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The electronic absorption spectra of [3,3]-paracyclophadiyne and [4,4]-paracyclophadiyne have been investigated in solution and in the crystalline state. A trans-annular interaction between the diacetylene group and the benzene ring has been found, and a theoretical study has been made to confirm the assignment. The bathochromic shift and the CT band from the benzene ring to the diacetylene group are particularly noticeable for [3,3]-paracyclophadiyne, where the inter-group distance is significantly shorter than the normal van der Waals distance.

The electronic absorption spectra of 2,4-hexadiyne-1,6-diol, diphenylacetylene, and diphenyldiacetylene were measured in a single crystalline state with a polarized light. The results of the polarization measurement and the theoretical calculations gave confirmative assignments of the electronic transitions of these molecules.

The crystal structure of (+)-2,5-dimethoxy-8-chlorotriptycene has been investigated by the X-ray method. The crystal system is monoclinic, and the space group is P21. The cell dimensions are a=8.231, b=13.320, c=8.156 Å, and ß=96.49°. The structure was deduced from the Patterson map and from the calculation of the R-factor minimized by varying the rotational and translational parameters. The structure parameters were refined by the block-diagonal least-squares method by using 1227 independent reflections; the final R-value was 0.073. The absolute configuration was determined to be 1R6S from the CuKa anomalous scattering of the chlorine atom.

The electronic absorption and emission spectra of α and β forms of perylene have been investigated. The lowtemperature spectra have been studied with the (001) plane, and adetailed vibrational analysis is presented. The reflection measurements with the (001) plane and the (110)or (1\bar10) plane are carried out, and the Kramers-Kronig transformation is carried out in order to obtain the absorption coefficient. The results present reasonable evidence for the existence of the intermolccular CT transition in the 27000 cm−1region. The emission spectra at 4.2 K present several novel features of the mechanism of a monomer-like emission of the α-crystal.

Cyclohexane-1,4-dione is an aliphatic ketone with two carbonyl groups. The absorption due to the n–π*transition of the carbonyl group extends from the 30000 cm−1to the 42000 cm−1region. The transition is symmetrically forbidden and is assigned to the A1-A2transition in the C2vsystem. The spectra in the crystal and in a solution of EPA at 77°K show only prominent carbonyl stretching vibrations. The polarized single crystal absorption spectra at 4.2°K are composed of many sharp lines; the vibrational structures are analyzed in detail. The 0–0 transition is observed at 31408 cm−1; the distinct basic frequencies of the excited state are 1096, 790, 557, 375, 247, and 122 cm−1, while the lattice vibrations are 61, 32, and 22 cm−1. The transition is explained by the vibronic coupling mechanism, assuming the C2vsymmetry for the carbonyl group. Two different types of progressions are noticed; one is induced by the out-of-plane b2-type vibration, while the other is allowed by the a2-type vibration. The dichroic properties of the crystal spectra allowed the assignment of the vibrational modes. These vibrations are compared with the infrared and Raman spectral data.

The magnetic susceptibilities and the electron spin resonances of Wurster’s blue bromide, blue iodide, and red bromide have been measured over a wide temperature range. The results show that the paramagnetism of Wurster’s blue bromide above 210°K and of iodide can be explained by the linear Ising model, consistent with the crystal structure. Wurster’s blue bromide showed a deviation from the linear Ising model below 210°K; the dimer model is most appropriate for the explanation of the experimental data.The intensities of the single ESR line are consistent with the results of the static susceptivility measurements. The hyperfine structures are not observed, perhaps because of the rapid movement of the triplet exciton. The magnetic results are explained in terms of the J-values, the origin of which are discussed on the basis of the interaction between the charge-transfer states and the singlet state. The values are resonably correlated with the interaction parameter, β, as estimated from the crystal structure and the electronic spectral measurements.

The electronic spectra and the intermolecular interaction of Würster’s radical have been studied for the dimer state and for the crystalline states. The polarization properties of the excited states have been investigated in detail, and the longest wavelength absorption band of the dimer has been established as having a charge-transfer character. The strength of the charge-transfer band and the shift of the monomer band in the dimer or in the crystalline states are shown to be intimately correlated with the strength of the intermolecular interactions between the stacked radicals. A theoretical analysis of the excited state of the dimer and the crystals is presented; the results are in good agreement with the experimental findings.

