Multi-branched Dyes Research Articles

Three-branched coumarin derivatives for two-photon uncaging. How does branching influence the efficacy?

In the design of non-linear optical chromophores, the conjugation pathways in multi-branched dyes are known to influence heavily their optical properties. Herein, we investigate this strategy for the design of two-photon (2P) responsive photolabile protecting groups (PPG) by assembling via a triphenylamine core extended coumarinylmethyl derivatives. The experimental study reveals an enhancement of the 2P absorption in the tri-branched compound, but a strikingly different photophysics behaviour resulting in a decrease in bond cleavage efficiency, and aggregation in aqueous acetonitrile. These combined effects results in much poorer 2P uncaging efficiency of the three-branched derivatives. In contrast, the corresponding mono-branched coumarin exhibit very high 2P photochemical efficiency (450 GM).

Change of Quadrupole Moment upon Excitation and Symmetry Breaking in Multibranched Donor-Acceptor Dyes.

Upon photoexcitation, a majority of quadrupolar dyes, developed for large two-photon absorption, undergo excited-state symmetry breaking (ES-SB) and behave as dipolar molecules. We investigate how the change of quadrupole moment upon S1 ←S0 excitation, ΔQ, influences the propensity of a dye to undergo ES-SB using a series of molecules with a A-π-D-π-A motif where D is the exceptionally electron-rich pyrrolo[3,2-b]pyrrole and A are accepting groups. Tuning of ΔQ is achieved by appending a secondary acceptor group, A', on both sides of the D core and ES-SB is monitored using a combination of time-resolved IR and broadband fluorescence spectroscopy. The results reveal a clear correlation between ΔQ and the tendency to undergo ES-SB. When A is a stronger acceptor than A', ES-SB occurs already in non-dipolar but quadrupolar solvents. When A and A' are identical, ES-SB is only partial even in highly dipolar solvents. When A is a weaker acceptor than A', the orientation of ΔQ changes, ES-SB is observed in dipolar solvents only and involves major redistribution of the excitation over the D-π-A and D-A' branches of the dye.

Two-photon absorption and cell imaging of two multi-branched dyes based on curcumin

Two novel multibranched dyes curcumin-based: 1,7-bis(4′-propyloxy-3′-methyloxy-phenyl)-3-propyloxy-5-carbonyl-1,6-heptadiene (dye 1) and 1,7-bis(4′-acetate ethyloxy-3′-methyloxy-phenyl)-1,6-heptadiene-4,4-diacetate ethyl-3,5-dione (dye 2) were easily prepared. Their one- and two-photon absorption properties have been investigated carefully. The two-photon absorption (TPA) cross sections measured by two-photon excited fluorescence (TPEF) were determined to be 1143 and 842 GM for dye 1 and dye 2, respectively. Cell viability tests revealed the as-prepared compounds possessed low cytotoxicity against MCF-7 cell lines over a period of at least 24 h. In addition, in vitro and in vivo studies demonstrated the dye 1 could enter into tumor cells, and even rapid accumulate in tumor tissues, which makes it an ideal organic material for biomedical imaging.

Facile pathways to multichromophoric arrays based on a truxene platform

Multi-branched dyes were synthesized using a truxene platform appropriately functionalized with iodo residues, the key step here being a controlled iodination process giving access to mono-, di-, tri- and hexa-derivatives. Conversion of the iodo compounds to the corresponding alkynes followed by cross-coupling with iodophenylindacenes catalysed by Pd(0) or with chloro-Pt(II) complexes catalysed by Cu(I) enabled the introduction of multiple chromophore/luminophore units. Both neutral and cationic species involving Pt(II) centres were obtained in excellent yields. Connection of ethynylpyrene units to boron within the hexa-grafted truxene Bodipys provided very efficient cascade singlet energy transfer from the pyrene to the yellow emitter. Irradiation in the truxene core also resulted in quantitative energy transfer to the organic dyes.

Synthesis of multi-branched dipyrromethene dyes with soluble diethynylphenyl links

Multi-branched dyes were prepared using a convergent step-by-step procedure. The key dibutoxydiethynylphenyl spacing units were first linked to a difluoroboradipyrromethene (yellow fluorophore) dye via the pseudo-meso position and then selectively cross-coupled to a di-(4-phenyliodo)ethynylborodiisoindolomethene (red emitter via the boron). When ethynylpyrene units were connected at the periphery to the boron of the yellow emitter, efficient cascade singlet energy transfer events occurred from the pyrene to the yellow and to the red emitters.

Novel Heteroaromatic‐Based Multi‐Branched Dyes with Enhanced Two‐Photon Absorption Activity

AbstractFor Abstract see ChemInform Abstract in Full Text.

Design and synthesis of heterocyclic multi-branched dyes for two-photon absorption

We report the first example of a heterocycle-based multi-branched two-photon absorption (TPA) dye. We show that the new chromophore presents a very large TPA cross-section in the femtoseconds (fs) regime. Comparison of the TPA cross-sections between the branched system and the corresponding “monomeric unit” shows a strong cooperative enhancement. A value of 22.6:1, corresponding to a 750% enhancement, was observed.

Novel heteroaromatic-based multi-branched dyes with enhanced two-photon absorption activityElectronic supplementary information (ESI) available: Experimental section. See http://www.rsc.org/suppdata/cc/b3/b305995b/

The first examples of heterocycle-based multi-branched dyes with efficient two-photon absorption (TPA) activity are reported; the novel chromophores exhibit large TPA cross sections (as high as 1600 x 10(-50) cm4 s photon(-1) molecule(-1), measured with 150 fs laser pulses at 800 nm); a strong cooperative enhancement in the branched systems with respect to the one-dimensional sub-units is found.