Two-Photon Absorption by Fluorene Derivatives: Systematic Molecular Design

Abstract

In this article, we employ a systematic approach to the computational quantum chemical study of the twophoton absorption (2PA) properties of 161 representative molecules containing a symmetrically substituted fluorene unit. The molecules studied contain meta-or para-substituted phenyl groups, five-and six-membered heterocycles, and benzo derivatives of five-membered heterocycles. The computational procedure employed to calculate the 2PA parameters was previously described [Chem. Mater. 2008, 20, 4142] and is based on semiempirical electronic structure methods: the RM1 model to optimize the molecular geometry and the INDO/S method to calculate the spectroscopic properties of the molecules. We further advance a new, simplified expression employed to calculate an approximate three-level contribution of the imaginary part of the negative component of the second hyperpolarizability. We then show that, in order to rationalize the 2PA cross sections for the substituted fluorenes, the three-level approximation has to be adapted to include a fourth state. That done, we advance that the parameter most responsible for the large observed variation in the calculated values of the 2PA cross sections for the substituted fluorenes is the effective transition dipole moment between the 1PA-active state and the two 2PA-active states. Based on our results, we discuss three structural effects that can contribute to the value of the 2PA cross section and show how they can be tuned. We conclude by propositioning novel putative molecules with potentially large values of 2PA cross sections, such as 2,2′-(9,9-dialkyl-9H-fluorene-2,7-diyl)dibenzo [d]oxazole.

Tricolor Luminescence Switching by Thermal and Mechanical Stimuli in the Crystal Polymorphs of Pyridyl‐substituted Fluorene

“…Figure 1b presents ac omparison of the emission spectra of MFDP in THF,c rystal V-MFDP,B -MFDP and G-MFDP.T he four emission spectra exhibited very different profiles and emission peaks ranging from 377 nm to 515 nm. On the basis of the reference, [51] we think that the emission of the THF solution peakeda t3 77 nm with av ibronic structure should originate from as ingle molecule of MFDP.O bviously,t he luminescence properties of the three crystal polymorphs are strictly related to their intermoleculari nteractions and molecular packingp atterns. In addition, compared with the three crystal polymorphs, the THFs olution of MFDP shows as hort fluorescence decay time (t ave = 0.23 ns), which should be attributed to the free MFDP single molecule ( Figure 1c).…”

Synthesis, crystal structures, and two-photon absorption of a series of cyanoacetic acid triphenylamine derivatives

“…After removing the solvent, the residue was purified by column chromatography using silica gel and petroleum ether/ethyl acetate (5/1; v/v) mixed as the eluent to give the yellow oil of CN3 (Yield: 56.6%). 1 …”

“…1 6, 155.3, 153.6, 148.7, 142.6, 139.3, 131.9, 131.3, 129.7, 128.0, 127.8, 127.0, 126.5, 123.9, 118.4, 116.5, 115.4, 101.6, 63.14, 14.66 …”

“…The two-photon absorption (2PA) process has selection rules that are different from those of the traditional one-photon absorption (1PA) processes [1], 2PA is quadratically proportional to the intensity of the incident light, and hence, by focusing the long wavelength laser beam, one can precisely localize 2PA in a small volume, and penetrate deep inside the bulk of the material. These merits of 2PA materials endow their promising applications, such as manufacturing of optical limiting, 3-D microfabrication, photodynamic therapy, high-density optical storage, holographic data storage, frequency-upconverted lasing, and bioimaging [2].…”

“…Accordingly, to address the practical application requirements for two-photon absorption materials, this idea is based on the following considerations: (1) Triphenylamine is a unique molecule possessing useful functions such as redox activity, fluorescence due to the high oxidizability of the nitrogen center, and transportability of positive charge centers via the radical cation species. So the family of triphenylamine derivatives was widespread use as hole transporting materials, emitting layers in electroluminescent diodes, light harvesters in dye-sensitized solar cells, and nonlinear optical materials during the past few decades [14]; (2) The ethoxyl segment, compared to a phenyl group, has much more steric hindrance and hence might avoid p-p stack between the molecules and more powerfully prevent unfavorable chromophore aggregation.…”