Modeling of the Optical Properties of Cofacial Chromophore Pairs:  Stilbenophane

Abstract

Using electronic absorption and fluorescence spectroscopic techniques, as well as quantum chemical calculations, we have studied the electronic spectra of thia-bridged stilbenophane (TSP) with close cofacial contact of two trans-stilbene (t-SB) units. Compared to the t-SB monomer, the experimental consequences of the cofacial arrangement are (i) a splitting of the main absorption band with a weakly allowed emitting state, and (ii) a strongly red-shifted, unstructured emission spectrum with long fluorescence decay times. According to the theoretical investigations, the two t-SB units are strongly bent in the electronic ground state (S 0 ), because of repulsive π-π overlap. In the first excited state (S 1 ), the t-SB units become almost planar, because of attractive π*-π* overlap. As a consequence, the symmetry-forbidden S 0 T S 1 transition couples strongly to interchromophore breathing modes of low frequency (ν 1 ) 67 cm -1 , ν 2 ) 117 cm -1 ), yielding structureless spectra with large Stokes shifts. The features of the calculated spectra are in good agreement with the experimental data. The results indicate that strong intermolecular vibronic coupling is also responsible for "excimer-like" emission in organic molecular crystals of cofacially arranged molecules. Furthermore, the different geometries in the S 0 and S 1 states of TSP give evidence for the mechanism of [2+2]photodimerization of t-SB in solutions.

Violet‐to‐Blue Tunable Emission of Aryl‐Substituted Dispirofluorene–Indenofluorene Isomers by Conformationally‐Controllable Intramolecular Excimer Formation

“…Therefore, the introduction of the aryl arms in 2 c – g has a remarkable effect not only on the emission color (Figure 6, bottom) but also on the quantum yields, which is consistent with the presence of H‐type interaction of the two “aryl‐fluorene‐aryl” in addition to the intramolecular excimers in the case of 2 c – g 7. 11, 53, 54…”

“…For example, in fluorescent molecules, π–π interactions may cause a red‐shift of the emission wavelength by excimer formation 6. Indeed, excimer formation resulting from intramolecular interactions have been widely described in the literature for various systems such as naphthalene,6 oligophenyl based cruciforms,7 ethynyltriphenylene derivatives,8 dibenzofulvene polymers with fluorene side chains,9 carbazolophanes10 and stilbenophanes,11 and various pyrene6, 12–14 and thiophene derivatives 15–18. Despite their importance in the field of organic light emitting diodes (OLED),3–5, 19–23 intramolecular excimer fluorescence of “aryl‐fluorene‐aryl” derivatives have only been very recently investigated 24.…”

Scintillating Metal‐Organic Frameworks: A New Class of Radiation Detection Materials

“…Similarly, thia-bridged stilbenophane exhibits an unstructured and strongly red-shifted emission spectrum. [36] Based on the magnitude of D, the amount of distortion induced by the beam increases in the order SDCH 2 < MOF-S2 < MOF-S1.…”

“…This conclusion is consistent with ab initio calculations predicting that an excited-state distortion in thia-bridged stilbenophane enables low-frequency interchromophore breathing modes to couple effectively with the electronic transition, leading to loss of vibronic structure in the emission spectrum. [36] [a] IBIL data, this study. [b] Ref.…”

Polyvinyl‐Locked versus Free Quaterthiophene: Effect of Spatial Constraints on the Electronic Properties ofn‐Hexylquaterthiophene

“…Indeed, such changes in the emission band shape and the redshift against absorption, with respect to free moieties, are a typical feature of "excimer-like" emission from cofacially arranged molecules. [2,17,27,28] It has also been observed for cofacially oriented anisole-bridged terthiophene moieties [11] as well as for cyclophane-type methylene-bridged dimeric quinquethiophenes in solution. [18] Intermolecular interactions between the triads in the solid state could also contribute to the observed emission band red-shift with respect to free quaterthiophene moieties.…”