Tailored thioxanthone‐based photoinitiators for two‐photon‐controllable polymerization and nanolithographic printing

Printing of high‐resolution three‐dimensional nanostructures utilizing two‐photon polymerization has gained significant attention recently. In particular, isopropyl thioxanthone (ITX) has been implemented as a photoinitiator due to its capability of initiating and depleting polymerization on demand, but new photoinitiating materials are still needed in order to reduce the power requirements for the high‐throughput creation of 3D structures. To address this point, a suite of new thioxanthone‐based photoinitiators were synthesized and characterized. Then two‐photon polymerization was performed using the most promising photoinitiating molecule. Importantly, one of the initiators, 2,7‐bis[(4‐(dimethylamino)phenyl ethynyl)‐9H‐thioxanthen‐9‐one] (BDAPT), showed a fivefold improvement in the writing threshold over the commonly used ITX molecule. To elucidate the fundamental mechanism, the excitation and inhibition behavior of the BDAPT molecule were evaluated using density functional theory (DFT) calculations, low‐temperature phosphorescence spectroscopy, ultra‐fast transient absorption spectroscopy, and the two‐photon Z‐scan spectroscopic technique. The improved polymerization threshold of this new photoinitiator presents a clear pathway for the modification of photoinitiators in 3D nanoprinting. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1462–1475     

Synthesis and structure‐activity relationship of several aromatic ketone‐based two‐photon initiators

Several novel aromatic ketone‐based two‐photon initiators containing triple bonds and dialkylamino groups were synthesized and the structure‐activity relationships were evaluated. Branched alkyl chains were used at the terminal donor groups to improve the solubility in the multifunctional monomers. Because of the long conjugation length and good coplanarity, the evaluated initiators showed large two‐photon cross section values, while their fluorescence lifetimes and quantum yields strongly depend on the solvent polarity. All novel initiators exhibited high activity in terms of two‐photon‐induced microfabrication. This is especially true for fluorenone‐based derivatives, which displayed much broader processing windows than well‐known highly active initiators from the literature and commercially available initiators. While the new photoinitiators gave high reactivity in two‐photon‐induced photopolymerization at concentration as low as 0.1% wt, these compounds are surprisingly stable under one photon condition and nearly no photo initiation activity was found in classical photo DSC experiment. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis,structure and nonlinear optical properties of two novel two-photon absorption chromophores

Two triphenylamine-based derivatives that can be used as two-photon absorption chromophore,tris{4-[4-(3-trifluoromethyl-3-oxopanoyl)]phenyl}amine (1) and tris{4-[4-(3-phenyl-3-oxopanoyl)] phenyl} amine (2) were successfully synthesized and fully characterized by elemental analysis,IR,1H NMR and MS. The single crystal X-ray diffraction analysis showed that the molecules possess D-(π-A)3 structures. One-and two-photon absorption and fluorescence in various solvents were experimentally investigated. A data rec...     

Synthesis,Photophysical Properties of Tribranched Chromophores Based on 1,3,5‐Triazine Core and Different Electro‐donating End‐groups

Three two‐photon absorption (TPA) tribranched chromophores were successfully prepared, in which 1,3,5‐triazine is been as electron deficient core, 1,4‐phenylenedivinylene as conjugated bridge, 3,4‐ethylenedioxythiophene (EDOT) ( T1 ), N‐methylpyrrole ( T2 ) or triphenylamine ( T3 ) as electron‐donating end‐groups. Their photophysical properties were studied by absorption, one‐ and two‐photon fluorescence and TPA cross‐section determination. The nonlinear transmission (NLT) measurement in femtoseconds (fs) regime at 800 nm indicates that TPA cross‐section (₂ values of T1 , T2 and T3 with extended Π‐conjugated bridge are much larger than the corresponding chromophore T4 with a short length bridge, and TPA cross‐section of T1 with end‐groups EDOT exhibits a remarkable enhancement compared with T2 and T3 having the same length Π‐system. The chromophores T1 , T2 and T3 show also remarkable up‐converted luminescence and optical limiting activity.     

