The synthesis and characterization of two-photon fluorescent chromophores for biological imaging

Abstract

Two consequences of two-photon absorption phenomena (TPA); pin-point resolution and improved depth penetration, have generated interest in its potential use in biological imaging. Conventional dyes used for confocal scanning laser microscopy work well for this one-photon absorption process, however have not been optimized for two-photon absorption. Thus a need exists for the synthesis of two-photon fluorescent dyes with a large two-photon absorption cross sections. A variety of TPA dyes, of three classes were synthesized and characterized: (i) bis(styryl)benzene derivatives; (ii) amphiphilic dyes; (iii) cyanine-like dyes. In the design of these dyes, the structural features that affected two-photon cross section delta, and the fluorescence quantum yield phifl, were chosen and tuned with the aim of optimizing these parameters. With the cyanine-like derivatives, the effects of resonance enhancement and detuning were also factors that required optimization through structural alterations and modification.