Special features of spectral and luminescent properties of squarilic dyes in polymer matrices

A study was made of spectral and luminescent properties of a squarilic dye on the basis of 1,3,3-trimethyl-3H-indoline in comparison with the cationic polymethine dye representing a derivative of the same heterocycle. The squarilic dye was introduced into polymer films of poly-N-epoxypropylcarbazole, which is capable of bearing photoproduced charges, and polystyrene, which lacks this ability. Luminescence spectra of films with different dye concentrations at temperatures of 4.2 and 300 K were studied. Spectral and luminescent properties of squarain in both types of polymers were found to be determined by the dye tendency to aggregation. For poly-N-epoxypropylcarbazole, this tendency is less pronounced than for polystyrene, which is associated with the enhancement of specific solvation of a bipolar squarain molecule by polar groups of poly-N-epoxypropylcarbazole. The structure with an angle between chromophore directions of 180° is shown to be the most likely spatial structure of associates. The advantage of this structure is that it is stabilized at both ends of bipolar molecules by electrostatic attractive forces between opposite charges.