"A photo-induced colorimetric reaction of N, N'-bis[2-(trimethylammonium)ethyl]-1,8:4,5-naphthalenetetracarboxdiimide for detection of carboxylate anions ",
Tetrahedron Letters, 100 , 153860 (2022).
Here we show a novel colorimetric sensor system with a photo-induced colorimetric reaction of N,N'-bis[2-(trimethylammonium)ethyl]-1,8:4,5-naphthalenetetracarboxdiimide (TENDI) to detect and quantify carboxylate derivatives. In the presence of CH3COONa, TENDI aqueous solution under UV irradiation shows a photo-induced colorimetric reaction, which is due to the production of naphthalenediimide (NDI)-based radical anions whose absorbance peaks appear at around 400-600 nm. In contrast, no color changes are observed in the cases of diverse inorganic salts. In addition, TENDI shows another ability to discriminate the structural features of carboxylate derivatives by color tone. Moreover, interestingly, the Hill equation can approximate the relationship between carboxylate concentrations and absorbance values on the maximum absorbance wavelengths of the absorbance peaks due to the NDI-radical anions.
"Unique Photophysical Properties of 1,8-Naphthalimide Derivatives: Generation of Semi-stable Radical Anion Species by Photo-Induced Electron Transfer from a Carboxy Group ",
ACS Omega, 6 , 13456-13465 (2021).
(Back cover) (Open access)
The development of anion sensors for selective detection of a specific anion is a crucial research topic. We previously reported a selective photo-induced colorimetric reaction of 1-methyl-3-(N-(1,8-naphthalimidyl)ethyl) imidazolium (MNEI) having a cationic receptor in the presence of molecules having multiple carboxy groups, such as succinate, citrate, and polyacrylate. However, the mechanism underlying this reaction was not clarified. Here, we investigate the photo-induced colorimetric reaction of N-[2-(trimethylammonium)ethyl]-1,8-naphthalimide (TENI), which has a different cationic receptor from MNEI and undergoes the photo-induced colorimetric reaction, and its analogues to clarify the reaction mechanism. The TENI analogues having substituents on the naphthalene ring provide important evidence, suggesting that the colorimetric chemical species were radical anions generated via photo-induced electron transfer from carboxylate to the naphthalimide derivative. The generation of the naphthalimide-based radical anion is verified by 1H NMR and cyclic voltammetry analyses, and photo-reduction of methylene blue is mediated by TENI. In addition, the role of the cationic receptor for the photo-induced colorimetric reaction is investigated with TENI analogues having different hydrophilic groups instead of the trimethylammonium group. Interestingly, the photo-induced colorimetric reaction is observed in a nonionic analogue having a polyethylene glycol group, indicating that the colorimetric reaction does not require a cationic receptor. On the other hand, we reveal that the trimethylammonium group stabilizes the radical anion species. These generation and stabilization phenomena of naphthalimide-based radical anion species will contribute to the development of sophisticated detection systems specific for carboxylate.
"Theoretical study on photo-induced processes of 1-methyl-3-(N-(1,8-naphthalimidyl)ethyl)imidazolium halide species: an application of constrained density functional theory ",
Physical Chemistry Chemical Physics, 20 , 3911-3917 (2018).
(Back cover)
1-Methyl-3-(N-(1,8-naphthalimidyl)ethyl)imidazolium (MNEI) has potential as a versatile sensor that can measure the electronegativity of anions based on the fluorescence intensity upon irradiation. To clarify the factors that determine the fluorescence intensity, constrained density functional theory (CDFT) was applied to explore the electron transfer (ET) states of MNEI halide species (MNEI-X; X = F, Cl, Br, I). According to the CDFT potential energy surface, intra-molecular ET (SM1) states on MNEI are responsible for the intensity of absorption and fluorescence spectra. However, inter-molecular ET (SET) states between MNEI and X are certainly responsible for fluorescence quenching. Hence, the energetic difference between the SM1 state and the SET state (ΔEM1_ET) is a crucial factor that determines the fluorescence intensity in the spectra of MNEI-X complexes. ΔEM1_ET decreases as the electronegativity of X decreases (i.e., F > Cl > Br > I). This explains the fluorescence intensity of MNEI-X.
"Intermolecular electron transfer states of 1-methyl-3-(N- (1,8-naphthalimidyl)ethyl)imidazolium iodide obtained by constrained density functional theory",
Physical Chemistry Chemical Physics, 18 , 17795-17798 (2016).
(Back cover)
Electron transfer (ET) states of 1-methyl-3-(N-(1,8-naphthalimidyl)ethyl)imidazolium iodide are responsible for its photophysics. Investigation of an ET state based on constrained density functional theory (CDFT) revealed that nonradiative decay from the ET excited state is mediated by the interaction of the iodine atom with the 1,8-naphthalimide or the imidazolium group.
"A novel 1,8-naphthalimide derivative with an open space for an anion: unique fluorescence behaviour depending on the binding anion's electrophilic properties",
Chem. Commun. , 51 , 8596-8599 (2015).
