Charge Transfer Character Research Articles

Mechanism of Ultrafast Triplet Exciton Formation in Single Cocrystals of π-Stacked Electron Donors and Acceptors.

Ultrafast triplet formation in donor-acceptor (D-A) systems typically occurs by spin-orbit charge-transfer intersystem crossing (SOCT-ISC), which requires a significant orbital angular momentum change and is thus usually observed when the adjacent π systems of D and A are orthogonal; however, the results presented here show that subnanosecond triplet formation occurs in a series of D-A cocrystals that form one-dimensional cofacial π stacks. Using ultrafast transient absorption microscopy, photoexcitation of D-A single cocrystals, where D is coronene (Cor) or pyrene (Pyr) and A is N,N-bis(3'-pentyl)-perylene-3,4:9,10-bis(dicarboximide) (C5PDI) or naphthalene-1,4:5,8-tetracarboxydianhydride (NDA), results in formation of the charge transfer (CT) excitons Cor•+-C5PDI•-, Pyr•+-C5PDI•-, Cor•+-NDA•-, and Pyr•+-NDA•- in <300 fs, while triplet exciton formation occurs in τ = 125, 106, 484, and 958 ps, respectively. TDDFT calculations show that the SOCT-ISC rates correlate with charge delocalization in the CT exciton state. In addition, time-resolved EPR spectroscopy shows that Cor•+-C5PDI•- and Pyr•+-C5PDI•- recombine to form localized 3*C5PDI excitons with zero-field splittings of |D| = 1170 and 1250 MHz, respectively. In contrast, Cor•+-NDA•- and Pyr•+-NDA•- give triplet excitons in which |D| is only 1240 and 690 MHz, respectively, compared to that of NDA (2091 MHz), which is the lowest energy localized triplet exciton, indicating that the Cor-NDA and Pyr-NDA triplet excitons have significant CT character. These results show that charge delocalization in CT excitons impacts both ultrafast triplet formation as well as the CT character of the resultant triplet states.

Improving Near-Infrared Emission of meso-Aryldipyrrin Indium(III) Complexes via Annulation Bridging: Excited-State Dynamics.

Using non-adiabatic dynamics and Redfield theory, we predicted the optical spectra, radiative and nonradiative decay rates, and photoluminescence quantum yields (PLQYs) for In(III) dipyrrin-based complexes (i) with electron-withdrawing (EW) or electron-donating (ED) substituents on the meso-phenyl group and (ii) upon fusing the pyrrin and phenyl rings via saturated or unsaturated bridging to increase structural rigidity. The ED groups lead to a primary π,π* character with a minor intraligand charge transfer (ILCT) contribution to the emissive state, while EW groups increase the ILCT contribution and red-shift the luminescence to ∼1.5 eV. Saturated annulation enhances the PLQYs for complexes with primary π,π* character compared to those of the non-annulated and unsaturated-annulated complexes, while both unsaturated and saturated annulation decrease the PLQYs for complexes with primary ILCT character. We found that PLQY improvement goes beyond a simple concept of structural rigidity. In contrast, the charge transfer character of excitonic states is a key parameter for engineering the NIR emission of In(III) dipyrrin complexes.

Excitation energy transfer and vibronic coherence in intact phycobilisomes.

The phycobilisome is an oligomeric chromoprotein complex that serves as the principal mid-visible light-harvesting system in cyanobacteria. Here we report the observation of excitation-energy-transfer pathways involving delocalized optical excitations of the bilin (linear tetrapyrrole) chromophores in intact phycobilisomes isolated from Fremyella diplosiphon. By using broadband multidimensional electronic spectroscopy with 6.7-fs laser pulses, we are able to follow the progress of excitation energy from the phycoerythrin disks at the ends of the phycobilisome's rods to the C-phycocyanin disks along their length in <600 fs. Oscillation maps show that coherent wavepacket motions prominently involving the hydrogen out-of-plane vibrations of the bilins mediate non-adiabatic relaxation of a manifold of vibronic exciton states. However, the charge-transfer character of the bilins in the allophycocyanin-containing segments localizes the excitations in the core of the phycobilisome, yielding a kinetic bottleneck that enables photoregulatory mechanisms to operate efficiently on the >10-ps timescale.

