Site selective optical spectra of free base porphin in anthracene

The low temperature optical spectra of free base porphin in crystalline anthracene have been observed in the visible region of the spectrum. Quasilines and broad components were observed in the region of the forbidden Q bands. Site selection techniques were used to separate the spectra of inequivalent site species, and vibronic frequencies were assigned in the ground state and excited Q states. The relative strengths of the broad and quasiline components of the spectra in the Q_x and Q_y states indicated that the host lattice may affect the relative transition strengths of Q_x and Q_y. These results indicated that the strength of the transition to Q_x is greater than that of Q_y for a free porphin molecule.