Three‐dimensional microfabrication of protein hydrogels via two‐photon‐excited thiol‐vinyl ester photopolymerization

Engineering three‐dimensional (3D) hydrogels with well‐defined architectures has become increasingly important for tissue engineering and basic research in biomaterials science. To fabricate 3D hydrogels with (sub)cellular‐scale features, two‐photon polymerization (2PP) shows great promise although the technique is limited by the selection of appropriate hydrogel precursors. In this study, we report the synthesis of gelatin hydrolysate vinyl esters (GH‐VE) and its copolymerization with reduced derivatives of bovine serum albumin (acting as macrothiols). Photorheology of the thiol‐ene copolymerization shows a much more rapid onset of polymerization and a higher end modulus in reference to neat GH‐VE. This allowed 2PP to provide well‐defined and stable hydrogel microstructures. Efficiency of the radical‐mediated thiol‐vinyl ester photopolymerization allows high 2PP writing speed (as high as 50 mm s^?1) with low laser power (as low as 20 mW). MTT assays indicate negligible cytotoxicities of the GH‐VE macromers and of the thiol‐ene hydrogel pellets. Osteosarcoma cells seeded onto GH‐VE/BSA hydrogels with different macromer relative ratios showed a preference for hydrogels with higher percentage of GH‐VE. This can be attributed both to a favorable modulus and preferable protein environment since gelatin favors cell adhesion and albumin incurs nonspecific binding. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4799–4810     

Chiral thiophene derivatives with optimal two‐photon absorption in near‐infrared window I and II

Thiophene derivatives are outstanding organic materials due to their wide spectral response, superior optoelectronic properties, and excellent environmental stability, which have attracted widespread attention in both theory and applications. However, their chiral analogues and corresponding chiroptical behaviors have been rarely investigated. Herein, a series of chiral thiophene derivatives are firstly designed by taking both optical chirality and two‐photon absorption (TPA) response into consideration, and are then investigated by modern analytical response theory. The calculated results demonstrate that these novel chiral thiophene derivatives show optimal TPA in the near‐infrared (NIR) window I and II, indicating that they are promising for biological applications. More importantly, they exhibit reasonable two‐photon circular dichroism (TPCD) signals, which are desirable candidates for chiral recognition regions. Furthermore, the calculations of orbital transitions shed light on that the intramolecular charge transfer plays an important role in their excellent TPA and TPCD behaviors in NIR regions.     

Synthesis and two‐photon absorption properties of conjugated polymers with N‐arylpyrrole as conjugated bridge and isolation moieties

Three novel conjugated polymers with N‐arylpyrrole as the conjugated bridge were designed and synthesized, which emitted strong one‐ or two‐photon excitation fluorescence in dilute tetrahydrofuran (THF) solution with high quantum yields. The maximal two‐photon absorption (TPA) cross‐sections of the polymers, measured by the two‐photon‐induced fluorescence method using femtosecond laser pulses in THF, were 752, 1114, and 1869 GM, respectively, indicating that the insertion of electron‐donating or electron‐withdrawing moieties into the polymer backbone could benefit to the increase of the TPA cross‐section. Their large TPA cross‐sections, coupled with the relatively high emission quantum yields, made these conjugated polymers attractive for practical applications, especially two‐photon excited fluorescence. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Refractive index‐modulated grating in two‐mode planar polymeric waveguide produced by two‐photon polymerization

A polymeric waveguide film was manufactured by spinning the materials on quartz substrate. Two‐photon‐initiated photopolymerization was carried out by tight‐focusing femtosecond laser pulses in the two‐mode planar waveguide. A typical index‐modulated grating of 2.5 × 2 mm areas without morphology was fabricated. The results show that peak‐to‐peak modulation depth of the surface profile of grating region was only about 7 nm. The diffraction efficiency (DE) of the grating with a spacing period 2 µm was 0.17% and the corresponding index modulation reached 5.7 × 10^?3. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis,one‐ and two‐photon properties of poly[9,10‐bis(3,4‐bis(2‐ethylhexyl‐oxy)phenyl)‐2,6‐anthracenevinylene‐alt‐N‐octyl‐3,6‐/2,7‐carbazolevinylene]

