Design, Synthesis, and Structural and Spectroscopic Studies of Push–Pull Two-Photon Absorbing Chromophores with Acceptor Groups of Varying Strength

Abstract

A new series of unsymmetrical diphenylaminofluorene-based chromophores with various strong π-electron acceptors were synthesized and fully characterized. The systematic alteration of the structural design facilitated the investigation of effects such as molecular symmetry and strength of electron-donating and/or withdrawing termini have on optical nonlinearity. In order to determine the electronic and geometrical properties of the novel compounds, a thorough investigation was carried out by a combination of linear and nonlinear spectroscopic techniques, single crystal X-ray diffraction, and quantum chemical calculations. Finally, on the basis of two-photon absorption (2PA) cross sections, the general trend for π -electron accepting ability, i.e., ability to accept charge transfer from diphenylamine was: 2-pyran-4-ylidene malononitrile (pyranone) > dicyanovinyl > bis(dicyanomethylidene)indane > 1-(thiophen-2-yl)propenone > dicyanoethylenyl > 3-(thiophen-2-yl)propenone. An analog with the 2-pyran-4-ylidene malononitrile acceptor group exhibited a nearly three-fold enhancement of the 2PA< δ (1650 GM at 840 nm), relative to other members of the series.

RGD-conjugated two-photon absorbing near-IR emitting fluorescent probes for tumor vasculature imaging

“…Excitation in the main absorption band resulted in a fluorescence signal that displayed a distinct solvatochromic pattern (Figure 1, A): λ max underwent a bathochromic shift, the peak broadened, and the quantum yield of the fluorescence decreased with increasing polarity (Table 1). These results are comparable to a hydrophobic analogue previously reported; 20 the decreased fluorescence quantum yield is a likely result of the increased flexibility rotational propensity of the pendant chains in the 9-position of the fluorene moiety.…”

D‐π‐A Conjugated Molecules for Optoelectronic Applications

“…Belfield et al have investigated fluorene‐based dipolar chromophores with several electron acceptors for enhancing the σ 2PA values . Electron accepting groups included dicyanovinyl, dicyanoethylenyl, 2‐pyran‐4‐ylidene malononitrile, and bis(dicyanomethylidene)indane.…”

A two-photon ratiometric fluorescence probe for Cupric Ions in Live Cells and Tissues

“…However, most of these probes have been evaluated using one-photon microscopy and require relatively short excitation wavelengths, limiting their use in deep-tissue imaging because of the shallow penetration depth (<80 μm). To determine Cu 2+ deep inside living tissues, it is crucial to use two-photon microscopy (TPM), a new technique that utilizes near-IR two-photon excitation21222324252627282930. TPM offers several advantages such as larger imaging depth (>500 μm), minimized autofluorescence background, and less photodamage associated with the use of near infrared excitation.…”