Polarization spectroscopy of aluminum phthalocyanine hydroxide embedded in superfluid helium droplets

We report electronic polarization spectroscopy of aluminum phthalocyanine hydroxide embedded in superfluid helium droplets orientated by a DC electric field. By monitoring the laser induced fluorescence as a function of the polarization direction of the excitation laser, we conclude that the transition dipole is predominantly perpendicular to the permanent dipole. Further quantitative analysis, however, shows that the angle between the transition dipole and permanent dipole is only 74°, and the out of plane component is about 8%. This result agrees with our previous conclusion on metal phthalocyanine chlorides. We suggest that this phenomenon might be related to the out of plane central metal atom, which could introduce a n–π∗ type transition.