The synthesis, one‐ and two‐photon absorption (TPA) and emission properties of two novel 2,6‐anthracenevinylene‐based copolymers, poly[9,10‐bis(3,4‐bis(2‐ethylhexyloxy)phenyl)‐2,6‐anthracenevinylene‐alt‐N‐octyl‐3,6‐carbazolevinyl‐ene] ( P1 ) and poly[9,10‐bis(3,4‐bis(2‐ethylhexyloxy)phenyl)‐2,6‐anthracenevinyl‐ene‐alt‐N‐octyl‐2,7‐carbazolevinylene] ( P2 ) were reported. The as‐synthesized polymers have the number‐average molecular weights of 1.56 × 10⁴ for P1 and 1.85 × 10⁴ g mol^?1 for P2 and are readily soluble in common organic solvents. They emit strong bluish‐green one‐ and two‐photon excitation fluorescence in dilute toluene solution (? _P1 = 0.85, ? _P2 = 0.78, λ_em( P1 ) = 491 nm, λ_em( P2 ) = 483 nm). The maximal TPA cross‐sections of P1 and P2 measured by the two‐photon‐induced fluorescence method using femtosecond laser pulses in toluene are 840 and 490 GM per repeating unit, respectively, which are obviously larger than that (210 GM) of poly[9,10‐bis‐(3,4‐bis(2‐ethylhexyloxy) phenyl)‐2,6‐anthracenevinylene], indicating that the poly(2,6‐anthracenevinylene) derivatives with large TPA cross‐sections can be obtained by inserting electron‐donating moieties into the polymer backbone. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 463–470, 2010     

Concise Synthesis and Two‐Photon‐Excited Deep‐Blue Emission of 1,8‐Diazapyrenes

Efficient violet–blue‐emitting molecules are especially useful for applications in full‐color displays, solid‐state lighting, as well as in two‐photon absorption (TPA) excited frequency‐upconverted violet–blue lasing. However, the reported violet–blue‐emitting molecules generally possess small TPA cross sections. In this work, new 1,8‐diazapyrenes derivatives 3 with blue two‐photon‐excited fluorescence emission were concisely synthesized by the coupling reaction of readily available 1,4‐naphthoquinone O,O‐diacetyl dioxime ( 1 ) with internal alkynes 2 under the [{RhCl₂Cp*}₂]–Cu(OAc)₂ (Cp*=pentamethylcyclopentadienyl ligand) bimetallic catalytic system. Elongation of the π‐conjugated length of 1,8‐diazapyrenes 3 led to the increase of TPA cross sections without the expense of a redshift of the emission wavelength, probably due to the rigid planar structure of chromophores. It is especially noteworthy that 2,3,6,7‐tetra(4‐bromophenyl)‐1,8‐diazapyrene ( 3c ) has a larger TPA cross section than those of other molecules reported so far. These experimental results are explained in terms of the effects of extension of the π‐conjugated system, intramolecular charge transfer, and reduced detuning energy.     

Facile Synthesis and Systematic Investigations of a Series of Novel Bent‐Shaped Two‐Photon Absorption Chromophores Based on Pyrimidine

Mark us bent! The synthesis, structure, and single‐ and two‐photon spectroscopic properties of a series of pyrimidine‐based (bent‐shaped) molecules are reported. These allow structure‐property relationships and guidelines for both the development and application of TPA compounds to be derived.

     

Computational design of improved two‐photon active caging compounds based on nitrodibenzofuran

Nitrodibenzofuran (NDBF) has recently been established as photolabile protecting group and efficiently used as two‐photon active cage. In this work, a computational approach is exploited to rationally design improved two‐photon active caging groups based on this NDBF chromophore. For this objective, first the two‐photon absorption (TPA) properties of NDBF are investigated in detail and a suitable theoretical approach for the reliable simulation of TPA spectra of this class of compounds is identified. Then, virtual chemical modifications are performed by introduction of substituents at the chromophore and replacement of the central furan ring by pyrolle, thiophene, and borrole heterocycles. Subsequently, the TPA properties of the resulting compounds are computed, and the influences of the chemical modifications on TPA properties investigated in detail. The most promising candidates with largely increased two‐photon uncaging efficiencies are dimethylamino‐substituted derivatives of NDBF, nitrodibenzopyrrol, and nitrodibenzothiophene. © 2012 Wiley Periodicals, Inc.     

