Efficient photochromic transformation of a new fluorenyl diarylethene: one- and two-photon absorption spectroscopy

Nondestructive All-Optical Readout through Photoswitching of Intramolecular Excimer Emission

We report the first intramolecular excimer photoswitching induced by molecular motion within a dithienylethene (DTE) molecule without destructive readout. The photochromic compound DTE bears two pyrene chromophores, judiciously positioned to face each other in the DTE's open form. The close proximity of the pyrenes in the open form is confirmed by NMR experiments and geometry optimization. Intense pyrene excimer luminescence is recorded, upon both one- and two-photon excitation (OPE and TPE). The photocyclization reaction of the DTE core induces a molecular motion of one pyrene moiety which thus prevents the possibility of formation of an excimer. Our DTE-based pyrene is stable upon TPE irradiation and shows a high photocyclization quantum yield. Such property specifications allow us to report the original nondestructive readout fluorescence by alternating exposure to OPE and TPE.

Toward Two-Photon Absorbing Dyes with Unusually Potentiated Nonlinear Fluorescence Response

The combination of two two-photon-induced processes in a Förster resonance energy transfer (FRET)-operated photochromic fluorene-dithienylethene dyad lays the foundation for the observation of a quartic dependence of the fluorescence signal on the excitation light intensity. While this photophysical behavior is predicted for a four-photon absorbing dye, the herein proposed approach opens the way to use two-photon absorbing dyes, reaching the same performance. Hence, the spatial resolution limit, being a critical parameter for applications in fluorescence imaging or data storage with common two-photon absorbing dyes, is dramatically improved.

Synthesis and properties of a photochromic perinaphthothioindigo conjugated with two porphyrins

In this study, we synthesized a new porphyrin-perinaphthothioindigo composite in which two porphyrins are connected to a perinaphthothioindigo dye through ethynyl linkages. The UV-vis absorption spectra of the composite showed an absorption peak originating from the trans-isomer at around 730 nm. Upon photoirradiation at 760 nm, the intensity of this absorption decreased with increasing absorption of the cis-isomer around 500 nm. The HOMO–LUMO absorption of the cis-isomer is blue-shifted by ˜230 nm compared to that of trans-isomer due to lack of [Formula: see text] conjugation. The shift by 230 nm is 100 nm larger than that observed for the monoporphyrin-substituted compound, indicating the expansion of [Formula: see text] conjugation by the additional porphyrin.

Core structure dependence of cycloreversion dynamics in diarylethene analogs

Increased core rigidity in diarylethene-type photoswitches results in shallower excited-state potential energy surfaces and faster funneling towards the conical intersections from which cycloreversion and nonreactive deactivation occur.

Level of Theory and Solvent Effects on DASA Absorption Properties Prediction: Comparing TD-DFT, CASPT2 and NEVPT2

Donor-acceptor Stenhouse adducts (DASAs) are a very recent class of organic photoswitches that combine excellent properties, such as color and polarity change, a large structural modification, and excellent fatigue resistance. Despite their potential applications in different fields, very few studies have focused on rationalizing their electronic structure properties. Here, by means of different state-of-the-art theoretical methods, including solvent and vibrational effects, we show that while time dependent-density functional theory (TD-DFT) can qualitatively describe DASAs' excited states, multiconfigurational quantum chemistry methods along with dynamic electron correlation (CASPT2, NEVPT2) are required for a quantitative agreement with the experiment. This finding is reasoned based on the different charge transfer characteristics observed. Moreover, the TD-DFT computed two-photon absorption properties are reported and suggested to red-shift the absorption band, as required for biological applications.

Two-Photon Absorbing Phosphorescent Metalloporphyrins: Effects of π-Extension and Peripheral Substitution

The ability to form triplet excited states upon two-photon excitation is important for several applications of metalloporphyrins, including two-photon phosphorescence lifetime microscopy (2PLM) and two-photon photodynamic therapy (PDT). Here we analyzed one-photon (1P) and degenerate two-photon (2P) absorption properties of several phosphorescent Pt (II) porphyrins, focusing on the effects of aromatic π-extension and peripheral substitution on triplet emissivity and two-photon absorption (2PA). Our 2PA measurements for the first time made use of direct time-resolved detection of phosphorescence, having the ability to efficiently reject laser background through microsecond time gating. π-Extension of the porphyrin macrocycle by way of syn-fusion with two external aromatic fragments, such as in syn-dibenzo- (DBP) and syn-dinaphthoporphyrins (DNP), lowers the symmetry of the porphyrin skeleton. As a result, DBPs and DNPs exhibit stronger 2PA into the one-photon-allowed B (Soret) and Q states than fully symmetric (D4h) nonextended porphyrins. However, much more 2P-active states lie above the B state and cannot be accessed due to the interfering linear absorption. Alkoxycarbonyl groups (CO2R) in the benzo-rings dramatically enhance 2PA near the B state level. Time-dependent density functional theory (TDDFT) calculations in combinations with the sum-over-states (SOS) formalism revealed that the enhancement is due to the stabilization of higher-lying 2P-active states, which are dominated by the excitations involving orbitals extending onto the carbonyl groups. Furthermore, calculations predicted even stronger stabilization of the 2P-allowed gerade-states in symmetric Pt octaalkoxycarbonyl-tetrabenzoporphyrins. Experiments confirmed that the 2PA cross-section of PtTBP(CO2Bu)8 near 810 nm reaches above 500 GM in spite of its completely centrosymmetric structure. Combined with exceptionally bright phosphorescence (ϕphos = 0.45), strong 2PA makes Pt(II) complexes of π-extended porphyrins a valuable class of chromophores for 2P applications. Another important advantage of these porphyrinoids is their compact size and easily scalable synthesis.

