PHOTOPHYSICS OF LITHIUM PHTHALOCYANINES AND THEIR RADICALS

The photophysical properties of dilithium phthalocyanine (Li2PC), dilithium naphthalocyanine (Li2NPc), and their corresponding stable radicals have been measured in both their ground and excited states. The S1 lifetimes of Li2Pc and Li2NPc are 5.3 and 4.4 ns, respectively. The transient absorption spectra of S1 show maxima at 478 nm for Li2Pc and 520 nm for Li2NPc with differential molar absorption coefficients of 14 200 and 28 900 M-1 cm-1, respectively. The fluorescence quantum yield is the same (0.5 +/- 0.05) for both molecules. The T1 lifetimes are >60 mus for Li2Pc and >100 mus for Li2NPc. The triplet quantum yield times the differential triplet molar absorption coefficients are 3800 M-1 cm-1 at 469 nm for Li2Pc and 9500 M-1 cm-1 at 603 nm for Li2NPc. Li2Pc and Li2NPc will photoionize biphotonically upon excitation at 354 nm to give the corresponding stable radical phthalocyanines. The excited state of LiPc. is also reported and it has a 130-ps lifetime.