(Back cover)
We have designed a novel 1,8-naphthalimide derivative with an open space for an anion. Computational calculation has predicted that the space could trap various anion species and photo-induced charge transfer depending on the anion's electrophilic properties. Indeed, the fluorescence behaviour of the 1,8-naphthalimide derivative complexes with each anion is consistent with the computational prediction.
"Theoretical Study of Singlet Oxygen Molecule Generation via an Exciplex with Valence-Excited Thiophene",
J. Phys. Chem. A, 119 , 876-883 (2015).
Singlet-oxygen [O2 (1Δg)] generation by valence-excited thiophene (TPH) has been investigated using multireference Møller-Plesset second-order perturbation (MRMP2) theory of geometries optimized at the complete active space self-consistent field (CASSCF) theory level. Our results indicate that triplet TPH (13B2) is produced via photo-induced singlet TPH (21A1) because 21A1 TPH shows a large spin-orbit coupling constant with the first triplet excited state (13B2). The relaxed TPH in the 13B2 state can form an exciplex with O2 (3Σg-) because this exciplex is energetically more stable than the relaxed TPH. The formation of the TPH (13B2) exciplex with O2 (3Σg-) whose total spin multiplicity is triplet (T1 state) increases the likelihood of transition from the T1 state to the singlet ground or first excited singlet state. After the transition, O2 (1Δg) is emitted easily although the favorable product is that from a 2+4 cycloaddition reaction.
"Computational study on photo- and thermo-reactions between tetra-tert-butyl-substituted cyclobutadiene and tetrahedrane",
Comput. Theoret. Chem., 969 , 44-52 (2011).
We have investigated the photo-chemical reaction from tetra-tert-butylcyclobutadiene (TB-CBD) to tetra-tert-butyltetrahedrane (TB-THD) and its reverse thermo-chemical reaction processes in the ground state by using CASSCF and MRMP2 computational methods. According to our results, the initial step of the photochemical reaction is the HOMO-LUMO single-electron excitation (11B1 state) and the arrangement from TB-CBD to TB-THD occurs via the HOMO-LUMO double electron excited state (21A1 state). After the transition from the 11B1 to the 21A1 state, most TB-CBD molecules show only photo-physical property without any reactions because the final point of the minimum-energy-path (MEP) calculation at the MRMP2//CASSCF level is the S1/S0 conical intersection (ionic like structure), which results in turning back to TB-CBD in the S0 state. However, on the way to the final point of the MEP, it is possible for some TB-CBD to transit at another S1/S0 conical intersection (tetra radical like structure), which is related to the photoreaction from TB-CBD to TB-THD. On the other hand, two routes from TB-THD to TB-CBD were found in the S0 state. One is the route via bicyclodiradical transition state. The other is the ionic transition state. In both reaction paths, only one TS is there in contrast to the plural step reaction suggested previously.
"Ground State Potential Energy Surface between Cyclobutadiene and Tetrahedrane Looked Down from S1/S0 Conical Intersections",
Tetrahedron, 66 (28), 5212-5217 (2010).
We have explored the singlet ground state potential energy surface (S0 PES) between cyclobutadiene (CBD) and tetrahedrane (THD) looked down from S1/S0 conical intersections through multi-configuration self-consistent field theory. On the basis of the obtained S0 PES, we propose the revised process of the THD to CBD symmetry-forbidden reaction. According to the present result, the THD to CBD rearrangement occurs via plural steps similarly to previous suggestions, but via a tetra-radical species (instead of an endo-species), which is considered for the first time in this paper. Since the endo-species is significantly destabilized when hydrogen atoms are replaced by bulky substituents (such as tert-butyl group), the present one, where endo-species are not involved, would be realized in actual systems having bulky substituents.
"Tetra-radical and Ionic S1/S0 Conical Intersections of Cyclobutadiene",
Chem. Phys., 371 (1), 30-35 (2010).
We have located two conical intersections between the first singlet excited (S1) and singlet ground (S0) states of cyclobutadiene (CBD) using the complete active space self-consistent field (CASSCF) method. One is the ionic-structure S1/S0 conical intersection (CIionic), which was located by carrying out a minimum-energy-path calculation from the Franck-Condon point of the HOMO to LUMO double-electron excited state, and the other is the tetra-radical S1/S0 conical intersection (CItetra), which was located by exploring the S1/S0 degeneracy space. While CIionic is only involved in the automerization of CBD, CItetra is involved in not only the automerization but also the criss-cross reaction. It is possible for one of the highest constrained compounds, tetrahedrane, to be produced if S1 excited CBD undergoes a transition to the S0 state via the tetra-radical S1/S0 conical intersection. In this paper, we discuss the possibility that unsubstituted tetrahedrane can be produced by irradiating CBD.
"Acceleration of the Z to E Photoisomerization of Penta-2,4-dieniminium by Hydrogen Out-of-Plane Motion: Theoretical Study on a Model System of Retinal Protonated Schiff Base",
Phys. Chem. Chem. Phys., 11, 6406-6414 (2009).