The mechanism of the intensity gain of the n–p*transition has been investigated in several carbonyl compounds; (1) cyclohexane-1,4-dione, (2) d-a-bromocamphor, (3) bromonoranisatinone, (4) d-a-cyanocamphor, and (5) spiradine A methiodide. The results on the polarized absorption spectra of single crystals at room temperature have revealed that several mechanisms are involved in the appearance of the carbonyl n–p*band. These mechanisms, (1) the vibronic coupling, (2) the lowering of the symmetry properties of the nand p orbitals by the substituent perturbations, and (3) the charge transfer from the substituents, are discussed theoretically and compared with the experimental results. It is shown that the in-plane components, either parallel or perpendicular to the carbonyl axis, are predominant as the source of the band intensity. The ratio of intensities parallel and perpendicular to the carbonyl axis is estimated by the use of the polarization results.

The electronic structures and electronic spectra of 1-chloro-1-nitrosocyclohexane, nitrosyl chloride, methyl nitrite and dimethylnitrosoamine were studied by making molecular orbital calculations and by measuring the electronic absorption spectra. Concerning 1-chloro-1-nitrosocyclohexane, the n?p*and p?p*bands were observed at 650 and 160 mµ respectively. The conjugation effect of electron donors such as Cl, OCH3and N(CH3)2upon the electronic spectrum of the nitroso group was studied. The intramolecular charge-transfer bands characteristic of the donor-acceptor interaction were found at 190, 210 and 230 mµ for nitrosyl chloride, methyl nitrite and N,N-dimethylnitrosoamine respectively. This shows that the intramolecular charge-transfer bands appear at longer wavelengths in the order of the increasing ability of the electron donors, Cl

The electronic absorption spectra of three crystalline modifications of anthracene derivatives have been measured; they are the a and ß form of 9, 10-dichloroanthracene and 9, 10-dibromo-anthracene. The assignment has been presented for each absorption band. The charge transfer absorption which is regarded to the transition between two stacked molecules has been observed in the a-form of 9, 10-dichloroanthracene; also a Rydberg type transition which has an out of plane polarization is found in this crystal starting at 290 mµ. It is unusually broad and is regarded as a band to band transition. The emission band has been measured at different temperature; it is found that excimer type emission is most prominent in the ß-form of 9, 10-dichloroanthracene, in which intermolecular approach in the excited state will occur with less difficulty. A criterion for strong, medium, and weak interactions in the excited state is presented by comparing the shift, and the shape of the emission band with the intermolecular vibrational spacing. These results show that the charge transfer interaction and excimer formation are greatly dependent on the relative orientation of molecules, the p-electron overlap, and the difficulty of intermolecular approach in the excited state, particularly with its correlation to the steric repulsion of the bulky substituent groups.

The structure of the Meisenheimer complex has been determined by the X-ray method. The complex is characterized by a symmetrical structure, in which the two methoxyl groups are nearly equivalent to each other. The results showed a peculiar shape of the reaction intermediate, the substituted carbon atom is transformed into a tetrahedral shape, while the planarity of the whole molecule is kept with an increased conjugation between the nitro group and the ring system.

Ultraviolet absorption spectra of thioacetamide and thiourea are measured under various conditions. In aqueous solution, three bands (210, 261 and 318 mμ) for thioacetamide and two bands (195 and 236 mμ) for thiourea are observed. Further, polarized ultraviolet absorption spectra are measured with their crystals. On the basis of the results regarding the polarized ultraviolet absorption spectra, the directions of transition moments can be determined as follows : 1) the directions of transition moments of the 261 and 210 mμ bands of thioacetamide are approximately parallel to the axis connecting the nitrogen and sulfur atoms and connecting the nitrogen and methyl carbon atoms, respectively, 2) the directions of transition moments of the 236 and 195 mμ bands of thiourea are parallel and perpendicular to the C=S axis, respectively. From the combination of the experimental results concerning the directions of transition moments with theoretical consideration based on semi-empirical LCAO treatment including configuration interaction, the assignment of the four absorption bands under consideration are finally determined. One of the noticeable conclusions is that the 195 mμ band of thiourea can be regarded as a typical intramolecular charge-transfer absorption.It is shown that in the hydrochloric acid solution of thioacetamide the 261 mμ band decreases its intensity and a new band appears at 237 mμ. By measuring the dependence of intensities of these two bands upon the acid strength of the solution, it is concluded that the 237 mμ band is due to the conjugate acid of thioacetamide. The pKBvalue of thioacetamide is determined spectrophotometrically to be 1.2 at 24.5°C. From the comparison of the wavelength of the peak absorption of thioacetamide with that of its conjugate acid, it is seen that the proton is conceivably attached to the amino group.

