Infrared-optical double-resonance measurements of hydrogen-bonding interactions in clusters involving aminophthalimides

Revised excited-state intramolecular proton transfer of the 3-Aminophthalimide molecule: A TDDFT study

The spectroscopic properties of 3-Aminophthalimide (3AP) molecule were investigated [Chem. Phys. 2002, 283, 249, New J. Chem. 2018, 42, 1181]. The result was that the 3AP molecule was exhibiting excited-state intramolecular proton transfer (ESIPT). In the research, we revised previous result using time-dependent density functional theory (TDDFT) method. The fluorescence spectrum shows that the only fluorescence peak is from initial enol form, which is different from the traditional case of ESIPT. The red shift of characteristic peaks in infrared vibration spectra is not induced by ESIPT process. The change in the vibration mode of the amino group causes the red shift of characteristic peak in the infrared spectrum. Energy curves indicate that the barrier (19.71 kcal/mol) is anomalously high in the first excited state. In addition, there are not stable points to lead the ESIPT to form a keto isomer. Together, these results demonstrate that there is not an ESIPT process happening of 3AP molecule.

Analytical Nuclear Excited-State Gradients for the Second-Order Approximate Coupled-Cluster Singles and Doubles (CC2) Method Employing Uncoupled Frozen-Density Embedding

We report the derivation and implementation of analytical orbital-relaxed properties and nuclear gradients for excited states using the second-order approximate coupled-cluster singles and doubles (CC2) model combined with uncoupled frozen-density embedding (FDEu). An implementation of the algebraic diagrammatic construction through second-order ADC(2), which arises from simplification of RICC2 FDEu, is also presented. In order to ensure a RICC2 FDEu Lagrange functional that is linear in the Lagrange multipliers, the Hartree-Fock density is employed for the target subsystem in the embedding contributions. The accuracy of the new scheme is assessed using the carbon monoxide molecule, 4-aminophthalimide, and a benzonitrile dimer, revealing that the obtained errors are below the method error of RICC2. Using density functional theory for the environment, the efficiency of the new method is illustrated by computing the perturbed excited-state dipole moment of a chromophore in a biological environment. For this system, comprising 32 molecules consisting of 366 atoms in total, the computation requires only a couple of days on a standard compute node. RICC2 FDEu thus enables large-scale calculations of ab initio wave functions for molecules in complex environments as routine applications.

The phenyl vinyl ether-methanol complex: a model system for quantum chemistry benchmarking

The structure of the isolated aggregate of phenyl vinyl ether and methanol is studied by combining a multi-spectroscopic approach and quantum-chemical calculations in order to investigate the delicate interplay of noncovalent interactions. The complementary results of vibrational and rotational spectroscopy applied in molecular beam experiments reveal the preference of a hydrogen bond of the methanol towards the ether oxygen (OH∙∙∙O) over the π-docking motifs via the phenyl and vinyl moieties, with an additional less populated OH∙∙∙P(phenyl)-bound isomer detected only by microwave spectroscopy. The correct prediction of the energetic order of the isomers using quantum-chemical calculations turns out to be challenging and succeeds with a sophisticated local coupled cluster method. The latter also yields a quantification as well as a visualization of London dispersion, which prove to be valuable tools for understanding the role of dispersion on the docking preferences. Beyond the structural analysis of the electronic ground state (S0), the electronically excited (S1) state is analyzed, in which a destabilization of the OH∙∙∙O structure compared to the S0 state is observed experimentally and theoretically.

Enhanced fluorescence of phthalimide compounds induced by the incorporation of electron-donating alicyclic amino groups

A significant difference in fluorescence properties between 3- and 4-substituted phthalimides demonstrates the formation of excited TICT and planar ICT states, respectively.

The Structure of Diphenyl Ether-Methanol in the Electronically Excited and Ionic Ground States: A Combined IR/UV Spectroscopic and Theoretical Study

Diphenyl ether offers competing docking sites for methanol: the ether oxygen acts as a common hydrogen-bond acceptor and the π system of each phenyl ring allows for OH-π interactions driven by electrostatic, induction, and dispersion forces. Based on investigations in the electronic ground state (S₀ ), we present a detailed study of the electronically excited state (S₁ ) and the ionic ground state (D₀ ), in which an impact on the structural preference is expected compared with the S₀ state. Dispersion forces in the electronically excited state were analyzed by comparing the computed binding energies at the coupled-cluster-singles (CCS) and approximate coupled-cluster-singles-doubles levels of theory (CC2 approximation). By applying UV/IR/UV spectroscopy, we found a more strongly bound OH-π structure in the S₁ state compared with the S₀ state, in agreement with spin-component-scaled CC2 calculations. A structural rearrangement into a non-hydrogen-bonded structure takes places upon ionization in the D₀ state, which was revealed by using IR photodissociation spectroscopy and confirmed by theory.

