Abstract:

 A series of soluble 2,9,16,23-tetrasubstituted free-base phthalocyanines were synthesized and studied spectroscopically. The lowest electronic transition energy and the lowest excited singlet state energy of the phthalocyanines substituted with alkyl, alkoxy and aryloxy groups can be correlated well with the Hammett's meta-directing group effect. While the strong electron-withdrawing group (nitro) and the strong electron-donating group (amino) may induce intense intramolecular charge-transfer which results in the formation of aggregates, marked distortion of the absorption spectra and quenching of the excited states. However, all the substituents have less influence on the vibrational level.

Key words: Phthalocyanine, Charge-transfer, Aggregate, Hammett correlation