Advancing Molecular-Scale Logic Devices through Multistage Switching in a Luminescent Bimetallic Ru(II)-Terpyridine Complex

Stimuli-responsive multistep switching phenomena of a luminescent bimetallic Ru(II) complex are employed herein to fabricate multiple configurable logic devices. The complex exhibits "off-on" and "on-off" emission switching upon alternative treatment with visible and UV light. Additionally, remarkable augmentation of the rate as well as quantum yield of photoisomerization was achieved via the use of a chemical oxidant (Ce4+) as well as a reductant (metallic sodium). Upon exploiting the emission spectral response of the complex, several advanced Boolean logic functions, including IMPLICATION as well as 2-input 2-output and 3-input 2-output complex combinational logic gates, are successfully implemented. Additionally, by utilizing the vast efficacy of Python, a novel "logic_circuit" model is devised that is capable of making accurate decisions under the influence of various input combinations. This model transcends traditional Boolean logic gates, offering flexibility and intuition to design logical functions tailored to specific chemical contexts. By integrating principles of logic circuits with chemical processes, this innovative approach enables structure determination of the chemical states based on input conditions, thereby unlocking avenues for exploring intricate interactions and reactions beyond conventional Boolean logic paradigms.

Control of Photoisomerization Kinetics via Multistage Switching in Bimetallic Ru(II)-Terpyridine Complexes

In this study, we carried out detailed experimental and theoretical investigation on photophysical, electrochemical, and photoisomerization behaviors of a new array of luminescent binuclear Ru(II) complexes derived from a phenylene-vinylene-substituted terpyridyl ligand possessing RT lifetimes within 60.3-410.5 ns. The complexes experienced trans-to-cis isomerization in MeCN on irradiation with visible light, accompanied by significant changes in their absorption and emission spectral profiles. The reverse cis-to-trans process is also possible with the use of ultraviolet (UV) light. On conversion from trans to cis isomers, the emission intensity increases substantially, while for the reverse process, luminescence quenching occurs. Thus, "off-on" and "on-off" emission switching is facilitated upon treatment with visible and UV light alternatively. By the use of chemical oxidants (ceric ammonium nitrate and potassium permanganate) and reductants (metallic sodium) as well as light of appropriate wavelengths, multistate switching phenomena involving reversible oxidation-reduction and trans-cis isomerization have been achieved. Interestingly, the rate of this multistate photoswitching process becomes much faster compared to only two-state trans-cis isomerization of these complexes. Density functional theory (DFT) and time-dependent-DFT (TD-DFT) calculations are also performed to obtain a clear picture of the electronic environment of the complexes and also for the appropriate assignment of absorption and emission spectral bands.

Insights into the Effect of Trans-to-Cis Photoisomerization of a Co-coordinated Stilbene Derivative on the Luminescence of Di-β-diketonate Lanthanide Complexes

Five lanthanide complexes constructed from a stilbene derivative, (E)-N',N'-bis(pyridin-2-ylmethyl)-4-styrylbenzoyl hydrazide (HL), and two β-diketonates (2-thenoyltrifluoroacetonate, tta), with or without a trifluoroacetate anion (CF₃CO₂ ^-), namely, [Ln(tta)₂(HL) (CF₃CO₂)] [LnC₄₅H₃₂F₉N₄O₇S₂, Ln = La (1), Nd (2), Eu (3), or Gd (4)] and [Yb(tta)₂(L)] (YbC₄₃H₃₁F₆N₄O₅S₂ (5), L = deprotonated HL), were synthesized and characterized. Crystals of these five complexes were obtained and analyzed by single-crystal X-ray diffraction. These complexes all belonged to the monoclinic P2₁/c space group. For La³⁺, Nd³⁺, Eu³⁺, and Gd³⁺, the central lanthanide ion was nine-coordinate with a monocapped twisted square antiprism polyhedron geometry. The central Yb³⁺ ion of complex 5 was eight-coordinate with a distorted double-capped triangular prism polyhedron geometry. Among the five complexes, trans-to-cis photoisomerization of the stilbene group in gadolinium complex 4 showed the largest quantum yield. Complexes 2, 3, and 4 showed dual luminescence and photoisomerization functions. The luminescence change of complex 3 was reversible upon the trans-to-cis photoisomerization process. The sensitization efficiencies of luminescent europium complex 3 in acetonitrile solutions and in the solid state were 49.9 and 42.6%, respectively. These medium sensitization efficiencies led to the observation of simultaneous photoisomerization and luminescence, which further confirmed our previous report that photoisomerization of the stilbene group within complexes was related to the lanthanide ion energy level and whether a ligand-to-metal center or ligand-to-ligand charge-transfer process was present. In complexes 1-5, in addition to the intramolecular absorption transition of the ligand itself (IL, π_HL-π_HL ^* and π_tta-π_tta*), the presence of a ligand-to-ligand charge-transfer transition between tta and HL (LLCT, π_tta-π_HL ^* or π_HL-π_tta ^*) indicated whether the triplet-state energy of HL was able to transfer to the excited energy level of the lanthanide ions, leading to different extents of HL photoisomerization. These results provide an important route for the design of new dual-function lanthanide-based optical switching materials.

