Photoisomerization of a 4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran analog dye: a combined photophysical and theoretical investigation

A combination of experimental and theoretical investigations of a photoisomerizable analog of 4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) dye molecule is presented. We provide evidences that the 4 main isomers and conformers of DCM...

Photo-Switchable Aggregation-Induced Emission of Bisthienylethene-Dipyrimido[2,1-b][1,3]benzothiazole Triad

A bisthienylethene-dipyrimido[2,1-b][1,3]benzothiazole (BTE-2PBT) triad has been designed and synthesized based on our recent discovery of PBTs as atypical propeller-shaped novel AIEgens. The triad not only maintains the photochromic properties of BTE moiety in solution, film, and solid state but also exhibits remarkable AIE properties. Moreover, the fluorescence of BTE-2PBT PMMA film could be modulated with high contrast by alternate UV and visible light irradiation. Photoerasing, rewriting, and non-destructive readout of fluorescent images on BTE-2PBT PMMA film well demonstrate its potential application as optical memory media.

Photofluorochromic water-dispersible nanoparticles for single-photon-absorption upconversion cell imaging

Photofluorochromic diarylethene (DAE) molecules have been widely investigated due to their excellent fatigue resistance and thermal stability. However, the poor water solubility of DAEs limits their biological applications to some extent. Herein, we reported two kinds of water-dispersible DAE nanoparticles (DAEI-NPs and DAEB-NPs), in which DAE molecules were stabilized by the amphiphilic polymer DSPE-mPEG2000 using the nanoprecipitation approach. The fabricated nanoparticles retain well-controlled luminescence and fluorescence photoswitching properties in aqueous solution, which could be reversibly switched on and off under the alternating irradiation of ultraviolet (UV) and visible light. In addition, the closed-ring isomers of DAEB-NPs performed hot-band-absorption-based photon upconversion when excited by a 593.5 nm laser. Bearing excellent photophysical properties and low cytotoxicity, DAEB-NPs were applicable for upconversion cell imaging without high-excitation power density and free from oxygen removal. Additionally, the imaging process could be switched on by regulating the photofluorochromic nanoparticles.

Photophysical Properties of 4-Dicyanomethylene-2-methyl-6-(p-dimethylamino-styryl)-4H-pyran Revisited: Fluorescence versus Photoisomerization

Although 4-dicyanomethylene-2-methyl-6-(p-dimethylamino-styryl)-4H-pyran (DCM) has been known for many decades as a bright and photostable fluorophore, used for a wide variety of applications in chemistry, biology and physics, only little attention has been paid so far to the presence of multiple isomers and conformers, namely s-trans-(E), s-cis-(E), s-trans-(Z), and s-cis-(Z). In particular, light-induced E-Z isomerization plays a great role on the overall photophysical properties of DCM. Herein, we give a full description of a photoswitchable DCM derivative by a combination of structural, theoretical and spectroscopic methods. The main s-trans-(E) isomer is responsible for most of the fluorescence features, whereas the s-cis-(E) conformer only contributes marginally. The non-emitting Z isomers are generated in large conversion yields upon illumination with visible light (e.g., 485 or 514 nm) and converted back to the E forms by UV irradiation (e.g., 365 nm). Such photoswitching is efficient and reversible, with high fatigue resistance. The E→Z and Z→E photoisomerization quantum yields were determined in different solvents and at different irradiation wavelengths. Interestingly, the fluorescence and photoisomerization properties are strongly influenced by the solvent polarity: the fluorescence is predominant at higher polarity, whereas photoisomerization becomes more efficient at lower polarity. Intermediate medium (THF) represents an optimized situation with a good balance between these two features.

Click chemistry towards thermally reversible photochromic 4,5-bisthiazolyl-1,2,3-triazoles

Three new diarylethenes were synthesized from 1,2-bis(5-methyl-2-(4-substituted-phenyl)thiazol-4-yl)ethyne and benzyl azide through Ru(I)-catalyzed Huisgen cyclization reactions. The 4,5-bisthiazolyl-1,2,3-triazoles thus prepared, which belong to the terarylene family, showed thermally reversible photochromism. The absorption maximum wavelengths of the closed forms are longer than other terarylenes reported so far. The thermal back reactions are much faster when the substituents on the terminal phenyl groups are electron-withdrawing cyano groups than when they are electron-donating methoxy groups.

Comparative photophysical investigation of doubly-emissive photochromic-fluorescent diarylethenes

Diarylethene molecules showing photochromism and fluorescence properties in both open and closed forms, associated with two different emission colors, are very promising for applications involving ratiometric emissive photoswitches. We report here a complete study on the competition between the multiple photophysical processes involved in the excited states for two sulfone derivatives of benzothiophene-based diarylethene molecules, only differing by the substituent groups on their reactive carbon (methyl for DAE-Me and ethyl for DAE-Et). Steady-state and time-resolved spectroscopy, combined with DFT and TD-DFT calculations, allow a complete determination of the kinetic constants leading to fluorescence and photoreaction pathways in different solvents, and enlighten the specific role of the substituent group in the photophysical properties due to a shielding effect against the solvation environment. The predominant role of the non-radiative deactivation processes in such a family of molecules is shown, and a tentative excited state mechanistic scheme is proposed based on femtosecond transient absorption experiments performed on the closed forms.