A strategy to design novel structure photochromic sensitizers for dye-sensitized solar cells

Two sensitizers with novel structure were designed and synthetized by introducing photochromic bisthienylethene (BTE) group into the conjugated system. Thanks to the photochromic effect the sensitizers have under ultraviolet and visible light, the conjugated bridge can be restructured and the resulting two photoisomers showed different behaviors in photovoltaic devices. This opens up a new research way for the dye-sensitized solar cells (DSSCs).

Packing directed beneficial role of 3-D rigid alicyclic arms on the templated molecular aggregation problem

Tuning of solid state emission by controlling intermolecular interactions and spacing.

Density functional theory study of electric field effects on the isomerization of a photochromic molecular switch based on 1,2-dithienylethene

Structural and electronic properties of 1,2-bis(5-methyl-[2,2′-bithiophen]-4-yl)cyclopent-1-ene in closed form and open form under various external electric field with strengths, 0, 10 × 10−4, 20 × 10−4, 30 × 10−4, 40 × 10−4, and 50 × 10−4a.u., were studied using the DFT-B3LYP/6-31G* method. As a positive index, structural parameters, length of the photoisomers, and the electronic spatial extents are almost stable at different external electric fields. The UV-Vis electronic spectrum based on time-dependent density functional theory indicated that the HOMO → LUMO transition in the closed form under different electric field strengths is strongly allowed, whereas is very weak in the open form. Electronic response parameters such as the HOMO−LUMO gap, electric dipole moment, and polarizability showed that electric conductivity of the closed form at different field strengths is greater than in the open form. Results of electronic density of states show that at high external electric field, the conductivity of the open form and closed form will be probably equal and switching behavior cannot be observed. Isomerization of the closed form to the open form at different external electric fields can be considered as exothermic and spontaneous.

Photoisomerization-induced manipulation of single-electron tunneling for novel Si-based optical memory

We demonstrated optical manipulation of single-electron tunneling (SET) by photoisomerization of diarylethene molecules in a metal-insulator-semiconductor (MIS) structure. Stress is placed on the fact that device operation is realized in the practical device configuration of MIS structure and that it is not achieved in structures based on nanogap electrodes and scanning probe techniques. Namely, this is a basic memory device configuration that has the potential for large-scale integration. In our device, the threshold voltage of SET was clearly modulated as a reversible change in the molecular orbital induced by photoisomerization, indicating that diarylethene molecules worked as optically controllable quantum dots. These findings will allow the integration of photonic functionality into current Si-based memory devices, which is a unique feature of organic molecules that is unobtainable with inorganic materials. Our proposed device therefore has enormous potential for providing a breakthrough in Si technology.

Synthesis and photophysical properties of a porphyrin-perinaphthothioindigo dye

A new porphyrin-perinaphthothioindigo composite, where porphyrin and perinaphthothioindigo dye are connected though a triple bond, was synthesized. In UV-vis absorption spectra of the composite, absorption originating from the trans-isomer appeared at 655 nm. Upon photoirradiation at > 700 nm, the intensity of this absorption decreased with increase of absorption of the cis-isomer around at 530 nm. The HOMO–LUMO absorption of the cis-isomer is blue-shifted by 125 nm compared to that of trans-isomer due to the lack of π-conjugation. The 2PA cross-section values obtained for both isomers were 2,000 and 700 GM, respectively. The value of 2,000 GM is of the largest class among the values reported for photochromic compounds. The enhancement factors by the connection of porphyrin to perinaphthothioindigo were found to be 3.5–3.9 by measuring cross-section values of bis(TMS-ethynyl)perinaphthothioindigo as the reference compound. Two-photon isomerization of the trans-isomer to the cis-isomer was successfully conducted using femtosecond pulses.