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     

Alternating copolymers of 2,6‐bis(p‐dihexylaminostyryl)anthracene‐9,10‐diyl and N‐octylcarbazole with large two‐photon cross sections

We report the synthesis, thermal, one‐ and two‐photon properties of poly(2,6‐bis(p‐dihexylaminostyryl)anthracene‐9,10‐diyl‐alt‐N‐octylcarbazole‐3,6‐/2,7‐diyl) ( P1/P2 ). The as‐synthesized polymers exhibit number‐average molecular weights of 1.7 × 10⁴ for P1 and 2.1 × 10⁴ g/mol for P2 . They emit strong one‐ and two‐photon excitation fluorescence with the peak around 502 nm, and the fluorescence quantum yields around 0.76 in chloroform. In film state, P1 and P2 show different red‐shift emission with the peaks at 512 nm and 523 nm, respectively. The DSC measurement reveals that as‐synthesized polymers are all amorphous aggregates with the glass transition temperatures of 131 °C for P1 and 152 °C for P2 . The solution two‐photon absorption (TPA) properties of P1 and P2 in chloroform are measured by the two‐photon‐induced fluorescence method using femtosecond laser pulses (120 fs). The TPA cross sections (δ) are measured over the range of 700–900 nm. The maximal δ of P1 and P2 all appear at ～800 nm and are 1010 GM and 940 GM per repeating unit, respectively. This suggests that no notable interactions among structure units that impair their fluorescence and TPA properties, and the polymers with large δ can be obtained by using the high TPA‐active units as building blocks. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Synthesis,characterization, and large two‐photon absorption cross‐sections of solid red‐emitting 1,4‐diketo‐3,6‐diphenylpyrrolo [3,4‐c]pyrrole/3,6‐carbazole/terfluorene copolymers

The synthesis, one‐ and two‐photon absorption (TPA) and emission properties of three novel 1,4‐diketo‐3,6‐diphenylpyrrolo[3,4‐c]pyrrole (DPP)/3,6‐carbazole (Cz)/terfluorene (TF) copolymers are reported. The molar ratios of DPP versus TF are 15:85 ( TCP15 ), 25:75 ( TCP25 ), and 50:50 ( TCP50 ) under Cz:(TF + DPP) = 1. Two distinguished one‐photon absorption and emission bands observed in solutions imply that the electronic states of Cz–DPP–Cz and Cz–TF–Cz are not well mixed and the energy transfer from TF segments to DPP units is incomplete. However, in film states, all three copolymers are monochromatic red emitting with the peak wavelengths at 617, 621, and 631 nm for TCP15 , TCP25 , and TCP50 , respectively, indicating that the interchain interactions also have played an important role in the energy transfer. In two‐photon measurement, the copolymer solutions still exhibit two distinguished emission bands but the relative intensities at short‐wavelength region are obviously decreased, implying that Cz–TF–Cz segment is high one‐photon active but low TPA active, whereas Cz–DPP–Cz unit is low one‐photon active but high TPA active. All the copolymers show large δ over the range of measured wavelengths and the δ values of TCP15 , TCP25 , and TCP50 increase with DPP contents and are up to 530, 770, and 850 GM per repeating unit, respectively. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Two‐Photon Absorption Properties of Dehydrobenzo[12]annulenes and Hexakis(phenylethynyl)benzenes: Effect of Edge‐Linkage

Two‐photon absorption (TPA) properties of two trefoil‐shaped compounds with different edge linkages—tris(hexadehydrotribenzo[12]annulene) and tris(tetradehydrotribenzo[12]annulene)—and three asterisk‐shaped compounds having no edge‐linkage—hexakis(phenylethynyl)benzenes—are investigated experimentally by the open‐aperture Z‐scan and TPA‐induced fluorescence methods with wavelength tuneable femtosecond pulses. The compound with ethynylene edge‐linkage exhibits the most intense TPA (the maximal TPA cross section is 1300±170 GM at 572 nm where 1 GM=10^?50 cm⁴ s molecule^?1 photon^?1). The TPA activity of the compounds is primarily explained in terms of the planarity of the molecules in relation with the type of edge‐linkage.     

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,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.     

