FLUORESCENCE OF PHTHALOCYANINES - EMISSION FROM AN UPPER EXCITED-STATE

The weak (PHI(f) < 10(-3)) fluorescence at around 430 nm of the S2 upper excited singlet state of metal-free phthalocyanine and metallophthalocyanines is presented. Polarization measurements indicate that the emission is short-lived (< 800 ps) contrary to the intense (PHI(f) > 0.3) normal emission at around 700 nm originating from S1 and having a lifetime in the 4.1 to 10.6 ns range, depending on the solvent. The short wavelength emitting S2 excited state has been populated by a two photon absorption process using the excitation light at 695 nm of a pulsed ruby laser This process is shown not to involve the triplet state but the following stepwise two photon absorption process. S(o) --> (hv) S1 --> (hv) S(n) --> S2.