Two-photon fluorescence properties of novel quadrupolar and octupolar molecules

Using a wavelength-tunable optical parametric oscillation (OPO) laser, we investigate the two-photon fluorescence (TPF) properties of two quadrupolar (P2SS2Ph and PSS2PhNp) and three octupolar (P3SPh, P3SS2Ph and TRZ-Ph-Tol) donor-acceptor-donor (D-A-D) type molecules. TPF cross-section /spl delta/ of all the samples lies at the wavelength between 740 nm and 990 nm. Even though P3SS2PH octupolar and P2SS2PH quadrupolar molecules have distinctly different structures and symmetries, their maximum /spl delta/ are close. On the other hand, the maximum /spl delta/ of octupolar TRZ-Ph-Tol is very much larger than that of the structurally different octupolar P3SPh The /spl pi/-electron delocalization in TRZ-Ph-Tol is more extended than in P3SPh. It is thus tempting to conclude that the longer the conjugation length, the larger the maximum /spl delta/. Although the conjugation system of P3SS2Ph is no less extended, compared with TRZ-Ph-Tol, its /spl delta/ is much smaller. This may be due to the weaker central acceptor of P3SS2Ph. Furthermore, we investigate the /spl delta/ spectral difference between octupolar and quadrupolar molecules.