Große elektrische Feldeffekte auf die dipolare Aggregation von Merocyaninfarbstoffen

Fluorescent H‐Aggregates of Merocyanine Dyes

“…This weak band may emanate from vibronic coupling or a small rotational twist between the two chromophores. Indeed, the latter interpretation is in accordance with our earlier electrooptical absorption (EOA) studies that revealed a small ground‐state dipole moment for these dimer aggregates 12. 17 On the other hand, X‐ray crystallographic data11 as well as the optimized dimer geometry according to MP2/6‐31G(d,p) calculations18 show a perfectly centrosymmetric dimeric unit as the energetically preferred geometry (Figure 4)…”

“…As a consequence, these dimer aggregates exhibit a high thermodynamic stability in solvents of low polarity and a well‐defined centrosymmetric geometry (Scheme 1) 11. 12 These two aspects are advantageous attributes for the current study; ionic cyanine dyes, in contrast, exhibit less predictable aggregate structures and aggregation free enthalpies. Although several of our merocyanine dyes, for example, dyes 1 – 3 were found to form fluorescent dimers,13 we will focus our attention on merocyanine dye 2 , whose high solubility enabled concentration‐dependent investigations even in low‐polarity solvents 14.…”

Hydrogen‐Bond‐Directed Head‐to‐Tail Orientation of Dipolar Merocyanine Dyes: A Strategy for the Design of Electrooptical Materials

“…[4] However, the efficiency of this field-induced poling approach is hampered by the thermodynamically favored antiparallel aggregation of dipolar dyes to give dimers with extinguished dipole moments (Figure 1 a). [5,6] This kind of H-aggregated dimer has been established as the predominant supramolecular species arising from pushpull chromophores [6] in NLO and PR materials at the required high concentrations (> 20 wt %), while the desirable parallel orientation (Figure 1 b) has not been realized to date in a thermodynamically equilibrated system. [7,8] Here we introduce a supramolecular approach in which a receptor is employed to orient two merocyanine dyes in the desirable head-to-tail parallel fashion through multiple hydrogen bonding.…”

Hydrogen‐Bond‐Directed Head‐to‐Tail Orientation of Dipolar Merocyanine Dyes: A Strategy for the Design of Electrooptical Materials

“…[1][2][3] Nevertheless, exploitation of optimized molecular properties at the macroscopic level remains a challenge. [5,6] This kind of H-aggregated dimer has been established as the predominant supramolecular species arising from pushpull chromophores [6] in NLO and PR materials at the required high concentrations (> 20 wt %), while the desirable parallel orientation (Figure 1 b) has not been realized to date in a thermodynamically equilibrated system. [4] However, the efficiency of this field-induced poling approach is hampered by the thermodynamically favored antiparallel aggregation of dipolar dyes to give dimers with extinguished dipole moments (Figure 1 a).…”

“…For technologically promising polymer composite materials, optimized molecular properties m, a, b, and g must be transformed into optimized macroscopic susceptibilities by appropriate orientation of the dipolar dyes by an external electric field. [5,6] This kind of H-aggregated dimer has been established as the predominant supramolecular species arising from pushpull chromophores [6] in NLO and PR materials at the required high concentrations (> 20 wt %), while the desirable parallel orientation (Figure 1 b) has not been realized to date in a thermodynamically equilibrated system. [5,6] This kind of H-aggregated dimer has been established as the predominant supramolecular species arising from pushpull chromophores [6] in NLO and PR materials at the required high concentrations (> 20 wt %), while the desirable parallel orientation (Figure 1 b) has not been realized to date in a thermodynamically equilibrated system.…”