A Diradical Approach towards BODIPY‐Based Dyes with Intense Near‐Infrared Absorption around λ=1100 nm

A diradical approach to obtain stable organic dyes with intense absorption around λ=1100 nm is reported. The para‐ and meta‐quinodimethane‐bridged BODIPY dimers BD‐1 and BD‐2 were synthesized and were found to have a small amount of diradical character. These molecules exhibited very intense absorption at λ=1088 nm (?=6.65×10⁵ M ^?1 cm^?1) and 1136 nm (?=6.44×10⁵ M ^?1 cm^?1), respectively, together with large two‐photon‐absorption cross‐sections. Structural isomerization induced little variation in their diradical character but distinctive differences in their physical properties. Moreover, the compounds showed a selective fluorescence turn‐on response in the presence of the hydroxyl radical but not with other reactive oxygen species.     

A Theranostic Agent Combining a Two‐Photon‐Absorbing Photosensitizer for Photodynamic Therapy and a Gadolinium(III) Complex for MRI Detection

The convergent synthesis and characterization of a potential theranostic agent, [DPP‐ZnP‐GdDOTA]^?, which combines a diketopyrrolopyrrole‐porphyrin component DPP‐ZnP as a two‐photon photosensitizer for photodynamic therapy (PDT) with a gadolinium(III) DOTA complex as a magnetic resonance imaging probe, is presented. [DPP‐ZnP‐GdDOTA]^? has a remarkably high longitudinal water proton relaxivity (19.94 mm ^?1 s^?1 at 20 MHz and 25 °C) for a monohydrated molecular system of this size. The Nuclear Magnetic Relaxation Dispersion (NMRD) profile is characteristic of slow rotation, related to the extended and rigid aromatic units integrated in the molecule and to self‐aggregation occurring in aqueous solution. The two‐photon properties were examined and large two‐photon absorption cross‐sections around 1000 GM were determined between 910 and 940 nm in DCM with 1 % pyridine and in DMSO. Furthermore, the new conjugate was able to generate singlet oxygen, with quantum yield of 0.42 and 0.68 in DCM with 1 % pyridine and DMSO, respectively. Cellular studies were also performed. The [DPP‐ZnP‐GdDOTA]^? conjugate demonstrated low dark toxicity and was able to induce high one‐photon and moderate two‐photon phototoxicity on cancer cells.     

Polar Diketopyrrolopyrrole‐Imidazolium Salts as Selective Probes for Staining Mitochondria in Two‐Photon Fluorescence Microscopy

Three rationally designed polar derivatives of diketopyrrolopyrrole consisting of 1,3‐dimethylimidazolium cationic units and benzene, thiophene, or furan rings as π spacers were synthesized and thoroughly studied. The obtained salts are soluble in polar organic solvents and show satisfactory solubility in water, which makes them suitable for the applications in bioimaging. Photophysical measurements revealed that the obtained derivatives are characterized by strong absorption and good fluorescence quantum yields. The corresponding two‐photon properties were also examined and showed that the synthesized salts exhibit large two‐photon absorption cross‐sections reaching 4000 GM (GM=Goeppert‐Mayer unit, 1 GM=10^?50 cm⁴ s photon^?1) and very high two‐photon brightness values exceeding 2000 GM. It was demonstrated that these salts can be safely applied in two‐photon fluorescence microscopy for selective staining of mitochondria in living cells.     

Characterization of two‐ and three‐photon absorption of polyfluorene derivatives

Fluorene‐based polymer derivatives are promising materials for organic electronic devices because of their photoluminescence and electroluminescence, good film‐forming ability, and favorable chemical and thermal properties. Although optical properties of polyfluorene have already been reported, most of the studies focused on the linear optical properties, whereas nonlinear optical characteristics have only recently received more detailed attention. Here, we report on two polyfluorene derivatives, poly(9,9′‐n‐dihexyl‐2,7‐fluorenediyl) (LaPPS 10) and poly(9,9′‐n‐dihexyl‐2,7‐fluorene‐diyl‐vinylene) (LaPPS 38), which present intense nonlinear absorption and fluorescence. Two‐photon absorption cross‐section properties of both polymers were characterized in the spectral range from 500 nm up to 900 nm, reaching peak values around 2000 Göppert Mayer units. Optical limiting behavior and two‐photon‐induced fluorescence of both polymers have also been investigated. Furthermore, the first molecular hyperpolarizability of the polymers was also studied using hyper‐Rayleigh scattering. In addition, the three‐photon absorption (3PA) spectra of both materials were also investigated, and 3PA cross‐section values in the order of 1 × 10^?78 cm⁶ s² photon^?2 were observed. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 747–754     

