Aggregated Structures in Langmuir−Blodgett Films of Pyridinium−Dicyanomethanide Dyes

Langmuir−Blodgett Films of a New Pyridinium−Dicyanomethanide Dye and Their Potential Optical Applications

“…In any case, micrographs of these LB films give clear proof of the presence of aggregates. 13 The spectral change could be attributed to the interaction of the electronic transition moments of the chromophore in the multilayer. According to the simplified molecular exciton model, an electronic transition band shifts to the shorter wavelength, when chromophores are arranged with their transition moments parallel and ordered perpendicular to the stacking direction (H-aggregate structure).…”

“…LB films were transferred from a pure water subphase at π ) 15 mN/m (T ) 291 K) onto quartz slides using the KSV 3000 balance for Y-type LB films (i.e., films with a head-to-head and tail-to-tail packing of the amphiphilic molecules). Y-and Z-type LB films (Z-type are LB films with a head-to-tail packing of the molecules where the polar heads of the first molecular layer are in contact with the solid substrate) were obtained using a KSV 5000 balance under the same conditions of subphase temperature and surface pressure (the KSV 5000 balance is a two-compartment LB trough Langmuir 1997, 13 with asymmetrical compression of the monolayer; i.e., only one barrier moves and compresses the monolayer). The dipping rates for the upstroke and the downstroke ranged from 8 to 20 mm/ min, obtaining differently structured LB films depending on the specific conditions that were chosen (see Results and Discussion and Table 1).…”

Poled sol–gel materials doped with heterocycle-based push–pull chromophores with second-order optical non-linearity

“…1), but also a shoulder around 580 nm, attributed to a dimeric form of BisOH.PETCN, is often detected [21,22,16], that is now visible in the case of doping only with the chromophore; in this case also the presence of an intense narrow band at 440 nm is evident, that can be attribute to high order aggregates, of the type of Ôdeck-of-cardsÕ [23]; their presence is revealed also as a macroscopic defect of the films that are clearly not homogeneous. By co-doping with the CbOH molecule (CbOH, Scheme 1) the intense narrow band at 440 nm is absent and the presence of the shoulder around 580 nm of the dimeric units is less evident, confirming that the introduction of CbOH units strongly reduce 1660 1640 1620 the chromophore aggregation that would occur at this concentration, allowing to achieve higher chromophore loadings with a good dispersion within the matrix.…”

Hybrid glass-like films through sol–gel techniques

“…A broad intense absorption band is clearly visible, peaked around 630 nm, due to BisOHPETCN intramolecular charge transfer (ICT) from the negatively charged dicyanomethanide group to the positively charged pyridinium ring that determines the transition from the zwitterionic ground state to the neutral excited state. An intense narrow band at 440 nm is, however, also present, that was attributed to aggregation of the chromophore in a structure of the type 'deck-of-cards' [8]; this aggregation give rise to inhomogeneity of the film, visible at the naked eye ( Fig. 3(a)).…”