Self-aggregates formation of 3,4,9,10-tetra-(n-alkoxy-carbonyl)-perylenes in Langmuir–Blodgett films

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

“…6(b) and 7(b)]. As the concentration of the dye rises, small broadening of the fluorescence band at the red side appeared, especially for the dyes with short alkyl chains (1-3), similar as it was observed for the monolayer of pure 3,4,9,10-tetra-(n-alkoxy--carbonyl)-perylenes on quartz slides [8][9][10]14,15]. Thus, taking into account the shape of the fluorescence spectrum we can suggest that Y-type emission with only small contribution of E-type emission occur for LB films made of one layer of dyes 1-6 and their mixtures with arachid acid.…”

“…This leads to the conclusion that increasing number of layers and/or dye concentration in the LB film is favourable for such interaction between two molecules of perylene derivatives which gives genuine excimer emission. The same observation was made for dye 2 after 3-fold deposition of the Langmuir film onto quartz slides at the surface pressure behind the collapse point (corresponding to the condensed phase of the floating monolayer) [9,15], meaning that the high molecular organization is conducive to excimer creation too. Moreover, it should be noticed that with the rise of the layers number and the dye concentration the maximum of the long-wavelength fluorescence peak shifts towards longer wavelengths and for LB films of 6 layers and MF of the dye equal to 0.5 appears at 600 nm for 1, 586 nm for 2, 580 nm for 3, and 575 nm for 4.…”

“…Absorption spectra of LB films formed of 3 layers of dye/AA mixtures, similarly as LB films of the dyes themselves [9,10,14,15], show an extensive broadening and red shift of the maxima of the long-wavelength band. Moreover, the ratio of both maxima in the band is different than in the ethanol.…”

“…In these spectra we observe the structureless broad fluorescence band with the maximum around 550-600 nm and, in some cases, small shoulder at shorter wavelength (»520 nm). A shape of the band depends on the length of the alkyl In our previous papers [8][9][10]14,15] we reported about the fluorescence spectra of LB films formed of dyes 2-6, pure and mixed with two liquid crystals, and supposed that the main emitters in LB films are excimers, which originate from interaction of neighbouring molecules after one is excited. 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).…”

Spectral properties of naphthalimide dyes mixed with 4-heptyl-4′-cyanobiphenyl (7CB) in Langmuir-Blodgett films

“…In these case, the exciton is delocalized over several molecules due to the large intermolecular interactions. Therefore the excimer creation was observed also in the LB films, where the high dye concentration and molecular or− dering favour the aggregation process [12,18,[27][28][29][30][31]. The excimer states decay with a much smaller radiative effi− ciency as compared to monomer states and this effect is re− ferred as to "dye self−quenching" [25,26].…”