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     

Superfluorescent Squaraine with Efficient Two‐Photon Absorption and High Photostability

The synthesis, linear photophysical, two‐photon absorption (2PA), femtosecond transient absorption, and superfluorescence properties of a new symmetrical squaraine derivative ( 1 ) are reported. Steady‐state linear spectral and photochemical properties, fluorescence lifetimes, and excitation anisotropy of 1 were investigated in various organic solvents. High fluorescence quantum yields (≈0.7) and very high photostability (photodecomposition quantum yields ≈10^?6–10^?8) were observed. An open‐aperture Z‐scan method was used to obtain 2PA spectra of 1 over a broad spectral range (maximum 2PA cross section ≈1000 GM). Excited‐state absorption (ESA) and gain was observed by femtosecond transient absorption spectroscopy, in which both reached a maximum at approximately 500 fs. Squaraine 1 exhibits efficient superfluorescence. The quantum chemical study of 1 revealed the simulated vibronic nature of the 1PA and 2PA spectra were in good agreement with experimental data; this may provide the ability to predict potential advanced photonic materials.     

Study of Linear and Nonlinear Optical Properties of Four Derivatives of Substituted Aryl Hydrazones of 1,8‐Naphthalimide

Four 1,8‐naphthalimide hydrazone molecules with different electron‐donating groups have been applied in the study of linear and nonlinear optical (NLO) properties. These compounds showed strong green emission in solution. Their NLO properties such as two‐photon absorption (TPA) behavior with femtosecond laser pulses ca. 800 nm and excited‐state absorption (ESA) behavior with nanosecond laser pulses at 532 nm were investigated. Compound 4 presented the largest two‐photon cross section (550 GM) among them due to two factors: the conjugated length of compound 4 is the longest and the electron‐donating ability of compound 4 is the strongest. Different from TPA behavior, compound 2 showed the best nonlinear absorption properties at 532 nm and its nonlinear absorption coefficient and third‐order nonlinear optical susceptibilities χ ⁽³⁾ were up to 1.41×10^?10 MKS and 4.65×10^?12 esu, respectively. Through the modification of the structure, the nonlinear optical properties of these compounds at different wavelengths (532 and 800 nm) were well tuned. The great broad‐band nonlinear optical properties indicate hydrazones are good candidates for organic nonlinear optical absorption materials.     

乙酸/三氟化硼乙醚混合电解质中咔唑的电化学聚合

在新型混合电解质——乙酸含体积比26%的三氟化硼乙醚和5%的分子量为400的聚乙二醇中直接氧化咔唑制得高质量的聚咔唑膜,导电率为10-2 S·cm-1。在该体系中,咔唑的起始氧化电位相对于饱和甘汞电极只有0.89 V,远低于在含0.1 mol·L-1四氟化硼四丁基铵的乙腈溶液中的1.36V（相对于饱和甘汞电极）。从该体系中获得的聚咔唑膜具有良好的电化学性质和热稳定性,可以部分溶于二甲基亚砜、四氢呋喃等强极性溶剂。荧光光谱表明该体系中获得的聚咔唑膜是一种良好的蓝光发射材料。红外、核磁波谱和理论量子化学计算结果表明,咔唑的电化学聚合主要发生在3,6位。据我们所知,这是利用乙酸三氟化硼乙醚混合电解质进行电化学聚合的首次报道。     

Simple Bipolar Hosts with High Glass Transition Temperatures Based on 1,8‐Disubstituted Carbazole for Efficient Blue and Green Electrophosphorescent Devices with “Ideal” Turn‐on Voltage

