Simple zwitterionic merocyanines as potential NLO chromophores

Abstract

A suite of zwitterionic pyridylidene-based merocyanines that contain no interconnecting p-bridge between the donor and acceptor rings has been synthesised and their second-order NLO properties evaluated largely by semi-empirical computational methods (MOPAC 97/AM1). Contrary to expectation, increasing the degree of inter-ring twist (h), at least up to 55u, in these new pyridylideneazolone chromophores is found to have little or no effect on the figure of merit [mb( 0 )]. An X-ray crystallographic appraisal of one of these chromophores, 14, reveals however that the twist angle (albeit in the solid state) is greater than that predicted by computation and that all other features are consistent with the highly zwitterionic nature of these systems. In spite of this, a combination of factors-insufficient acceptor strength, insufficient extent of conjugation and perhaps insufficient twist angle, in particular-clearly leads to the low values of the quadratic hyperpolarisabilities. The trade-off between targeting a more modest b from a minimum of p-conjugating framework between D and A (and therefore synthetic expediency) and seeking a moderate-to-high dipole moment has therefore resulted in only low figures of merit for these systems.Calculations performed on a suite of readily accessible, isoelectronic cyanines, in which the acceptor is a stabilised cyclopentadienide carbocycle rather than a heterocycle, have revealed the potential that these systems, exemplified by 27, have as NLO chromophores. Representative polymer-tetherable derivatives of this system have been prepared as have the corresponding TDI-based polyurethanes.

Synthesis, linear & non linear optical (NLO) properties of some indoline based chromophores

“…Furthermore as the coupling constants observed for the vinylic protons of the conjugated interconnects are of the order of 12e15 Hz this confirms that they are in an all-trans configuration [23]. This is in contrast to our previous observations for zwitterionic compounds such as 1 and 2, where detailed NMR studies showed two isomers to be present and that these were due to rotational isomerisation about the acceptor ring and conjugated interconnect [14]. The absence of such rotamers in the present compounds is likely due to them being far less charge separated in their ground states (confirmed from X-ray crystallographic studies discussed later in the work), than, for example, 1 and 2.…”

“…The methodology used to prepare 7e9 and 11 relies on an approach previously described by us [14] and which utilizes the N-phenylacetamide precursors 4e6 and 10. Reaction of these precursors with 1,1,3-trimethyl-2-methyleneindoline, 3, in alcohol afforded chromophores 7e9 and 11 as colored solids in yields of 36e87%.…”

Orientation and Solvatochromism of Dyes in Liquid Crystals

“…Merocyanine compounds 1, 2 and 3 were synthesised according to [13] and MORPIP were synthesised according to [14]. The structures of the compounds are shown in figure 1.…”

Total Synthesis of Isodesmosine by Stepwise, Regioselective Negishi and Sonogashira Cross‐Coupling Reactions

“…The 3,5-regioselective iodination of 11 with I 2 under reflux conditions gave 2-hydroxy-3,5-diiodopyridine (12) in 95 % yield. [17] The hydroxy group of 12 was then converted into the bromide using phosphorus tribromide (PBr 3 ) at 145°C to afford 2-bromo-3,5-diiodopyridine (6) in 95 % yield. Interestingly, the bromination did not proceed with N-bromosuccinimide (NBS).…”