Chemical Physics Letters vol:225 issue:4-6 pages:398-403
Irradiation of the monomeric phthalocyanine HexSiO(SiPc)OSiHex3 isolated in an Ar matrix at T = 13 K with the 632.8 nm line of a He/Ne laser produces a resonant spectral hole in the vibrational sideband located about 700 cm-1 above the origin of the Q band. This hole is accompanied by several sideholes in the origin region. These permit a precise determination of several excited-state vibrational frequencies. For dimeric Hex3SiO(SiPC-O-SiPc)OSiHex3 in the same matrix the changes in the absorption spectra after irradiation into the Q band reveal an out-of-plane polarization of the bands which are not present in the monomer absorption. This points to substantial charge-resonance contributions to the excitonic coupling between the two SiPc units in dimeric Hex3SiO(SiPc-O-SiPc)OSiHex3.