Analytical nuclear excited-state gradients for the Tamm-Dancoff approximation using uncoupled frozen-density embedding

We report the derivation and implementation of analytical nuclear gradients for excited states using time-dependent density functional theory using the Tamm-Dancoff approximation combined with uncoupled frozen-density embedding using density fitting. Explicit equations are presented and discussed. The implementation is able to treat singlet as well as triplet states and functionals using the local density approximation, the generalized gradient approximation, combinations with Hartree-Fock exchange (hybrids), and range-separated functionals such as CAM-B3LYP. The new method is benchmarked against supermolecule calculations in two case studies: The solvatochromic shift of the (vertical) fluorescence energy of 4-aminophthalimide on solvation, and the first local excitation of the benzonitrile dimer. Whereas for the 4-aminophthalimide-water complex deviations of about 0.2 eV are obtained to supermolecular calculations, for the benzonitrile dimer the maximum error for adiabatic excitation energies is below 0.01 eV due to a weak coupling of the subsystems. © 2017 Wiley Periodicals, Inc.

Multi-spectroscopic and theoretical analyses on the diphenyl ether–tert-butyl alcohol complex in the electronic ground and electronically excited state

Multi-spectroscopic and theoretical investigations on the isolated diphenyl ether–tert-butyl alcohol complex – an ideal benchmark system for theory with strongly competing OH–O and OH–π binding motifs.

Modulation of the 4-aminophthalimide spectral properties by hydrogen bonds in water

TD-DFT and DFT calculations have been performed to examine the relationship between the spectral shifts of 4-aminophthalimide (4AP) and the formation of hydrogen bonds in water solution. The computations of the S0 state are at the IEFPCM-B3LYP/6-311++G(d, p) level and the S1 state at the TD-IEFPCM-B3LYP/6-311++G(d, p) level. The eleven structures of the hydrogen-bonded 4AP clusters formed with different number water molecules in both S0 and S1 states were optimized. The absorption, fluorescence and infrared spectra were calculated. The results of the hydrogen bond energy and length reveals that the hydrogen bonds formed by the nitrogen atom of the amine group with water molecule (A type) are significantly weakened from states S0 to S1. In contrast, the hydrogen bonds formed by the oxygen atoms of the two carbonyl groups (B type) with water molecules and those formed by the two hydrogen atoms of the amine group (C type) with water molecules are remarkably strengthened. Comparing with the 4AP monomer spectra, the weakening for the hydrogen bond of A type could be responsible for the blueshifts of the electronic absorption spectra and the stretching vibrational spectra of the two NH groups in 4AP from states S0 to S1. The significant redshifts of the electronic spectra and the S0-S1 downshifts of the stretching vibrational modes of the two NH groups and the two carbonyl groups in 4AP could be attributed to the strengthening of hydrogen bonds for B and C types.

Structural, vibrational and DFT studies on 2-chloro-1H-isoindole-1,3(2H)-dione and 2-methyl-1H-isoindole-1,3(2H)-dione

The Fourier transform infrared (FTIR) and FT-Raman spectra of 2-chloro-1H-isoindole-1,3(2H)-dione and 2-methyl-1H-isoindole-1,3(2H)-dione have been measured in the range of 4000-400 and 4000-100 cm(-1), respectively. Complete vibrational assignment and analysis of the fundamental modes of the compounds were performed using the observed FTIR and FT-Raman data. The geometry was optimised without any symmetry constraints using the DFT/B3LYP method with 6-31G(d,p) and 6-311++G(d,p) basis sets. The vibrational frequencies determined experimentally are compared with those obtained theoretically from DFT gradient calculations employing the B3LYP/6-31G(d,p) and B3LYP/6-311++G(d,p) methods for the optimised geometry of the compounds. The structural parameters and normal modes of vibration obtained from DFT method are in good agreement with the experimental data. The force fields obtained from DFT method were utilised and the potential energy distributions of all the fundamental vibrations of the compounds were calculated.

Ultrashort-lived excited states of aminophthalimides in fluid solution

The Sn-->S0 ultraviolet fluorescence spectra (270-380 nm) of 4-aminophthalimide (4AP) and its N-methyl derivative 4-amino-N-methylphthalimide (4ANMP) are reported, following the absorption of two laser pulses. In polar but non-hydrogen-bonding solvents, both molecules exhibit a principal emission maximum near 290 nm, whereas solutions in hydrogen-bonding solvents display two prominent emission bands, near 300 and 350 nm. The relative intensities of these bands depend on solvent type and, in a pump-probe experiment, on the wavelengths and temporal spacing of two ultrashort pulses. Experiments covering the range approximately 0.1-100 ps showed evidence for at least two distinct ultrashort relaxation processes, the rates of which depend on solvent. Fluorescence upconversion experiments at < 0.2 ps resolution have shown that the longer-duration process correlates with the fluorescence Stokes shift, and provide evidence that the solvent-dependent shift of the S1-->S0 fluorescence spectrum is reflected in the fluorescence quantum efficiency of a nearby electronic state.