Dynamic-coupling alkyl-polarization model for the optical activity of the 175 nm absorption band of chiral diacetylenes

Abstract

The optical activity and dipole strength of the 170–175 nm ¹Σ⁺_g→¹Σ⁺_u transition of (S)-2,2,7,8,8-pentamethyl-nona-3,5-diyne can be accounted for, to a large extent, by an independent systems approach, where the allowed diacetylene transition is coupled to environmental alkyl-group polarizabilities. A chromophore point-dipole–environmental-dipole approximation accounts for only 14% of the observed rotational strength whilst an extended chromophore multipole–dipole model substantially reproduces the experimental value.