Theoretical Studies of a Highly Reactive Diacetylene Monomer, 3,5-Octadiyn-2,7-dione, and Its Cross-Conjugated PDA Oligomers

Abstract

Polydiacetylene derivatives have great potential in the area of nonlinear optics. Several factors affect the usefulness of these materials, and it is desirable to model the effects of these factors before time and resources are spent in the development of new materials. Our work focuses on a particular derivative, 3,5-octadiyn-2,7-dione, ODDO, which related work has shown to be highly polymerizable in solution. The interesting polymer poly-ODDO has acetyl groups cross-conjugated with the conjugated backbone. Calculations show that the monomer's reactivity may be partially explained on thermodynamic grounds. The utility of the AM1 method in MOPAC 6.0 as a model for PDA experimental optical properties is shown. Conformers of ODDO and its oligomers are calculated at high precision using AM1 to see the variation in optical properties and stability as a function of backbone planarity and substituent alignment relative to the backbone, in an effort to determine whether or not there would be any benefit in optical properties to attempts to control the conformation. Analysis of the data indicates that backbone planarity should be important to optical properties, as one would expect, and that substituent orientation has much less effect than one might expect from a cross-conjugated substituent. Specific coplanar orientations are predicted to have a large relative effect on stability but only a minor effect on optical properties. Coplanar ODDO oligomers are predicted to have lower HOMO-LUMO gaps and better third-order nonlinear optical properties than equivalent unsubstituted oligomers. The data also show that monomeric HOMO-LUMO gaps may not reliably predict the relative utility of polymeric nonlinear optical materials.

Molecular Rods. 1. Simple Axial Rods

“…[78][79][80] The occurrence of the polymerization and its course are determined by the mutual orientation of the butadiyne groups. 76 End groups bulkier than hydrogen, such as tert-butyl, triethylsilyl, and phenyl, have an important stabilizing effect. Thus, the tetrayne 29 melts at 99 °C and is stable to at least 130 °C and 60 kbar.…”

“…Oligoynes ( [ n ]1 ) are stable toward visible light, but 254 nm light excites butadiynes to a chemically reactive state . In crystals or ordered films, a string of butadiyne moieties on neighboring molecular rods can be oligomerized or polymerized into the corresponding trans- − or cis- polybutadiyne derivatives. − The occurrence of the polymerization and its course are determined by the mutual orientation of the butadiyne groups . End groups bulkier than hydrogen, such as tert -butyl, triethylsilyl, and phenyl, have an important stabilizing effect.…”

A Solid State Strategy for the Preparation of Carbon‐rich Polymers

“…It has often been proposed that these substituents will significantly enhance the nonlinear optical properties of the polymer [21][22][23]. However, until recently, few of these polydiacetylenes were known to exist [23][24][25].…”