Two-photon absorption properties of cationic 1,4-Bis(styryl)benzene derivative and its inclusion complexes with cyclodextrins

Two-photon absorption properties of 1,4-bis{4′-[N,N-bis(6″- trimethylammoniumhexyl)amino]styryl}benzene tetrabromide (C1) and its inclusion complexes (ICs) with cyclodextrins (CDs) have been studied. Upon complexation with CDs, the absorption spectra of C1 showed a slight red shift, whereas the emission spectra showed a blue shift with concomitant increase in the fluorescence quantum efficiency. A Stern-Volmer study using K ₃Fe(CN)₆ as a quencher revealed significant reduction in the photoinduced charge transfer quenching, in accord with the IC formation. Comparison of the spectroscopic results reveals that C1 forms increasingly more stable ICs in the order C1/β-CD < C1/γ-CD < C1/(3γ:β)-CD (γ-CD/β-CD 3:1, mole ratio). Moreover, the two-photon action cross section of C1 increased from 200 GM for C1 to 400 GM for C1/β-CD, 460 GM for C1/γ-CD, and 650 GM for C1/(3γ:β)-CD, respectively. Furthermore, the two-photon microscopy images of HeLa cells stained with C1 emitted strong two-photon excited fluorescence in the plasma membrane. These results provide a useful guideline for the development of efficient two-photon materials for bioimaging applications.