Synthesis, Characterization, and Optical Properties of New Two-Photon-Absorbing Fluorene Derivatives

Abstract

The synthesis of a series of four new compounds containing fluorenyl chromophores is presented, along with the results of spectroscopic and photochemical studies aimed at understanding the two-photon absorption properties and energetics of their electronically excited states. The molecular structures of the compounds were systematically varied to allow comparison of molecules possessing high and low molecular symmetry, short and long alkyl chains, and a fluorenyl conjugated π-system. Solvent-dependent absorption and emission were investigated along with π-conjugation length. Preliminary measurements of two-photon absorption (2PA) using a two-photon fluorescence method indicate that these chromophores exhibit high two-photon absorptivity. A symmetrical molecule (3), possessing a relatively large π-conjugated system, flanked on either side by electron-withdrawing groups (benzothiazole), exhibited a peak 2PA cross section (δ) of 6000 × 10 -50 cm 4 s photon -1 molecule -1 at 600 nm. Excitation anisotropy studies revealed the position of the S 0 f S 1 and S 0 f S 2 electronic transitions. Consistent with quantum mechanical selection rules, the two-photon allowed transition (S 0 f S 2 ) was dominant.

Two-photon absorption spectra of carotenoids compounds

“…8 In the last decade, p-conjugated molecules have emerged as potential candidates for applications in photonic devices due to its easy handling, environmental stability and structural flexibility. 9,10 Among these materials, carotenoids constitute an important class of linear p-conjugated molecules that exhibit high degree of electronic delocalization and ultrafast dynamics. [11][12][13] b-carotene, for example, has an important role in the light-harvesting function of bacterial photosynthesis; 14,15 all-trans retinal (analog to trans-b-apo-8 0 -carotenal) is responsible for light transduction in nervous impulses, which involves a series of biochemical events in bacteriorhodopsin.…”

Theory and computations of two-photon absorbing photochromic chromophores

“…A types with the aim of increasing 2PA absorption cross-sections [118][119][120][121][122][123]. However, the choice of functional groups and linkages, the most appropriate for developing chromophores with large 2PA characteristics, is still under active investigation [124][125][126][127][128][129][130][131][132][133][134][135].…”

Predictions of Two Photon Absorption Profiles Using Time-Dependent Density Functional Theory Combined with SOS and CEO Formalisms

“…In recent studies fluorene derivatives have been extended to D-π-π-A and A-π-π-A types with the aim of increasing 2PA absorption cross-sections [6][7][8][9][10]. However, the choice of functional groups and linkages the most appropriate for developing chromophores with the largest 2PA characteristics it is still under active investigation.…”