PH assisted modulation in the binding affinity for BODIPY-benzimidazole conjugate with anionic cyclodextrin

Modulation in the properties of chromophoric guest dyes involving non-covalent supramolecular interactions of various macrocyclic hosts are the intense topics of current research. In this study we report interaction of a sulfobutylether-β-cyclodextrin (SBEβCD) host in modulating the photophysical as well as prototropic properties of an inhouse synthesized BODIPY-benzimidazole conjugate dye, abbreviated as BDZ. The SBEβCD host displays substantially different binding strengths for the protonated and unprotonated forms of the prototropic BDZ dye, inducing a large upward pKa shift for the dye. Furthermore, structural confinement of the dye upon binding with the host leads to substantial enhancement in the fluorescence intensity and lifetime for both the prototropic forms of the dye. This can be attributted to the reduction in the non-radiative deexcitation process for the bound dye. Fluorescence enhancements are also accompanied with large increase in fluorescence anisotropy decay times, substantiating dye-host binding. Since unprotonated BDZ in free state is extremely weak in emission due to its intramolecular charge transfer (ICT) character, its fluorescence enhancement on binding to SBEβCD is found to be more pronounced than protonated BDZ. Importantly, emission of BDZ–SBEβCD system appears in the green region of visible spectrum, implying the immense prospect of the system for fluorescence-based sensor and imaging applications in different biological studies.

Benefits of the Exciplex-like Framework in Reducing the Singlet-Triplet Energy Difference: A Theoretical Perspective on the Role of the Exciton Binding Energy

By means of post-Hartree-Fock and density functional theory calculations, we compare the exciplex-like U-type and conventional S-type thermally activated delayed fluorescence emitters which are composed of electron-donor (D), linker (L), and electron-acceptor (A) units: 10-phenyl-9,10-dihydroacridine, fluorene, and 2,4,6-triphenyl-1,3,5-triazine analogues, respectively. We found that the singlet-triplet energy difference, ΔEST, consistently decreases in going from the S-type emitters to their U-type counterparts, and this reduction in ΔEST is ascribed to the substantially more stable S1 state of the latter, while their T1 states remain similar in energy. Natural transition orbital pictures and excitation energy decomposition analyses demonstrate that the S1 states of the emitters are dominated by the charge transfer (CT) character and stabilized by the exciton binding energy, EB, which substantially enhances when the hole and electron are in close proximity. Without relying on the vague notion of through-space vs through-bond CT characters, we clearly showed that the exciplex-like molecular framework can effectively reduce ΔEST by taking advantage of the short distance between the D and A units and subsequently reinforcing EB for the D-to-A CT state.

The Full d3-d5 Redox Series of Mononuclear Manganese Complexes: Geometries and Electronic Structures of [Mn(dgpy)2]n.

Although manganese ions exhibit a rich redox chemistry, redox processes are often accompanied by structural reorganization and a high propensity for ligand substitution, so that no complete structurally characterized manganese(II,III,IV) complex series without significant ligand sphere reorganization akin to the manganese(II,III,IV) oxides exists. We present here the series of pseudo-octahedral homoleptic manganese complexes [Mn(dgpy)2]n+ (n = 2-4) with the adaptable tridentate push-pull ligand 2,6-diguanidylpyridine (dgpy). Mn-N bond lengths and N-Mn-N bond angles change characteristically from n = 2 to n = 4, while the overall [MnN6] coordination sphere is preserved. The manganese(III) complex [Mn(dgpy)2]3+ exhibits a Jahn-Teller elongated octahedron and a negative D = -3.84 cm-1. Concomitantly with the consecutive oxidation of [Mn(dgpy)2]2+ to [Mn(dgpy)2]4+, the optical properties evolve with increasing ligand-to-metal charge transfer character of the absorption bands culminating in the panchromatic absorption of the purple-black manganese(IV) complex [Mn(dgpy)2]4+.