We report the result of comparison between two reaction coordinates [on the potential energy surface of the first excited state (S1)] produced by CASSCF and these energies recalculated by MRMP2 in the Z to E photoisomerization of penta-2,4-dieniminium (PDI) as the minimal model of the retinal protonated Schiff base (RPSB). One coordinate is the S1 state minimum-energy-path (MEP) in mass-weighted coordinates from the S1 vertically excited point, where a strong hydrogen-out-of plane (HOOP) motion is not exhibited. The energy profile of the S1 MEP at the MRMP2//CASSCF level shows a barrier for the rotation around the reactive C-C and hits the S1/S0 degeneracy space where the central C-C-C-C dihedral angle is distorted by 65 degrees. The other coordinate is an S1 coordinate obtained by the relaxed scan strategy. The relaxed coordinate along the central C-C-C-C dihedral angle, which we call the HOOP coordinate, shows strong HOOP motion. According to the MRMP2//CASSCF calculation, there is no barrier on the HOOP coordinate. Furthermore, the S1 to S0 transition may be possible without the large skeletal deformation by HOOP motion because the HOOP coordinate encounters the S1/S0 degeneracy space where the central C-C-C-C dihedral angle is distorted by only 40 degrees. Consequently, if PDI is a suitable model molecule for the RPSB as often assumed, the 11-cis to all-trans photoisomerization is predicted to be accelerated by the HOOP motion.
"Revisiting the S1/S0 Degeneracy Space along the Exocyclic Methylene Twist Motion of Fulvene through Two-Step Procedure",
J. Chem. Theor. Comp., 4 (1), 42-48 (2008).
We have characterized the degeneracy space (DS) between the ground (S0) state and the first excited (S1) state along the exocyclic methylene twist motion of fulvene, using our calculation strategy, i.e., a two-step procedure with CASSCF. The origin of the "cancellation error" on locating degeneracy points under geometrical constraints is analyzed, leading to a method to assess adequacy of the strategy. According to our estimation, these S1/S0 DPs are optimized for energy within 2.0 10-3 Eh Angstrom-1 (the value of root-mean-square). From the obtained S1/S0 DS, we provide some information about the exocyclic methylene rotation by 180 degrees.
"Ab initio Study on One-Way Photoisomerization of Maleic Acid and Fumaric Acid Anion Radical System as a Model System of Their Esters",
J. Phys. Chem. A, 110 (44), 12276-12281 (2006).
Potential energy surfaces (PESs) of the maleic acid anion radical (MA−•: cis isomer)/fumaric acid anion radical (FA−•: trans isomer) system as a model system of their esters have been studied in detail using CASSCF method.
The results suggest the following: The photoisomerization is initiated with the H-C-C-H dihedral angle distortion [hydrogen out of plain (HOOP) motion] on the D1 PES.
The C-C-C-C dihedral angle distortion occurs on the D0 PES after the deactivation from D1 to D0.
A large fraction of the net motion along the isomerization coordinate occurs on the D
"Theoretical Study on Hula-Twist Motion of Penta-2,4- Dieniminium on the S1 Surface under Isolated Condition by the Complete Active Space Self-Consistent Field Theory",
Chem. Phys. Lett., 424 (4-6), 374-378 (2006).
Hula-twist (HT) motion of Z-penta-2,4-dieniminium (PDI) on the S1 surface is studied on the basis of complete active space selfconsistent field (CASSCF) theory. An S1/S0 crossing region (a segment of the S1/S0 conical intersection hyperline) along a HT coordinate (simultaneous rotation of the central double bond and an adjacent single bond) is characterized. One-dimensional relaxed scan calculation along the postulated HT coordinate shows no barrier up to the S1/S0 crossing region, suggesting the possible involvement of the HT process in a fast photochemical reaction in constrained states.
"A note on geometric constraints in conical intersection optimizations",
J. Mol. Struct. (Theochem), 731 (1-3), 173-175 (2005).
Geometric constraints (i.e. fixing one or more of bond distances, bond angles, or dihedral angles) are not compatible with conical intersection (CI) optimizations by the projected gradient method. However, a two-step procedure can be efficiently used for approximate relaxed scans (i.e. with geometry optimization at each point) of hyperlines formed by continuously connected CIs.
"Characterization of the hyperline of D1/D0 conical intersections between the maleic acid and fumaric acid anion radicals",
J. Chem. Phys., 121 (14), 7030-7031 (2004).
The cation and anion radicals of symmetrical 1,2-disubstituted ethylenes are expected to have a symmetry-allowed conical intersection (CI) between the ground doublet state (D0) and the lowest excited doublet state (D1) near a 90 degrees-twisted geometry. By the complete active space self-consistent field method, we characterized the hyperline formed by D1/D0 CIs between the anion radicals of maleic acid (cis) and fumaric acid (trans). An implication of the results for the known one-way cis to trans photoisomerization of the maleic acid anion radical and other related ion radicals is presented.