Controlling Two-Photon Action Cross Section by Changing a Single Heteroatom Position in Fluorescent Dyes

Abstract

The optimization of nonlinear optical properties for “real-life” applications remains a key challenge for both experimental and theoretical approaches. In particular, for two-photon processes, maximizing the two-photon action cross section (TPACS), the figure of merit for two-photon bioimaging spectroscopy, requires simultaneously controlling all its components. In the present Letter, a series of difluoroborates presenting various heterocyclic rings as an electron acceptor have been synthesized and their absorption, fluorescence, photoisomerization, and two-photon absorption features have been analyzed using both experimental and theoretical approaches. Our results demonstrate that the TPACS values can be fine-tuned by changing the position of a single heteroatom, which alters the fluorescence quantum yields without changing the intrinsic two-photon absorption cross section. This approach offers a new strategy for optimizing TPACS.

In Silico Screening of Two‐Photon Absorption Properties of a Large Set of Bis‐Difluoroborate Dyes

“…Additionally, the presence of BF 2 ‐group also increases significantly 2PA cross‐section as demonstrated by comparisons between BF 2 ‐dyes and its precursor [51] . Moreover, the 2PA properties of BF 2 ‐containing dyes can be tuned by various synthetic strategies [52,53] . For the purpose of the present study we designed three different series of dyes ( A , B , and C see Figure 1) containing the difluoroborate electron‐withdrawing moiety.…”

“…[51] Moreover, the 2PA properties of BF 2 -containing dyes can be tuned by various synthetic strategies. [52,53] For the purpose of the present study we designed three different series of dyes (A, B, and C see Figure 1) containing the difluoroborate electronwithdrawing moiety. Previously, some of us showed that structure similar to series A might yield quite large s 2PA .…”

“…We note that this position is synthetically preferable to the corresponding position 5 close to the left hand-side arm carrying R substituent. The studied compounds are derivatives of amides and their use in BF 2 -complexation is welldescribed, [52,55,56] while the elongation of the linkers may be achieved through Wittig reaction that was already applied in similar cases. [55] We of course do not state here that all 280 compounds treated here would be straightforward to synthesize, just that the dye design is fulfilling some realism.…”

Two-Photon Absorption: An Open Door to the NIR-II Biological Window?

“…In order to visualise, characterise and quantify biological entities, bright molecular imaging probes are needed (Yang et al, 2020a). To generate bright 2P microscopy images without causing considerable photo-damage to the sample at laser intensities required (1 GW•cm −2 at the focal plane; or ~5 mW at the objective lens), it is estimated that the 2P brightness σ 2 Φ f of the imaging agent should be more than 50 GM (Kim and Cho, 2015;Osmialowski et al, 2020). As such, breaking down the barriers to exploit NIR-II wavelengths in 2P bio-imaging involves three main challenges: (i) shifting the 2PA band of the imaging agent beyond 1000 nm, which typically involves 1PA above 500 nm; (ii) improving the 2PA crosssection σ 2 above this wavelength, typically to values >50-100 GM; and (iii) retaining a high enough fluorescence quantum yield Φ f to image tissues with high contrast.…”

Aromatic Amines in Organic Synthesis. Part II. p-Aminocinnamaldehydes

“…They have been studied for applications in various areas of photochemistry due to their structure versatility and facile modifications for electron-donating abilities [ 11 , 12 , 13 ]. In general, organic compounds bearing an alkylamino group may be synthesized through a related synthetic strategy using one of the following: Heck reaction [ 14 ], Knoevenagel condensation [ 13 , 15 ], Wittig reaction [ 16 ], Suzuki-Miyaura cross-coupling reaction [ 17 ] and several different reagents, such as aryl bromides with amino substituents [ 14 ], p -aminobenzaldehydes [ 13 , 15 ] and p -aminobenzoic acid derivatives [ 18 , 19 ].…”