Phosphonium-Based Ionic Thermally Activated Delayed Fluorescence Emitters for High-Performance Partially Solution-Processed Organic Light-Emitting Diodes

Phosphonium-Based Ionic Thermally Activated Delayed Fluorescence Emitters for High-Performance Partially Solution-Processed Organic Light-Emitting Diodes

Molecular logic with ferrocene-rylene conjugates: A comparison of naphthalenediimide, naphthalimide and perylenediimide Pourbaix sensor designs

Four molecules designed as Pourbaix sensors with rylene dyes (naphthalenediimide, 4-amino-1,8-naphthalimide, perylenediimide) are compared. Each molecule is constructed modularly according to an electron-donor–spacer–fluorophore–spacer–receptor format based on photoinduced electron transfer (PET). The modules consist of ferrocene as the electron donor, a tertiary alkyl amine as the proton receptor, and a rylene dye as the fluorophore connected by a methylene and ethylene spacer, respectively. The proton and oxidant-induced fluorescent spectral changes of the 4-amino-1,8-naphthalimide models include internal charge transfer (ICT) character. Two of the discussed logic gates switch on emitting fluorescence in the presence of acid (H+) and oxidant (Fe3+) according to two-input AND logic, while two of the logic gates remain off according to two-input PASS 0 logic.

Connecting two intrinsic electron donor and acceptor moieties through distinctive π-bridging units to explore their optical and nonlinear optical properties

Boraphenalene and pyrido(2,1,6-de)quinolizine moieties are intrinsically electron acceptor and donor groups, owing to their electron deficient and electron rich characteristics, respectively. In the current study, quantum computations are executed for investigating the charge transfer character and nonlinear optical (NLO) response for various combinations of boraphenalene and pyrido(2,1,6-de)quinolizine derivatives. The effect of various π-conjugated connectors i.e. direct ring attachment (1AB), ethylene (2AB), acetylene (3AB) and phenylene (4AB) units on optical and NLO properties were studied. Density functional theory (DFT) techniques are employed for computing the responses properties for designed compounds (A, B, 1AB, 2AB, 3AB and 4AB). From the studied compounds, 4AB exhibits the leading average second-order NLO polarizability of 954.8 × 10-30 esu, which was about 148 times greater than para-Nitroaniline (p-NA) molecule (a typical push-pull NLO molecule). The source of greater values of hyperpolarizability is tracked through TD-DFT computations where electronic transitions having better oscillator strengths along with lower transition energies are seen more contributing in hyperpolarizability. Additionally, the assessment of electrostatic potentials (ESPs), density of states (DOS), frontier molecular orbitals (FMOs) and transition density matrix (TDM) diagrams provide a molecular-level insight into the structures and their relationship to NLO properties of designed derivatives. Hence, the current investigation would arouse the curiosity of other scientists in the field for such different and novel strategy for designing NLO materials.

Rhenium(I) Complexes with Neutral Monodentate Coligands and Monoanionic 2-(1,2,4-Triazol-5-yl)pyridine-Based Chelators as Bidentate Luminophores with Tunable Color and Photosensitized Generation of 1O2: An Integrated Case Study Involving Photophysics and Theory.