Poly(1,4‐diketo‐3,6‐diphenylpyrrolo[3,4‐c]pyrrole‐alt−3,6‐carbazole/2,7‐fluorene) as high‐performance two‐photon dyes

This article reports the synthesis, one‐ and two‐photon absorption, and excited fluorescence properties of poly(1,4‐diketo‐3,6‐diphenylpyrrolo[3,4‐c]pyrrole‐alt‐N‐octyl‐3,6‐carbazole/2,7‐fluorene) ( PDCZ / PDFL ). PDCZ and PDFL are synthesized by the Suzuki cross‐coupling of 2,5‐dioctyl‐1,4‐diketo‐3,6‐bis(p‐bromophenylpyrrolo[3,4‐c]pyrrole and N‐octyl‐3,6‐bis(3,3‐dimethyl‐1,3,2‐dioxaborolan‐2‐yl)carbazole or 2,7‐bis(3,3‐dimethyl‐1,3,2‐dioxaborolan‐2‐yl)fluorene and have number‐average molecular weights of 8.5 × 10³ and 1.14 × 10⁴ g/mol and polydispersities of 2.06 and 1.83, respectively. They are highly soluble in common organic solvents and emit strong orange one‐ and two‐photon excited fluorescence (2PEF) in THF solution and exhibit high light and heat stability. The maximal two‐photon absorption cross‐sections (δ) measured in THF solution by the 2PEF method using femtosecond laser pulses are 970 and 900 GM per repeating unit for PDCZ and PDFL , respectively. These 1,4‐diketo‐pyrrolo[3,4‐c]pyrrole‐containing polymers with full aromatic structure and large δ will be promising high‐performance 2PA dyes applicable in two‐photon science and technology. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 944–951     

Synthesis and two‐photon absorption properties of hyperbranched diketo‐pyrrolo‐pyrrole polymer with triphenylamine as the core

A novel hyperbranched polyyne (hb‐ DPP ) with triphenylamine as the core, 2,5‐dioctylpyrrolo [3,4‐c]pyrrole‐1,4 (2H,5H)‐dione ( DPP ) as the connecting unit has been designed and synthesized by Glaser‐Hay oxidative coupling reaction, which was characterized by IR, NMR, UV‐vis, FL, and GPC. The polymer exhibits high molecular weight (M_w up to ～6.55 × 10⁴ Da) and is readily soluble in common organic solvents such as toluene, chloroform, tetrahydrofuran, N,N‐dimethyl formamide and so on. The one‐ and two‐photon absorption (TPA) properties have been investigated. The TPA cross section of the polymer was measured by open‐aperture Z‐scan experiment using 140 femtosecond (fs) pulse, and the TPA cross section for hb‐ DPP was determined to be 579 GM per repeating unit at wavelength of 800 nm. In tetrahydrofuran, hb‐ DPP exhibits intense frequency up‐converted fluorescence with the peak located at 584 nm under the excitation of 800 nm fs pulses. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4400–4408, 2009     

The solid‐state emmissive chalcone (2E)‐1‐(5‐chlorothiophen‐2‐yl)‐3‐[4‐(dimethylamino)phenyl]prop‐2‐en‐1‐one

Orange rectangular blocks suitable for X‐ray diffraction analysis were obtained for the previously reported [Ahmad & Bano (2011). Int. J. ChemTech Res. 3 , 1470–1478] title chalcone, C₁₅H₁₄ClNOS. This solid‐emissive chalcone exhibits a planar structure and the bond parameters are compared with related compounds already described in the literature. The determination of the structure of this chalcone is quite relevant because it will play an important role in theoretical calculations to investigate potential two‐photon absorption processes and could also be useful for studying the interaction of such compounds with a biological target.     

