Determination of the ground state, excited state and change in dipole moments of magnesium and zinc chlorin

Abstract

High-resolution Stark effect measurements on the S 1←S 0 (ππ*) origin of magnesium chlorin (MgCh) and zinc chlorin (ZnCh) in single crystals of n-octane at 4.2 K are reported. The corresponding change in dipole moment (∣Δ μ ge∣) associated with each transition was estimated to be 0.23±0.04 and 0.27±0.05 debye, respectively. Each molecule's orientation in the n-octane crystal was also determined. The change in dipole moment of MgCh was also found using solvatochromic shift data (∣Δ μ ge∣=0.33±0.08 debye). The ground state dipole moment ( μ g) of MgCh was determined by dielectric constant measurement of MgCh/benzene solutions ( μ g=2.26±0.08 debye). These were combined to calculate the average excited state dipole moment of MgCh ( μ e=2.51±0.08 debye). The ground state dipole moment of ZnCh was also determined using solvatochromic shift data ( μ g=3.17±0.08 debye). This was combined with its measured ∣Δ μ ge∣ to calculate the excited state dipole moment of ZnCh ( μ e=3.44±0.08 debye); the S 1←S 0 (ππ*) origin band of both complexes was red-shifted at room temperature as the polarity of the solvents was increased, which implies that Δ μ ge is positive.