A new crystalline form of perylene has been found and its crystal structure has been determined by the two-dimensional X-ray diffraction method. The new form is monomeric, while the previously known form has a dimeric structure. The electronic absorption and fluorescence spectra of both forms have been measured ; on the basis of these data, an assignment is proposed for the observed transitions. Although the fluorescence spectrum of the monomer form shows a small shift, that of the dimer form shows a larger shift than would be expected from the absorption spectrum. This is explained as a stabilization of the lowest excited singlet state by a charge-transfer resonance interaction between the molecules in a pair. Because this stabilization increases as the distance between two molecules decreases, it is suggested that the molecules in a pair approach each other after excitation. At the liquid helium temperature the motion of molecules in the crystal will be frozen out, the larger stabilization of the excited level cannot occur, and the green emission which is characteristic of the monomer form is observed from the dimer form. The rate process of the molecular motion at lower temperatures has been analyzed.

The electronic absorption spectra of some substituted benzene molecules p-nitroaniline, benzoic acid, acetanilide, trans-cinnamic acid, and durene have been measured in ethanol or n-heptane solutions and as single crystals, using polarized light. The measurement of the crystalline spectra reveals in many respects the properties of the transitions of substituted benzene molecules. The 277 mμ of durene, which is reasonably regarded as a band analogous to the 260 mμ of benzene, is shown to be polarized perpendicular to the two-fold symmetrical axis of the molecule. Bands of the same type occur at 264 mμ in p-nitroaniline (crystal), at 284 mμ in benzoic acid, at 282 mμ in acetanilide and at 299 mμ in trans-cinnamic acid. In addition, those molecules in which the benzene ring is substituted by the electron-accepting groups, show a strong band, associated with intramolecular charge transfer, in the near ultraviolet region. The 370 mμ band of p-nitroaniline is shown to be polarized parallel to the long axis of the molecule, and the 230 mμ band of benzoic acid has a polarization parallel to the line connecting the centers of the benzene ring and the carbonyl group. The directions of the transition moments of the 240 mμ band of acetanilide and the 276 mμ band of trans-cinnamic acid are also shown to be on the line connecting the substituents and the benzene ring. Davydov splitting is observed in the crystal of p-nitroaniline; this splitting is in good agreement with the values calculated by the exciton theory.

The mechanism of the aromatic substitution was studied on the basis of the energy level diagrams determined for both the aromatic molecule and the reagent. From the consideration of the relative heights of the highest occupied and lowest vacant orbitals of the former to those of the latter, it was deduced that a large electron transfer occurs at some stage of the reaction from the aromatic molecule towards the reagent for the electrophilic substitution and in the reverse direction for the nucleophilic substitution.In connection with this electron transfer mechanism, it was expected that the orientation rule observed with the aromatic substitution can be explained by free valency values of the aromatic cation, neutral molecule and anion for the electrophilic, radical and nucleophilic substitutions respectively. It was shown that this expectation is fully satisfied for various aromatic substitutions.

The electronic structures and spectra of thymine, uracil, and their derivatives have been studied by measuring the electronic absorption spectra of the single crystals. In the polarized absorption spectra of the crystal, an unusual absorption band appears at about 285 mμ in the tail of the usual π→π*transition when the crystal has the C=O···H–N-type hydrogen bond. The direction of the transition moment of this band is found to be along the direction of the hydrogen bond between a pair of C=O···H–N-groups, the nature of which is discussed from several viewpoints. The direction of the transition moment of the first and second π→π*bands is determined to be inclined at about +38° and +86° from the C4···N1line toward the C5atom. The result for the first band is not in perfect agreement with the finding of Stewart and Davidson regarding 1-methylthymine, who regarded this angle as either −14° or +19°.