Theoretical study on the one‐, two‐, and three‐photon absorption properties of exohedral functionalized derivative of Sc3N@C80

Geometrical structures of three investigated molecules Sc₃N@C₈₀, Sc₃N@C₈₀‐Fc, and C₆₀‐Fc were optimized by density functional theory (DFT) at the B3LYP/6‐31G* level. Then the time‐dependent DFT was employed to investigate the excited states of these molecules. After exohedral functionalization by ferrocene (Fc‐) group as the electron donor or replacing C₆₀ with Sc₃N@C₈₀ as the electron acceptor, the wavelengths of the first one‐photon absorption peak and the strongest two‐photon absorption (2PA) and three‐photon absorption (3PA) peaks shift red. The corresponding cross sections of Sc₃N@C₈₀‐Fc in the 2PA and 3PA processes increase as compared with those of Sc₃N@C₈₀, which originate from the contributions of charge transfers from Fc‐ group to C₈₀ cage and simultaneously the transfers from the C₈₀ cage to the encapsulated Sc₃N cluster. When compared with C₆₀‐Fc, the 2PA and 3PA cross sections of Sc₃N@C₈₀‐Fc decrease, which may result from the more negative charge surface of C₈₀ cage in Sc₃N@C₈₀‐Fc molecule which blocks the charge transfers from Fc‐ moiety to the C₈₀ cage in the excitation processes by compared with C₆₀‐Fc. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Synthesis,One‐ and Two‐Photon Photophysical and Excited‐State Properties,and Sensing Application of a New Phosphorescent Dinuclear Cationic Iridium(III) Complex

A new phosphorescent dinuclear cationic iridium(III) complex ( Ir1 ) with a donor–acceptor–π‐bridge–acceptor–donor (D? A? π? A? D)‐conjugated oligomer ( L1 ) as a N^N ligand and a triarylboron compound as a C^N ligand has been synthesized. The photophysical and excited‐state properties of Ir1 and L1 were investigated by UV/Vis absorption spectroscopy, photoluminescence spectroscopy, and molecular‐orbital calculations, and they were compared with those of the mononuclear iridium(III) complex [Ir(Bpq)₂(bpy)]⁺PF₆^? ( Ir0 ). Compared with Ir0 , complex Ir1 shows a more‐intense optical‐absorption capability, especially in the visible‐light region. For example, complex Ir1 shows an intense absorption band that is centered at λ=448 nm with a molar extinction coefficient (ε) of about 10⁴, which is rarely observed for iridium(III) complexes. Complex Ir1 displays highly efficient orange–red phosphorescent emission with an emission wavelength of 606 nm and a quantum efficiency of 0.13 at room temperature. We also investigated the two‐photon‐absorption properties of complexes Ir0 , Ir1 , and L1 . The free ligand ( L1 ) has a relatively small two‐photon absorption cross‐section (δ_max=195 GM), but, when complexed with iridium(III) to afford dinuclear complex Ir1 , it exhibits a higher two‐photon‐absorption cross‐section than ligand L1 in the near‐infrared region and an intense two‐photon‐excited phosphorescent emission. The maximum two‐photon‐absorption cross‐section of Ir1 is 481 GM, which is also significantly larger than that of Ir0 . In addition, because the strong B? F interaction between the dimesitylboryl groups and F^? ions interrupts the extended π‐conjugation, complex Ir1 can be used as an excellent one‐ and two‐photon‐excited “ON–OFF” phosphorescent probe for F^? ions.     

