Rigidified Push–Pull Dyes: Using Chromophore Size, Donor, and Acceptor Units to Tune the Ground State between Neutral and the Cyanine Limit

Abstract

Scheme1.Neutral N and charge-separated zwitterionic Z resonance structures of merocyanines. [9,10] [a] J.

Fluorophobic Effect Promoting Lamellar Self‐Assembly of Donor Acceptor Dyes

“…Whereas none of the dodecyloxy‐substituted chromophors A‐n‐C12 H studied previously showed any mesomorphic properties, all newly prepared dyes A‐n‐Do F with perfluorinated tails displayed liquid crystalline behaviour. The mesomorphic properties of NC‐n‐Do F , Mal‐n‐Do F and Barb‐n‐Do F (n=1–3) were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X‐ray diffraction (XRD).…”

“…Malononitriles Mal‐n‐OC12 F displayed emission maxima in the range λ max,em =453–598 nm, while the corresponding λ max,em values of barbiturates Barb‐n‐OC12 F were between 478 nm and 640 nm (Table S4). In comparison with aliphatic compounds A‐n‐Do H , the Stokes shifts of 1 H ,1 H ‐perfluorinated dyes A‐n‐Do F were smaller by 15–38 nm. With increasing chromophor size the emission maxima were bathochromically shifted for each series.…”

“…For derivatives Mal‐3‐OC12 F and Barb‐3‐OC12 F , LUMO energies were calculated from the half wave potential according to Bazan . These values are listed in Table and compared with LUMO energies of aliphatic analogues Mal‐3‐OC12 H and Barb‐3‐OC12 H from ref . Upon comparison of the acceptor moieties, barbiturates Barb‐3‐OC12 F and Barb‐3‐OC12 H showed smaller LUMO energies of 0.15 eV and 0.14 eV in relation to their malononitrile counterparts Mal‐3‐OC12 F and Mal‐3‐OC12 H .…”

“…Therefore, Keto‐3‐OH was reacted with a 1 H ,1 H ‐perfluorinated triflate yielding Keto‐3‐Do F in 15 %. After introduction of the donor group, the synthesis of the acceptor moiety followed our previously established route . Ketones Keto‐n‐Do F were submitted to a HWE reaction with diethyl cyanomethylphosphonate to give nitriles NC‐n‐Do F in 62–84 % yield.…”

“…Recently, we investigated the absorption and emission properties of mono‐, bi‐ and tricyclic donor acceptor dyes A‐n‐Do H (n=1, 2, 3) carrying dodecyloxy and piperidyl donor units and keto, malodinitrile and N,N ‐dimethylbarbiturate acceptor units (Scheme ) . Experimental and theoretical results revealed the shift of the ground state polarity from the neutral resonance form N favored by dyes with dodecyloxy donor moiety irrespective of the chromophor size to the zwitterionic resonance form Z favored by dyes with a combination of strong piperidyl donor and barbiturate acceptor . Further studies on related systems were devoted to solvatochromic effects, dichroism and photostability as well as solid state properties .…”