The Electronic Spectra of Aromatic Molecular Crystals. II. The Crystal Structure and Spectra of Perylene

Abstract

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 synthesis of novel perylene-like dyes and their aggregation properties in Langmuir and Langmuir–Blodgett films

“…For dye 2 a broad (d ¼ 2400 cm À1 ) structureless fluorescence band with the peak at l ¼ 610 nm is observed. As this band has no mirror band in the absorption spectrum, and its shape and position are similar to perylene excimer fluorescence band, observed by Ferguson [22] as well as for a-perylene crystal [21], it can be doubtlessly attributed to the excimer created in the LB film by two dye 2 molecules from which one is in the excited state. Likewise, as it was mentioned in introduction, the excimer emission for 3,4,9,10-tetra-(n-alkoxy-carbonyl)-perylenes in LB films was found [14e19].…”

Intermolecular interactions in Langmuir-Blodget films of liquid crystalline perylene derivatives

“…The length of the alkyl chains has no influence on the spectral properties of the dyes. The spectra are characteristic of monomer absorption and fluorescence [4,12,13].…”

“…Benning et al [2] have found that the maximum of the excimer fluorescence band of 3,4,9,10-tetra-(n-alkoxy--carbonyl)-perylenes in the crystalline state appears at 582-600 nm (depending on the alkyl chain length). However, in LB films of perylene and its derivatives two types of emission were observed, Y-emission, which originates from partially relaxed excited molecular pairs (excimer precursors) [12,13,22] and E-emission, connected with the existence of genuine excimers [12,13]. The contributions of both emissions to the fluorescence spectra depend on the molecular structure of substituents attached to the perylene skeleton, on the excitation wavelength and on the temperature [16,[23][24][25][26].…”

Physical Vapor Deposited Films of a Perylene Derivative: Supramolecular Arrangement and Thermal Stability

“…[32][33][34][35] The emission of the PhPTCD PVD films was investigated using the 514.5 nm excitation laser line, which spectrum for a 150 nm thickness film on quartz with a maximum at 689 nm shown in Figure 3. The broad and structureless emission band (from 620 nm to 900 nm in this case) found for perylene derivatives is assigned to excimer fluorescence, 36 which is related to molecular stacking that requires the chromophores to be organized parallel and overlapping ring systems. When the excimer relaxes to its ground state, it emits at a …”