In this work, we describe the synthesis as well as structural, photophysical, and theoretical investigation of a new coordination chemical concept involving rhenium(I) complexes bearing monoanionic 1,2,4-triazolylpyridine-based bidentate chromophores. The X-ray diffractometric analysis of single crystals revealed particular packing features: the trifluoromethylated exemplar displayed two kinds of arrangements of the coordination centers, where the bidentate ligands at the edges of the unit cell are staggered parallel to each other, whereas those inside show antiparallel stacking with respect to the external ligands. On the other hand, the complexes bearing an adamantyl substituent yield a linear arrangement, where the bulky moiety of one luminophore points to the pyridine center of the adjacent ligand of the neighboring complex while including methanol molecules hydrogen-bonded to the triazolato unit. We observed that the photophysical properties of the complexes (photoexcited-state lifetimes, photoluminescence maxima and quantum yields) can be adjusted by tuning of the substitution pattern at the bidentate luminophore as well as by variation of the monodentate coligand. The photoluminescence spectra and photoexcited-state lifetimes of the crystalline phases were measured by phosphorescence lifetime micro(spectro)scopy. Interestingly, the vibrationally resolved emission spectra of the crystals closely resemble those of diluted frozen glassy matrixes at 77 K, in contrast with the broad bands observed in amorphous solids and in fluid solutions, where the charge-transfer character is enhanced. While the photoluminescence quantum yields (ΦL) reach up to 15%, the complexes are able to attain up to 55% efficiency regarding the photosensitization of 1O2 (ΦΔ), depending on the combination of luminophore and coligand. Theoretical calculations showed that the photoexcited triplet (T1) state has a metal-ligand-to-ligand charge-transfer character, where promotion to the excited electronic configuration shortens the Re(I)-N bond involving the bidentate triazolylpyridine while stretching the three fac-CO-Re(I) bonds as well as the linkage to the axial monodentate coligand. The calculated vertical (Evl) and 0-0 (E(0-0)) radiative transition energies are in very good agreement with the experimental values (Eexplum).

Dual Z-scheme core-shell PANI-CeO2-Fe2O3-NiO heterostructured nanocomposite for dyes remediation under sunlight and bacterial disinfection

Nowadays, environmental pollution due to discharge of organic pollutants from food, textile, and pharmaceutical industries into clean water and development of contagious diseases due to pathogenic organisms provide impetus to material researcher to fabricate novel design for efficient photocatalyst and antimicrobial agents. In this regard, designing a core-shell heterojunction catalyst based on metal oxides is considered an auspicious approach. In present study, combating the problems of singular oxides, core-shell PANI-CeO2-Fe2O3–NiO nanocomposite (PCFN) and CeO2–Fe2O3–NiO nanocomposite (CFN) was synthesized through sol-gel and oxidative polymerization route with cetyletrimethylammonium bromide (CTAB) as surfactant. The XRD, FTIR, and Raman confirmed the formation of nanocomposites with core-shell morphology composed of PANI (shell) and oxides (Core) in PCFN with a particle size of 52 nm (TEM). Surprisingly, PCFN has lower band gap, e−/h+ recombination, and larger charge transfer character than CFN. The decomposition test using MB and MO dyes showed that PCFN degraded 99%, 98%, while CFN degraded only 73% and 54%, respectively, under 50 min sunlight illumination. The reusability was assessed up to 7th cycle for PCFN. The influence of operational parameters (catalyst dose, dye concentration, pH) was tested for PCFN. Further, the antimicrobial action against S. aureus (gram + ve), E. coli (gram -ve) were also tested. The supreme performance of PCFN has been credited to heterostructure dual Z-scheme formation and core-shell morphology supported with PANI, which suppresses the e−/h+ recombination process by promoting their separation. The present finding indicated that the PCFN is a promising modifier for bacterial disinfection and acts as a superb photocatalyst through core-shell formation with PANI support.

Divergent Approach for Tris-Heteroleptic Cyclometalated Iridium Complexes Using Triisopropylsilylethynyl-Substituted Synthons.