Accessible triplet excited states in the photoisomerization of allenes with extended conjugation

A series of bidentate allene- and enyne-containing ligands have been synthesized and the photochemical properties of their rhenium(I) complexes have been studied. These complexes exhibit facile isomerization of the conjugated double bonds upon ambient light exposure. Simulations unveiled a very efficient intersystem crossing and the consequent key role of the triplet states in the observed photochemistry of these substrates upon rhenium(I) complexation.

Accessing the triplet manifold of naphthalene benzimidazole-phenanthroline in rhenium(I) bichromophores

The steady-state and ultrafast to supra-nanosecond excited state dynamics of fac-[Re(NBI-phen)(CO)₃(L)](PF₆) (NBI-phen = 16H-benzo[4',5']isoquinolino[2',1':1,2]imidazo[4,5-f][1,10]phenanthrolin-16-one) as well as their respective models of the general molecular formula [Re(phen)(CO)₃(L)](PF₆) (L = PPh₃ and CH₃CN) has been investigated using transient absorption and time-gated photoluminescence spectroscopy. The NBI-phen containing molecules exhibited enhanced visible light absorption with respect to their models and a rapid formation (<6 ns) of the triplet ligand-centred (LC) excited state of the organic ligand, NBI-phen. These triplet states exhibit an extended excited state lifetime that enable the energized molecules to readily engage in triplet-triplet annihilation photochemistry.

Emission Switching in the Near-Infrared by Reversible Trans-Cis Photoisomerization of Styrylbenzene-Conjugated Osmium Terpyridine Complexes

A new array of homoleptic osmium(II) complexes based on styrylbenzene-conjugated terpyridine ligands (tpy-pvp-X) were synthesized and their photophysical, electrochemical, and photoisomerization behaviors thoroughly investigated in this work. Both electron-donating and -withdrawing substituents were incorporated onto a tpy-pvp-X (X = H, Me, Cl, NO₂, and Ph) moiety to tune the optical properties and also the rate of photoisomerization behaviors in the complexes. All complexes display strong spin-allowed singlet metal-to-ligand charge-transfer bands in the visible (495-506 nm) and weak singlet ground state to triplet metal-to-ligand charge-transfer (³MLCT) broad bands within the 600-700 nm range. The complexes also exhibit strong phosphorescence emission from their ³MLCT state in the near-infrared domain (737-752 nm) at room temperature with excited-state lifetimes spanning between 107 and 165 ns. Two styrylbenzene units promote reversible trans-trans to trans-cis/cis-cis isomerization induced by light. The rate constants and quantum yields of photoisomerization were found to vary linearly with the Hammett σ_p parameters of the substituents. The rate and quantum yields were also found to decrease with increasing polarity of the solvents. Considerable modulation of the optical behavior along with luminescence switching in the complexes has been achieved upon photoisomerization. Moreover, the optical outputs as a function of two photonic stimuli inputs were used to demonstrate the binary function of a two-input IMPLICATION logic gate. In conjunction with the experimental study, computational investigations were also carried out in all three conformations of the complexes (trans-trans, trans-cis, and cis-cis) to have a perception of their electronic structures and for correct assignment of their absorption and emission spectral bands.