Multifunctional Photonic Molecular Logic Gate Based On A Biphotochromic Dyad With Reduced Energy Transfer

Using molecular logic gates (MLGs) for information processing attracts attention due to perspectives of creating molecular computers. Biphotochromic dyads are suitable models of photonic MLGs. However, they suffer from one weakness: the activity of one of the photochromes is often quenched because of Förster resonance energy transfer (FRET). Herein, we designed a dyad with reduced FRET, in which both photochromes keep their photoactivity thanks to spectral and spatial separation, allowing MLG switching between different states. This novel dyad reproduces the functionality of the full set of 16 two-input gates, as well a reversible gate-dual inverter, all gates are photonic.

Exploiting Fast Exciton Diffusion in Dye-Doped Polymer Nanoparticles to Engineer Efficient Photoswitching

Photoswitching of bright fluorescent nanoparticles opens new possibilities for bioimaging with superior temporal and spatial resolution. However, efficient photoswitching of nanoparticles is hard to achieve using Förster resonance energy transfer (FRET) to a photochromic dye, because the particle size is usually larger than the Förster radius. Here, we propose to exploit the exciton diffusion within the FRET donor dyes to boost photoswitching efficiency in dye-doped polymer nanoparticles. To this end, we utilized bulky hydrophobic counterions that prevent self-quenching and favor communication of octadecyl rhodamine B dyes inside a polymer matrix of poly(D,L-lactide-co-glycolide). Among tested counterions, only perfluorinated tetraphenylborate that favors the exciton diffusion enables high photoswitching efficiency (on/off ratio ∼20). The switching improves with donor dye loading and requires only 0.1-0.3 wt % of a diphenylethene photochromic dye. Our nanoparticles were validated both in solution and at the single-particle level. The proposed concept paves the way to new efficient photoswitchable nanomaterials.

Photoswitchable semiconductor nanocrystals with self-regulating photochromic Förster resonance energy transfer acceptors

Photoswitchable molecules and nanoparticles constitute superior biosensors for a wide range of industrial, research and biomedical applications. Rendered reversible by spontaneous or deterministic means, such probes facilitate many of the techniques in fluorescence microscopy that surpass the optical resolution dictated by diffraction. Here we have devised a family of photoswitchable quantum dots (psQDs) in which the semiconductor core functions as a fluorescence donor in Förster resonance energy transfer (FRET), and multiple photochromic diheteroarylethene groups function as acceptors upon activation by ultraviolet light. The QDs were coated with a polymer bearing photochromic groups attached via linkers of different length. Despite the resulting nominal differences in donor-acceptor separation and anticipated FRET efficiencies, the maximum quenching of all psQD preparations was 38±2%. This result was attributable to the large ultraviolet absorption cross-section of the QDs, leading to preferential cycloreversion of photochromic groups situated closer to the nanoparticle surface and/or with a more favourable orientation.

The effect of a “push–pull” structure on the turn-on fluorescence of photochromic thio-ketone type diarylethenes

A diarylethene with a six-membered ring carrying an electron-donating sulfur atom and an electron-withdrawing carbonyl group shows fluorescence in its ring-closed state.

Theoretical investigation on a series of novel S,S-dioxide diarylethenes with abnormal photochromic properties and design of new dyads

A novel diarylethene shows an abnormal conjugation system switch in a photochromic reaction, according to which new dyads were designed.

Multichromophoric sugar for fluorescence photoswitching

A multichromophoric glucopyranoside 2 bearing three dicyanomethylenepyran (DCM) fluorophores and one diarylethene (DAE) photochrome has been prepared by Cu(I)-catalyzed alkyne–azide cycloaddition reaction. The fluorescence of 2 was switched off upon UV irradiation, in proportion with the open to closed form (OF to CF) conversion extent of the DAE moiety. A nearly 100% Förster-type resonance energy transfer (FRET) from all three DCM moieties to a single DAE (in its CF) moiety was achieved. Upon visible irradiation, the initial fluorescence intensity was recovered. The observed photoswiching is reversible, with excellent photo resistance.

Photochromic–fluorescent–plasmonic nanomaterials: towards integrated three-component photoactive hybrid nanosystems

Silica-coated gold nanorods functionalized with grafted fluorescent and photochromic derivatives were synthesized and cross-coupled interactions between plasmonic, photochromic, and fluorescence properties have been demonstrated.