Kimihiro Hiruta

Effect of Solvent Polarity and Acidity on Fluorescence Emission Fine Structures of Select Aza-Polynuclear Aromatics and Dibenzo[b,n]Perylene Hetero-Atom Derivatives

Fluorescence emission spectra are reported for 1-azabenz[a]anthracene, 2-azabenz[a]anthracene, 9-azabenz[a]anthracene, 4-azachrysene, 1,2,7,8-tetraazacoronene, dibenzo[2,3:10,11]perylo[1,12bcd]furan, dibenzo[2,3:10,11]perylo[1,12bcd]thiophene, and dibenzo[2,3:10,11]perylo[1,12bcd] selenophene dissolved in various organic solvents. Results of these measurements are used to classify the solutes into probe or nonprobe molecules depending upon whether emission intensity ratios vary systematically with solvent polarity. Of the eight aromatic solutes examined, only the three azabenzanthracenes showed slight probe character.

Precise PPP molecular orbital calculations of the excitation energies of polycyclic aromatic hydrocarbons. Part 2: Evaluation of the spectrochemical softness parameter based on the spectroactive partial structure of a molecule

For precise Pariser-Parr-Pople molecular orbital (PPP MO) calculations, the values of the spectrochemical softness parameter (k) of a new two centre electron repulsion integral (new-γ) were evaluated based on an appropriate partial structure of cata-condensed polycyclic aromatic hydrocarbons (PAHs). The spectroactive aromatic sextet resonance system [ASRS] was defined as a spectroactive partial structure of a molecule. The calculated excitation energies of the p-band of the cata-condensed PAHs accurately reproduced the observed values. In particular, the calculated energies of branched PAHs were improved compared with those obtained using our previous method.

Precise PPP molecular orbital calculations of excitation energies of polycyclic aromatic hydrocarbons part 3. Evaluation of the spectrochemical softness based on the model of composite molecules

Abstract For Pariser-Parr-Pople molecular orbital (PPP MO) calculations of the p -band of polycyclic aromatic hydrocarbons (PAHs), the values of spectrochemical softness parameter k of a novel two-centre electron repulsion integral, new-γ, were evaluated based on the model of composite molecules (MCM). The spectroactive portion (SP), namely the part which contributes mainly to the p -band, of a molecular framework was used as an index for the evaluation of the parameter k for peri -condensed PAHs together with cata -condensed PAHs. The calculated excitation energies of the p -band of PAHs using the new-γ included k values based on the SP reproduced accurately the observed ones. The precise MO calculations were performed.

Precise PPP molecular orbital calculations of excitation energies of polycyclic aromatic hydrocarbons. Part 5: Spectroactive portion of fluoranthene derivatives☆

Abstract For Pariser–Parr–Pople molecular orbital (PPP MO) calculations of the p -band of fluoranthene derivatives, the values of the spectrochemical softness (SCS) parameter k in a novel two centre electron repulsion integral new-γ were evaluated based on the spectroactive portion (SP) of a molecular framework. The SP was determined by the character of MO calculated by the HMO method with reference to the structural analysis by ab initio MO calculations with 6-31G* level. The calculated excitation energies of the p -band of fluoranthene derivatives using the new-γ including k values based on the SP reproduced accurately the observed ones.

Precise PPP molecular orbital calculations of excitation energies of polycyclic aromatic hydrocarbons. Part 4[1] evaluation of the spectrochemical softness using the dewar-type resonance energy

Abstract For Pariser-Parr-Pople molecular orbital (PPP MO) calculations of the excitation energies of the p -band of polycyclic aromatic hydrocarbons (PAHs), the spectrochemical softness parameter k of a novel two centre electron repulsion integral new-γ were evaluated using Dewar-type resonance energies ( REs ). In many cases, the calculated results, using the new-γ, were improved compared with those using the conventional Nishimoto-Mataga γ (N·M-γ) function. The Dewar-type REs could be used as indices of the spectrochemical softness.

Practical PPP molecular orbital calculations of absorption maxima of quinones

Abstract In order to calculate the excitation energies of linear para acenoquinones (LPAs) more accurately by Pariser-Parr-Pople molecular orbital (PPP MO) method, the spectrochemical softness parameter k of a novel two centre electron repulsion integral new-γ are evaluated based on spectroactive portion (SP) in a molecular framework. SP is defined as the longest acene portion, including a quinonoid ring of LPAs. The calculated results using the new-γ are greatly improved compared with those using the conventional Nishimoto·Mataga γ function.

Precise PPP molecular orbital calculations of excitation energies of polycyclic aromatic hydrocarbons. Part 6. Spectrochemical atomic softness parameter

The excitation energies of the α-, β-, and p-bands of benzo-annelated polyacenes were estimated by the Pariser–Parr–Pople (PPP) molecular orbital calculation method using a novel concept for evaluating the two-centre electron repulsion integral, new-γA, in which the spectrochemical atomic softness (SCAS) parameter krA was taken into account. The value of krA was determined using the concept of the spectroactive portion (SP) and allotted to each carbon atom. The calculated results using new-γA were excellent for the simultaneous calculations of the p-, α- and β-bands of benzo-annelated polyacenes and were better than those obtained from the conventional N·M-γ or the usual new-γ. The C–C bond lengths calculated using new-γA reproduced quantitatively the observed values.

Practical PPP molecular orbital calculations of absorption maxima of quinones.Part 2. Evaluation of the spectrochemical softness based on the absolute hardness

Abstract The first absorption maxima of linear para acenoquinones (LPAs) were calculated by the Pariser–Parr–Pople molecular orbital (PPP MO) method using a novel, two-centre electron repulsion integral new-γ. The spectrochemical softness parameter k in the new-γ was evaluated from the absolute hardness, η PPP and η HMO , which were obtained by the PPP MO and the HMO level approximations, respectively. The first absorption maxima calculated using the new-γ with k obtained from η PPP are greatly improved to reproduce the observed values better than using the conventional Nishimoto·Mataga-γ function.

PPP Molecular Orbital Calculations of Polyenyl Cations and their Analogs using New-γ and Pseudo Atom Modeling

Abstract The first absorption bands of the tetramethyl polyenyl cations were calculated by the Pariser-Parr-Pople molecular orbital method. By considering the extraordinary hyperconjugation effect of methyl substituents and using the new-y, the calculated absorption wavelengths reproduce well the observed ones.

MS-Windows Application for a PPP Calculation using the Novel Two-Center Electron Repulsion Integral

Abstract The application of Windows 95/98/NT for PPP MO (Pariser-Parr-Pople molecular orbital) calculation was developed by using the Inprise C++ builder. The novel two-center electron repulsion integral (new-γ), the concept of spectrochemical softness parameter krs for PPP calculation, was introduced in this application. The user can perform quickly the modeling of π-conjugated compounds on a PC monitor and select many suitable parameters (for example, ionization potentials, resonance integrals etc.) for the PPP calculation. The SCF calculation was momentarily performed and oscillator strength and LCAO coefficients of HOMO, LUMO or others were displayed. The calculations gave satisfactory results for the prediction of the electronic absorption spectra of polycyclic aromatic hydrocarbons(PAHs), symmetric cyanins and so on.