Bis-heteroleptic cyclometalated iridium complexes of the form Ir(La)2(acac), where La is a substituted 2-phenylpyridine derivative and acac is an acetylacetonato ligand, are a useful class of luminescent organometallic complexes for a range of applications. Related tris-heteroleptic complexes of the form Ir(La)(Lb)(acac) offer the potential advantage of greater functionality through the use of two different cyclometalated ligands but are, in general, more difficult to obtain. We report the synthesis of divergent bis- and tris-heteroleptic triisopropylsilylethynyl-substituted intermediate complexes that can be diversified using a “chemistry-on-the-complex” approach. We demonstrate the methodology through one-pot deprotection and Sonogashira cross-coupling of the intermediate complexes with para-R-aryliodides (R = H, SMe, and CN). The photophysical and electrochemical behaviors of the resultant bis- and tris-heteroleptic complexes are compared, and it is shown that the tris-heteroleptic complexes exhibit subtly different emission and redox properties to the bis-heteroleptic complexes, such as further red-shifted emission maxima and lower extinction coefficients, which can be attributed to the reduced symmetry. It is demonstrated, supported by DFT and time-dependent DFT calculations, that the charge-transfer character of the emission can be altered via variation of the terminal substituent; the introduction of an electron-withdrawing cyano group in the terminal position leads to a significant red shift, while the introduction of an SMe group can substantially increase the emission quantum yield. Most notably, this convenient synthetic approach reduces the need to perform the often challenging isolation of tris-heteroleptic complexes to a single divergent intermediate, which will simplify access to families of complexes of the form Ir(La)(Lb)(acac).

First-principles investigation on adsorption of anchors on two-dimensional halide perovskite material

Anchoring groups are important to immobilize the organic species on emerging energy materials such as the halide perovskite material surfaces to tailor their optoelectronic performance. In this manuscript, we employ first-principles calculations to closely examine the interfacial atomic structures, electronic and optical properties of the anchor/perovskite system, using Cs2PbBr4 as an example. 13 small molecular anchors with various functional anchoring groups, including halogen species (-F, -Cl, -Br and –I) and Lewis acids/bases (–COOH, –NH2, –NO2, –OH, -SH and thiophene) are investigated to comprehensively understand the fundamental interactions between the anchors and the two-dimensional halide perovskite surface. The hydrogen bonds play predominant role in the anchor/perovskite interfacial structural stabilization, while the halogen bonds are suggested to initiate weak interactions. These anchoring groups initiate disparate charge transfer characters at the halide perovskite surface, and the nitrobenzene anchor containing the –NO2 group presents perovskite → molecule surface charge transfer direction while most other anchors cause charge transfer in the reverse direction. In addition, the adsorption of the anchors causes blue-shifts in the UV–vis absorption spectra and optical bleaching effects in the resulting halide perovskite systems. The present study facilitates the fundamental understanding on the basic interactions between the anchoring species and the halide perovskite materials toward the photovoltaic applications.

Ultrapure Blue Thermally Activated Delayed Fluorescence (TADF) Emitters Based on Rigid Sulfur/Oxygen-Bridged Triarylboron Acceptor: MR TADF and D-A TADF.

Organic light-emitting diodes (OLEDs) still face a significant challenge in finding blue thermally activated delayed fluorescence (TADF) emitters that can achieve narrowband emission and high efficiency. In this work, we successfully design and synthesize a novel kind of TADF emitters based on rigid sulfur/oxygen-bridged triarylboron acceptor for ultrapure blue with narrowband electroluminescence. Time-dependent density functional theory (TD-DFT) calculations and photophysical results indicate the different intramolecular charge-transfer (ICT) character of two emitters. Benefiting from the rigid aromatic framework, both emitters exhibited deep-blue emission at 444 and 447 nm with a small full-width at half-maximum (fwhm) of about 33 nm, and a small singlet (S1)-triplet (T1) energy gap (ΔEST) of 0.23 and 0.36 eV. Consequently, OLEDs based on PhCz-TOSBA and TPA-TOSBA exhibit deep blue electroluminescence at 456 nm with fwhm of about 55 nm, affording high external quantum efficiencies (EQEs) of 16.69% with CIE coordinates of (0.14, 0.15) and 16.65% with CIE coordinates of (0.14, 0.12), respectively. These findings show that PhCz-TOSBA and TPA-TOSBA are superior emitters in ultrapure blue TADF devices.

