Ian Ferguson

Quadratic non-linear optical properties of some donor–acceptor substituted thiophenes

A series of thiophenes and bithiophenes containing combinations of dimethylamino and dimethylhydrazono π-donor and nitro and dicyanovinyl π-acceptor groups was synthesized in order to study their non-linear optical properties. Solution molecular hyperpolarizabilities were determined by a combination of experimental dipole moments and results from the electric field induced second harmonic generation experiment. Values obtained correlate well with those calculated by the CNDOVSB molecular orbital method. The main structure-property relationships deduced from the results are: (i) thiophene provides a more efficient electron delocalization pathway than benzene; (ii) this increase is proportionately even greater for bithiophene compared with biphenyl; (iii) dimethylhydrazono results in twice the hyperpolarizability of dimethylamino in a comparable molecule; and (iv) dicyanovinyl is a more effective electron acceptor group than nitro in the thiophenes synthesized and calculated.

The regio- and stereochemistry of the alkoxide-induced ring-opening of methoxymethylidene-substituted homopthalic anhydride

Abstract Ring-opening of methoxymethylidene-substituted homophthalic anhydride (1) by methoxide occurs by two modes. Attack at the 1-position (“benzoate” carbonyl) leads to a stable acid-ester. A combination of unambiguous syntheses and 1H- and 13C-n.m.r. spectroscopy has been used to show that this material has the “benzoate ester, acrylic acid” structure (5). This corrects the structure assignment given earlier for this material, which incorrectly concluded “benzoic acid, acrylate ester”, (2). Compound (2), resulting from attack at the “acrylate” carbonyl, is a co-product of (5), but is unstable. It recyclises in an alternative fashion to give (dihydro)isocoumarin-type products (15) and (16).

Non-linear Optical Properties of Squarate Esters and Amides†

In agreement with theoretical prediction, a squaric acid diamide shows appreciable quadratic non-linear optical (NLO) activity in solution, and because of their transparency such amides may be attractive materials for second harmonic generation of blue light, although all crystalline derivatives measured were essentially NLO inactive.