Synthesis and Photophysical Properties of Doubly β‐to‐β Bridged Cyclic ZnII Porphyrin Arrays

A series of doubly β‐to‐β bridged cyclic Zn^II porphyrin arrays were prepared by a stepwise Suzuki–Miyaura coupling reaction of borylated Zn^II porphyrin with different bridge groups. The coupling of the building block of β,β′‐diboryl Zn^II porphyrin 1 with different bridges provided the doubly β‐to‐β carbazole‐bridged Zn^II porphyrin array 3 , the fluorene‐bridged Zn^II porphyrin array 5 , the fluorenone‐bridged Zn^II porphyrin array 7 , and the three‐carbazole‐bridged Zn^II porphyrin ring 8 . The structural assignment of 3 was confirmed by the X‐ray diffraction analysis, which revealed a highly symmetrical and remarkably bent syn‐form structure. The incorporation of bridge units with different electronic effects results in different photophysical properties of the cyclic Zn^II porphyrin arrays. Comprehensive photophysical studies demonstrate that the electron‐withdrawing bridge fluorenone has the largest electronic interaction with the Zn^II porphyrin unit among the series, thus resulting in the highest two‐photon absorption cross‐section values (σ⁽²⁾) of 6570±60 GM for 7 . The present work provides a new strategy for developing porphyrin‐based optical materials.     

Synthesis,Structural Characterization,Photophysics, and Broadband Nonlinear Absorption of a Platinum(II) Complex with the 6‐(7‐Benzothiazol‐2′‐yl‐9,9‐diethyl‐9 H‐fluoren‐2‐yl)‐2,2′‐bipyridinyl Ligand

A platinum complex with the 6‐(7‐benzothiazol‐2′‐yl‐9,9‐diethyl‐9H‐fluoren‐2‐yl)‐2,2′‐bipyridinyl ligand ( 1 ) was synthesized and the crystal structure was determined. UV/Vis absorption, emission, and transient difference absorption of 1 were systematically investigated. DFT calculations were carried out on 1 to characterize the electronic ground state and aid in the understanding of the nature of low‐lying excited electronic states. Complex 1 exhibits intense structured ¹π–π* absorption at λ_abs<440 nm, and a broad, moderate ¹M LCT/¹LLCT transition at 440–520 nm in CH₂Cl₂ solution. A structured ³π–π*/³M LCT emission at about 590 nm was observed at room temperature and at 77 K. Complex 1 exhibits both singlet and triplet excited‐state absorption from 450 nm to 750 nm, which are tentatively attributed to the ¹π–π* and ³π–π* excited states of the 6‐(7‐benzothiazol‐2′‐yl‐9,9‐diethyl‐9H‐fluoren‐2‐yl)‐2,2′‐bipyridine ligand, respectively. Z‐scan experiments were conducted by using ns and ps pulses at 532 nm, and ps pulses at a variety of visible and near‐IR wavelengths. The experimental data were fitted by a five‐level model by using the excited‐state parameters obtained from the photophysical study to deduce the effective singlet and triplet excited‐state absorption cross sections in the visible spectral region and the effective two‐photon absorption cross sections in the near‐IR region. Our results demonstrate that 1 possesses large ratios of excited‐state absorption cross sections relative to that of the ground‐state in the visible spectral region; this results in a remarkable degree of reverse saturable absorption from 1 in CH₂Cl₂ solution illuminated by ns laser pulses at 532 nm. The two‐photon absorption cross sections in the near‐IR region for 1 are among the largest values reported for platinum complexes. Therefore, 1 is an excellent, broadband, nonlinear absorbing material that exhibits strong reverse saturable absorption in the visible spectral region and large two‐photon‐assisted excited‐state absorption in the near‐IR region.     

Toward assessment of density functionals for vibronic coupling in two‐photon absorption: A case study of 4‐nitroaniline

In this study, we predict vibronic two‐photon absorption (TPA) spectra for 4‐nitroaniline in vacuo. The simulations are performed using density functional theory and the approximate second‐order coupled‐cluster singles and doubles model CC2. Thereby we also demonstrate the possibility of simulations of vibronic TPA spectra with ab initio wavefunction methods that include electron correlation for medium‐sized systems. A special focus is put on the geometric derivatives of the second‐order transition moment and the dipole moment difference between the charge‐transfer excited state and the ground state. The results of CC2 calculations bring new insight into the vibronic coupling mechanism in TPA spectra of 4‐nitroniline and demonstrate that the mixed term is quite large and that it also exhibits a negative interference with the Franck‐Condon contribution. © 2015 Wiley Periodicals, Inc.