Ab initio investigation of substituent effects on the excited electronic states of flavylium cation analogues of anthocyanin pigments

Anthocyanins are particularly noteworthy natural plant pigments that are responsible for the red, purple and blue color of many fruits, vegetables and flowers. Dietary anthocyanins have potential health benefits, but their color loss due to pH-dependent chemistry limits widespread application as coloring agents in food and consumer products. The ability to predict the color of synthetic analogues of natural pigments is crucial to the rational development of new bioinspired dyes and pigments with tailored colors and properties with lower potential for environmental and health concerns than those of conventional synthetic pigments. In this work, we employ the ab initio second-order algebraic diagrammatic construction, ADC(2), level of theory to calculate the absorption spectra of 26 synthetic flavylium cation analogues of anthocyanins. In general, the theoretical absorption spectra compare favorably with the corresponding experimental absorption spectra in an aqueous solution. The excitation energies, the charge transfer character, and the oscillator strengths of the electronic transitions provide insight into the effects of the type and position of the substituents on the excited singlet and triplet states of these compounds. The results show that the theoretical framework employed constitutes a reliable tool for obtaining a deeper understanding of the properties of bioinspired synthetic analogues of anthocyanin pigments.

Thermochromic Phosphors Based on One‐Dimensional Ionic Copper‐Iodine Chains Showing Solid‐State Photoluminescence Efficiency Exceeding 99 %

Thermochromic phosphors are intriguing materials for realizing thermochromic behaviors of light-emitting diodes. Here a highly luminescent and stable thermochromic phosphor based on one-dimensional Cu 4 I 6 (4-dimethylamino-1-ethylpyridinium) 2 is reported. This unique ionic copper-iodine chain-based hybrid exhibits near-unity photoluminescence efficiency owing to through-space charge-transfer character of relevant electronic transitions. More importantly, an alternative mechanism of thermochromic phosphorescence was unraveled, supported by first principle simulation of concerted copper atom migration in the copper-iodine chain. Furthermore, we successfully fabricate a bright thermochromic light-emitting diode using this Cu 4 I 6 (4-dimethylamino-1-ethylpyridinium) 2 thermochromic phosphor. Our reported flexible ionic copper-iodine chain-based thermochromic luminescent material represents a new type of cost-effective functional phosphor.

Experimental and computational studies on transition metals interaction with Leucine and Isoleucine

In this study, we reported the leucine and isoleucine based metal complexes with Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II). The complexes were synthesized in an aqueous medium followed by characterization with various experimental techniques. Besides experimental investigation, the density functional theory (DFT) calculation is performed which confirms a square planar structure for the Co, Ni and Cu complexes whereas Zn, Cd and Hg complexes adopt the distorted tetrahedral structure. The stability of the complexes is ensured by some calculated thermodynamic parameters. In addition, the elemental and thermos-gravimetric study are also conducted. Metal chelating affects the frontier molecular orbital energies of the ligand and reduces the HOMO-LUMO gap. The complexes are more reactive than the parent ligand. The FT-IR, UV-Visible and NMR spectral analysis of the complexes are reported. The experimental FT-IR and the electronic absorption properties agree with the calculated values. The presence of the characteristic metal-ligand charge transfer and d-d transitions in the complexes is confirmed through photo-excitation study. The UV-Visible reflectance spectral analysis indicates good conducting behavior of the complexes. The differential scanning calorimetry (DSC) analysis shows that the complexes undergo endothermic phase transition. The magnetic moment value agrees with the paramagnetic behavior of Co, Ni and Cu complexes but diamagnetic behavior of Zn, Cd and Hg complexes.

