Design of a New Optical Material with Broad Spectrum Linear and Two-Photon Absorption and Solvatochromism

Abstract

A fluorene-bridged squaraine dimer (SD-FLU-SD) was designed with the purpose of combining various chromophores in one molecule and enhancing its two-photon absorption properties using intra-and interchromophore transitions. Linear and nonlinear absorption properties of SD-FLU-SD were investigated with the goals of understanding the nature of one-and two-photon absorption spectra, determining the molecular optical parameters, and performing modeling of the photophysical processes. The optical behavior of this new SD-FLU-SD "hybrid" molecule was compared with its separate squaraine constituent moiety. Linear spectroscopic characterization includes absorption, fluorescence, excitation and emission anisotropy, and quantum yield measurements in solvents of different polarity and viscosity. Spectral positions of the absorption−fluorescence peaks and quantum yields of SD-FLU-SD and its separate squaraine moiety exhibited complex and nontrivial behavior as a function of solvent polarity. Comprehensive study of this unusual solvatochromism was conducted and interpreted using various models. Nonlinear spectroscopic studies included two-photon absorption measurements using the femtosecond Z-scan technique. The two-photon absorption spectrum of SD-FLU-SD was broad, covering the spectral range from 800 to 1400 nm with a maximum two-photon absorption cross section of 2 750 GM (1 GM = 1 × 10 −50 cm 4 s/photon). Quantum chemical analysis, based on time-dependent density functional theory, agreed with the experimental data and revealed details on the energy-level structure and origin of the linear and nonlinear absorption behavior of this novel SD-FLU-SD compound. These investigations advance the understanding of the nature of electronic transitions and the structure−property relations in long conjugated molecules, which are important for the rational design of new organic optical materials.

Pyrrolo[3,2‐b]pyrroles—From Unprecedented Solvatofluorochromism to Two‐Photon Absorption

“…[24] It has to be emphasized that although a relaxed (symmetry broken) excited state is possible due to the interactions of the excited structure with solvents molecules, the quadrupolar charge distribution cannot induce a uniform reaction field at the location of the solute. The larger solvatofluorochromism compared to solvatochromism for centrosymmetric chromophore (which puts these compounds into class I chromophores according to Terenziani classification) can arise only from two phenomena: large change in electronic distribution [25] or symmetry breaking in the relaxed excited state. [23] In analogy to platinum complexes described by Cooper and co-workers [25a] the strongly electron-withdrawing nitro group acts as game-changer and it induces symmetry breaking in the S1 state.…”

“…The larger solvatofluorochromism compared to solvatochromism for centrosymmetric chromophore (which puts these compounds into class I chromophores according to Terenziani classification) can arise only from two phenomena: large change in electronic distribution [25] or symmetry breaking in the relaxed excited state. [23] In analogy to platinum complexes described by Cooper and co-workers [25a] the strongly electron-withdrawing nitro group acts as game-changer and it induces symmetry breaking in the S1 state.…”

Symmetry- and Solvent-Dependent Photophysics of Fluorenes Containing Donor and Acceptor Groups

“…[15][16][17][18] One particular class of compounds that has received significant attention in this area is fluorene-bridged derivatives. [19][20][21][22][23][24][25] These molecules are often designed as either symmetrical (D-π-D or A-π-A) or asymmetric (D-π-A) with the fluorene serving as the π-bridge. A number of functional donors (such as dimethylamino, diphenylamino, carbazoles, pyrroles, and dialkylamino) and acceptors (such as ketone, nitro, pyridine, and benzothiazole) have been explored.…”

Computer aided chemical design: using quantum chemical calculations to predict properties of a series of halochromic guaiazulene derivatives

“…To this end, the use of quantum chemical calculations to provide a prediction of a compound's properties prior to generating it in the laboratory could help to minimize waste generated by synthesis of impractical derivatives. The use of in silico techniques is commonly used to aid in the explanation of experimental results [2,3], though more recently studies have been directed towards identifying sustainable solvents [4], as well as designing solar cell components [5] and complex metal oxides [6]. …”