PHOTOCHEMISTRY OF SQUARAINE DYES - EXCITED TRIPLET-STATE AND REDOX PROPERTIES OF CROWN-ETHER SQUARAINES

The excited state and redox properties of three crown-ether derivative s of squaraines have been studied. Direct laser excitation of these dy es leads to the formation of excited triplets, dye radical cations and anions, via a biphotonic photoionization mechanism. All these transie nt species absorb strongly in the visible region. The triplet states o f these dyes generated via triplet-triplet energy transfer from 3(1-py renecarboxaldehyde) and C-3(60)* photosensitizers also produce dye ra dical cations and anions via a self-quenching process. The bimolecular rate constants for the self-quenching process are in the range of (0. 5-1.9) x 10(9) M(-1) s(-1). The redox properties of these dyes have be en investigated by electrochemical, spectroelectrochemical, and radiol ytic methods. They exhibit two reversible oxidations in the potential range of 0.7-1.2 V vs SCE. The spectral features of electrochemically generated one electron oxidation product (lambda(max) = 680 nm) match those of dye radical cations produced by photochemical and radiolytic methods.