Mulliken’s charge-transfer type molecular complexes between iodine and various aliphatic amines were studied spectrophotometrically in n-heptane solutions. The electron donor components used in the present study include ammonia, primary amines (methyl-, ethyl- and n-butyl-), secondary amines (dimethyl-, diethyl-and piperidine), and also tertiary amines (tri-methyl-, tri-n-propyl- and tri-n-butyl-). The charge-transfer absorption bands characteristic of molecular complexes of this kind appeared between 229 and 281 mμ depending on the kind of amines used as electron donors. The stable equilibria of 1:1 complex formation were verified for all the systems. The equilibrium constants (K) were determined at various temperatures and the heats of formation (ΔH) and entropy changes (ΔS) were evaluated. The values of ΔHrange from −4.8 kcal./mol. for ammonia complex to −12.3 kcal./mol. for tri-n-butylamine complex, and ΔSalso changes from −8.0 e. u. for the former and −27.8 e. u. for the latter. The effect of successive replacement of hydrogen atoms of ammonia by methyl or ethyl groups on the value of ΔHwas shown to be additive. From the data of ΔHand ΔSit was concluded that there exists a linear relation between these two quantities for the iodine complexes with all the primary amines and secondary amines having rather small substituent groups like methyl. The deviation from the linear relation was observed with the complexes including diethylamine and tertiary amines as electron donors. These amines with bulky substituent groups may be expected to exert a great steric hindrance in the case of the molecular complex formation. Further it was shown that the plots of ΔH’s against σ*’s (Hammett’s substituent constant) fit the straight line, except for those of the iodine complexes with triethylamine, tri-n-propylamine and tri-n-butylamine. With the aid of the spatial configuration derived from X-ray crystal analysis data for the trimethylamine-iodine complex, one could evaluate the three parameters (over-lap integral (s), exchange integral (β) and effective electron affinity (A)) which are necessary for explaining reasonably the relation between the transition energies of the charge-transfer bands and the ionization potentials of electron donors. For example, the β values thus estimated were −2.09, −2.20 and −2.32 eV. for the complexes with primary, secondary and tertiary amines, respectively.

The electronic absorption and fluorescence spectra of the single crystal of the anthracene-s-trinitrobenzene complex have been measured, and the polarization property of electronic transitions has been discussed in terms of interaction between the no-bond structure, the charge transfer and the locally-excited state of anthracene.It has been shown that molecules in a pair are displaced to a closer position after the excitation, whereby the mixing of the donor-excited level occurs more than in the ground state (Frank-Condon state), and the fluorescence involves a larger contribution from the in-plane transition of anthracene.

The electronic absorption spectra of single crystals of pyrene, chrysene, azulene, coronene and tetracene have been measured by a polarized light. Some crystal absorption bands exhibit appreciable splittings and changes in intensity relations according to the simple exciton theory. Those results are explained by the use of the second-order exciton calculation without the inclusion of the electron overlap effect. The theoretical results give a fairly reasonable explanation of crystal spectra, and it has been shown that the second-order mixing of excited states plays an essential role in modifying the crystal spectra from the pattern of the free molecule.

The polarized absorption spectra of crystals of indole derivatives have been measured in order to confirm the presence of two types of electronic transitions, 1Lband 1La, in the long-wavelength absorption region, and in order to determine the direction of their transition moments. The polarization spectra show that the 1A–1Lbelectronic transition forms a sharp absroption band with vibrational structures lying below a broader absorption band of the 1A—1Latransition. The transition memont direction of the 1Lbmakes an angle of 54° to the long axis of the molecule, while that of the 1Lalies at an angle of −38° to the same axis. These results were compared with the results of theoretical calculations of the P–P–P SCF MO–CI method.

Crystals of (-)-2,2'-bisbromomethyl-l'-binaphthyl have been subjected to crystal structure analysis in order to determine the absolute configuration of optically active 1,1'-binaphthyl derivatives. The crystals are orthorhombic, space group P212121with Z=4 and the lattice constants are; a=10.360, b=13.052, c=13.178 Å. The structure was solved by the heavy atom method and the final Rindex was 0.064. The absolute configuration was determined as (S)-configuration by utilizing the anomalous dispersion effect of bromine atom.