Spectroscopic Study of the E/Z Photoisomerization of a New Cyrhetrenyl Acylhydrazone: A Potential Photoswitch and Photosensitizer†

The new cyrhetrenyl acylhydrazone [(CO)₃ Re(η⁵ -C₅ H₄ )-C(O)-NH-N = C(CH₃ )-(2-C₄ H₂ S-5-NO₂ )] (E-CyAH) has been designed, synthesized and fully characterized to study the effect of having a cyrhetrenyl fragment (sensitizer) covalently bonded to an acylhydrazone moiety (switch), on its photophysical and photochemical properties. The crystal structure reveals that E-CyAH adopts an E-configuration around the iminic moiety [-N = C(CH₃ )]. The absorption spectrum of E-CyAH displays two bands at 270 and 380 nm, which are mainly ascribed to π → π* intraligand (IL) and d_π  → π* metal-to-ligand charge transfer (MLCT) transitions, being consistent with DFT/TD-DFT calculations. Upon 365 nm irradiation, E-CyAH photoisomerizes to Z-CyAH, as evidenced by UV-Vis and ¹ H-NMR spectral changes, with a quantum yield value Φ_{E -CyAH → Z -CyAH} of 0.30. Z-CyAH undergoes a first-order thermal back-isomerization process, with a relatively short half-life τ_1/2 of 277 min. Consequently, E-CyAH was quantitatively recovered after 24 h, making it a fully reversible T-type molecular photoswitch. This remarkable behavior allows us to measure the individual photophysical properties for both isomers. In addition, E-CyAH and Z-CyAH efficiently photosensitize the generation of singlet oxygen (O₂ (¹ Δ_g )) with good yield (Φ_Δ  = 0.342).

Excited-State Triplet Equilibria in a Series of Re(I)-Naphthalimide Bichromophores

We present the synthesis, structural characterization, electronic structure calculations, and the ultrafast and supra-nanosecond photophysical properties of a series of five bichromophores of the general structural formula [Re(5-R-phen)(CO)₃(dmap)](PF₆), where R is a naphthalimide (NI), phen = 1,10-phenanthroline, and dmap is 4-dimethylaminopyridine. The NI chromophores were systematically modified at their 4-positions with -H (NI), -Br (BrNI), phenoxy (PONI), thiobenzene (PSNI), and piperidine (PNI), rendering a series of metal-organic bichromophores (Re1-Re5, respectively) featuring variability in the singlet and triplet energies in the pendant NI subunit. Five closely related organic chromophores as well as [Re(phen)(CO)₃(dmap)](PF₆) (Re6) were investigated in parallel to appropriately model the photophysical properties exhibited in the bichromophores. The excited state processes of all molecules in this study were elucidated using a combination of transient absorption spectroscopy and time-resolved photoluminescence (PL) spectroscopy, revealing the kinetics of the energy transfer processes occurring between the appended chromophores. The spectroscopic analysis was further supported by electronic structure calculations which identified the origin of many of the experimentally observed electronic transitions.

Thermally Induced trans-to-cis Isomerization and Its Photoinduced Reversal Monitored using Absorption and Luminescence: Cooperative Effect of Metal Coordination and Steric Substituent

For ethene derivatives with large groups the cis-isomer is often quite unstable and unavailable. Herein, we report an exception of two stable coordination complexes, (cis-L)ZnCl₂ , starting from trans-1,2-bis(1-R-benzo[d]imidazol-2-yl)ethene (R=H, L1; R=CH₃ , L2) ligands under solvothermal condition (T ≥140 °C). Using the intensity of the absorption and luminescence spectra as probes we proposed its progressive cis-to-trans reversal upon irradiation with UV light, which was confirmed by powder X-ray diffraction (PXRD). Similar results observed in the series of (cis-L2)M^II Cl₂ [M=Fe (4), Co (5), Ni (6)] demonstrate the universal strategy. The results of PXRD, NMR spectroscopy, ESI-MS and DFT calculations support the above conclusion. NMR spectroscopy indicates that irradiation of 1 converts an optimized 71 % of the cis-isomer to trans, whereas the free trans-L1 ligand transforms to only 15 % cis-isomer under similar conditions.

Molecular engineered rhenium(i) carbonyl complexes to promote photoisomerization of coordinated stilbene-like ligands in the visible region

Novel fac-[Re(CO)₃(dmcb)(trans-stpyR)]⁺ complexes have been judiciously engineered to absorb at lower energies and sensitize trans-4-styrylpyridine (trans-stpy) or trans-4-(4-cyano)styrylpyridine (trans-stpyCN) photoisomerizable ligands up to 436 nm of irradiation.

Photoisomerization of di-nuclear rhenium(i) bpe-based compounds

Photoisomerization processes of [{(NN)(CO)₃Re}₂(trans-bpe)]²⁺ complexes showed the contribution of the singlet pathway in addition to the usually observed triplet one. The luminescence observed for the cis-complexes in CH₃CN is able to efficiently photosensitize the generation of ¹O₂.