INTERMOLECULAR INTERACTION BETWEEN SQUARYLIUM CYANINE AND PORPHYRIN

In this paper, the interaction between squarylium cyanine and porphyri n in chloroform is investigated by absorption and fluorescence spectro scopy. Emphasis has been put on the mechanism of intermolecular energy transfer. The overlap integral J between the absorption spectrum of s quarylium cyanine and the fluorescence spectrum of porphyrin was calcu lated, which reveals that the singlet-singlet energy transfer may occu r from porphyrin to squarylium cyanine in solution. In comparison of t he observed rate constant [k(q)(II)=6.1x10(13) (mol/L)(-1).s(-1)] for fluorescence quenching of porphyrin by squarylium cyanine with the dif fusion rate constant in chloroform [k(dif) =1.1 x 10(10) (mol/L)(-1).s (-1)] and the rate of energy transfer [k(et)less than or equal to 6.7x 10(4) (mol/L)(-1).s(-1) in the experimentally dilute solutions] estima ted from Forster formula, the possibility of energy transfer by electr on exchange or/and coulombic mechanism could be excluded. So it has be en definitely convinced that the intermolecular energy transfer betwee n them is performed through long-distance radiative mechanism which is in good agreement with the results in experimentally dilute concentra tion (<10(-4) mol/L). Meanwhile, the fluorescence of squarylium cyanin e can also be quenched by porphyrin, which suggests that photoinduced charge transfer with other process may occur. In the contrast, the res ults can be partly contributed to understand the reason why the energy transfer efficiencies of porphyrin phi(et)(II) are always lower than its fluorescence quenching efficiencies phi(q)(I).