Fluorescent H-aggregates from a non-planar AlOHPc phthalocyanine in spin-coated film,

CURCIO, SERGIO FERNANDO

Congreso; Icoopma 2018; 2018

Phthalocyanines are well known for their tendency to undergo self-aggregation, which decreases their solubility and strongly affects their photophysical properties in undesirable ways [1]. The H-type aggregates, in particular, often referred to as face to face aggregates, have their absorption maxima blue shifted with respect to the monomer and in most cases are non-fluorescent [2-3]. Here, electronic absorptions, steady state and time resolved fluorescence studies of the Aluminum Phthalocyanine Hydroxide (AlOHPc) in highly diluted dimethylformamide (DMF) solution and spin-coated thin films (700 rpm, 1000 rpm, 2000 rpm, 3000 rpm, 4000 rpm, 5000 rpm and 6000 rpm) at room temperature are reported. The AlOHPc in DMF solution exhibits two well known main electronic absorption bands (Soret and Q band) typical of monomers of the phthalocyanines, with the more intense band (band Q) at 670 nm, and a emission band centered at 690 nm with a fluorescence lifetime of ∼9.0 ns. In solid thin film this compound forms fluorescent H-aggregates (or higher order aggregates), with an absorption Q band blue shifted to 644 nm and exhibits a red shifted emission band centered at 720 nm. Fluorescence lifetimes of the aggregated species exhibit shorter lifetimes with bi-exponential decay of 3.1~2.3 ns and 0.7~0.3 ns. The degree of AlOHPc aggregation in solid thin film has been related to the formation of aggregates via intermolecular interactions even with non-planarity of AlOHPc molecule due to the presence of hydroxy (OH) group.