triplet state. The triplet excitation localizes on a single olefinwhether in the single cyanostar or its & pi;-stacked dimer. Restrictionof the geometrical changes by forming either a dimer of macrocycles,(CSH)(2), or a complex, (CSH)(2)& BULL;PF6 (-), reduces the relaxationresulting in an adiabatic energy of the triplet state of 2.0 eV. Thisstructural constraint is also expected for solid-state SMILES materials.The obtained T-1 energy of 2.0 eV is a key guide line forthe design of SMILES materials for the manipulation of triplet excitonsby triplet state engineering in the future.

Green‐to‐blue triplet–triplet annihilation photon upconversion with the well‐studied upconversion pair 9,10‐diphenylanthracene (DPA)/platinum octaethylporphyrin (PtOEP) was used to reversibly drive the photoisomerization of diarylethene (DAE) photoswitches by using visible light. By carefully selecting the kinetic and spectral properties of the molecular system as well as the experimental geometry, a single green light source can be used to selectively trigger both the ring‐opening and the ring‐closing reactions, whilst also inducing fluorescence from the colored closed isomer that can be used as a readout to monitor the isomerization process in situ. The upconversion solution and the DAE solution are kept physically separated, allowing them to be characterized both concomitantly and individually without further separation processes. The ring‐closing reaction using upconverted photons was quantified and compared to the efficiency of direct isomerization with ultraviolet light.

A simple, efficient and general approach for all-visible-light switching of photochromic diarylethenes is developed through triplet sensitization from CdS nanocrystals, which has high potential for all-visible-light activated optoelectronics.