Phosphorescent Tris-cyclometalated Pt(IV) Complexes with Mesoionic N-Heterocyclic Carbene and 2-Arylpyridine Ligands.

The synthesis, structure, photophysical properties, and electrochemistry of the first series of Pt(IV) tris-chelates bearing cyclometalated aryl-NHC ligands are reported. The complexes have the general formula [Pt(trz)2(C∧N)]+, combining two units of the cyclometalated, mesoionic aryl-NHC ligand 4-butyl-3-methyl-1-phenyl-1H-1,2,3-triazol-5-ylidene (trz) with a cyclometalated 2-arylpyridine [C∧N = 2-(2,4-difluorophenyl)pyridine (dfppy), 2-phenylpyridine (ppy), 2-(p-tolyl)pyridine (tpy), 2-(2-thienyl)pyridine (thpy), 2-(9,9-dimethylfluoren-2-yl)pyridine (flpy)], and presenting a mer arrangement or metalated aryls. They exhibit a significant photostability under UV irradiation and long-lived phosphorescence in the blue to yellow color range, arising from 3LC excited states involving the C∧N ligands, with quantum yields of up to 0.34 in fluid solution and 0.77 in the rigid matrix at 298 K. The time-dependent density functional theory (TD-DFT) calculations reveal that nonemissive, deactivating excited states of ligand-to-metal charge-transfer (LMCT) character are pushed to high energies as a consequence of the strong σ-donating ability of the carbenic moieties, making the Pt(trz)2 subunit an essential structural component that enables efficient emissions from the chromophoric C∧N ligands, with potential application for the development of different Pt(IV) emitters with tunable properties.

Fluorescent phenothiazine-triazine donor-acceptor conjugates by facile consecutive nucleophilic displacement – Color tuning by substitution and protochromicity

A series of phenothiazine-triazine chromophores is prepared starting from brominated phenothiazine in a one-pot fashion by twofold nucleophilic substitution on cyanuric chloride. The title compounds show high fluorescence quantum yields in solution and in the solid state spanning a color range from deep blue to red by modulating the acceptor strength of the triazine moiety. Electron deficient substituted triazine chromophores exhibit a strong charge transfer character as shown by solvatochromism studies and small singlet-triplet energy gap making them interesting-candidates for thermally activated delayed fluorescence (TADF). Protonation of an electron rich triazine chromophore resulted in shifted spectral emission and showed in one case the formation of complementary emission colors and white light formation. Thus, by substitution of the triazine spectral emission color can be fine-tuned and specific photophysical properties like TADF and white light emission can be addressed.

Nonaromatic amine containing Dibenzo[b,d]thiophene donor for D-A type visible-light-driven fluorescence turn-on diarylethenes

Fluorescence turn-on diarylethenes (DAEs) are promising photoswitches for super-resolution bioimaging. However, all visible-light-driven photoswitchable DAEs are still rare. Here we report three D-A type visible-light-triggered fluorescence turn-on DAEs 1–3 by employing dibenzo[b,d]thiophene (DBTP) donor and 2,3-bis(2-methyl-1-benzothiophene-1,1-dioxide-3-yl)-thiophene (BTTO4) acceptor. It is found that the introduction of DBTP extends the molecular π-conjugation and increases the intramolecular charge-transfer character of BTTO4, which enables 1–3 open-isomers visible-light-triggered cyclization as well as turn-on fluorescence with a lifetime of 2.15–2.42 ns and relatively high PLQYs (0.18–0.21). All molecules show thermal stability, fatigue resistance, and photostability. Particularly, less than 20% degradation was observed for 1(c) and 2(c) after prolonged 405 nm light irradiation for 200 min. As a strong electron-donating group, DBTP offers new choices for the design of visible-light-driven fluorescence turn-on DAEs.