Molecular modeling in dye chemistry: Studies involving two disperse dyes

The equilibrium geometries of C.I. Disperse Yellow 86 and C.I. Disperse Red 167 are predicted using semi-empirical and mechanical methods. All semi-em pirical geometry optimizations involve MNDO, MINDO/3, AM1, and PM3 Hamilton ians implemented in MOPAC, and CNDO and INDO Hamiltonians implemented in ZI NDO for self-consistent field energy calculations. MOPAC optimizations use a Broyden-Fletcher-Goldfarb-Shanno function minimizer, while ZINDO optimiza tions employ a Newton-Raphson search minimization technique. All semi-empir ical optimizations are initiated from an identical starting structure that has been optimized with an augmented MM2 mechanical forcefield in conjuncti on with a conjugate gradient minimizer algorithm, When the predicted struct ures of the two disperse dyes are compared to x-ray crystal structures, PM3 and AM1 give the best correlations between predicted and experimental valu es for atomic and hydrogen bond lengths. MINDO/3 gives the closest predicti ons of the improper torsion angle associated with aryl amino groups. PM3 an d, to a lesser extent, AM1 tend to distort planar aryl amino nitrogen atoms .