Two hybrids based on 1,8‐disubstituted carbazole, 1,8‐OXDCz and 1,8‐mBICz , have been designed and synthesized through a facile process. The incorporation of oxadiazole or N‐phenylbenzimidazole moieties at the 1,8‐positions of carbazole greatly improves its morphological stability, giving glass transition temperatures (T_g) as high as 138 and 154 °C, respectively. Blue phosphorescent organic light‐emitting devices (PhOLEDs) with 1,8‐mBICz exhibit almost the same performance as a similarly structured device based on the mCP host, and green PhOLEDs employing the new host material 1,8‐OXDCz exhibit an ideal turn‐on voltage (2.5 V at 1.58 cd m^?2), a maximum current efficiency (η_c,max) of 73.9 cd A^?1, and a power efficiency (η_p,max) of 89.7 lm W^?1. These results are among the best performances of [Ir(ppy)₃]‐based devices with simple device configurations.     

New Organic Dye Based on a 3,6‐Disubstituted Carbazole Donor for Efficient Dye‐Sensitized Solar Cells

We have synthesized and characterized four organic dyes ( 9 , 10 , H1 , H2 ) based on a 3,6‐disubstituted carbazole donor as sensitizers in dye‐sensitized solar cells. These dyes have high molar extinction coefficients and energy levels suitable for electron transfer from an electrolyte to nanocrystalline TiO₂ particles. Under standard air mass 1.5 global (AM 1.5 G) solar irradiation, a device using dye H4 exhibits a short‐circuit current density (J_sc) of 13.7 mA cm^?2, an open‐circuit voltage (V_oc) of 0.68 V, a fill factor (FF) of 0.70, and a calculated efficiency of 6.52 %. This performance is comparable to that of a reference cell based on N719 (7.30 %) under the same conditions. After 1000 hours of visible‐light soaking at 60 °C, the overall efficiency remained at 95 % of the initial value.     

Ethynylene‐Linked Oligomers Based on Benzodithiophene: Synthesis and Photoelectric Properties

Two conjugated ethynyl‐linked oligomers, oligo(benzodithiophene‐ethynylene‐benzothiadiazole) (O1) and oligo(benzodithiophene‐ethynylene‐carbazole) (O2), were synthesized by Sonogashira coupling reaction. Their degrees of polymerization were 7 and 10, respectively. Their photophysical and electrochemical properties were investigated. O1 exhibitd two strong absorption bands at 404 nm and 483 nm, and O2 at 401 nm and 429 nm. The results of UV‐Vis, cyclic voltammetry (CV) and theoretical calculations showed that O1 has a narrower band gap than O2. The conductivities of O1 and O2 were 1.05×10^?15 and 6.98×10^?16 S/cm, respectively, and would increase to 1.23×10^?10 and 1.05×10^?10 S/cm after doping with iodine.     

Synthesis and Nonlinear Optical Properties of a New A-π-A Two-Photon Compound Utilizing Dibenzothiophene as Center

A new two‐photon material, 3E,6E‐bis(2‐pyrid‐4′‐ylvinyl)dibenzothiophene (BPVDBT), has been firstly synthesized by an efficient Pd‐catalyzed Heck coupling route. The single‐ and two‐photon fluorescence, quantum yields, lifetimes, solvent effects of the chromophore were studied in detail and the compound exhibited solvent‐sensitivity. The fluorescence intensity (I_out) and input excitation intensity (I_in) can fit in well with the quadratic parabolas, which indicates that the up‐converted fluorescence was induced by the two‐photon absorption (TPA). TPA cross‐section of BPVDBT has been measured using the two‐photon‐induced fluorescence method, whose value is 14.24×10^?50 cm⁴·s·photon^?1·molecule^?1 at 750 nm. The experimental results confirm that BPVDBT is a good two‐photon absorbing chromophore with an A‐π‐A type.     

Synthesis,Photophysical Properties and Two‐Photon Absorption Study of Tetraazachrysene‐based N‐Heteroacenes

Three novel N‐heteroacene molecules ( SDNU‐1 , SDNU‐2 and SDNU‐3 ) based on tetraazachrysene units as cores have been designed, synthesized and fully characterized. Their photophysical, electrochemical and fluorescence properties were investigated, and they exhibited blue to green emission in the solid state. Interestingly, SDNU‐2 exhibited high solid photoluminescence quantum efficiencies (75.3 %), which is the highest value of N‐heteroacenes derivatives to date. Two‐photon absorption studies have been conducted by using the open and close aperture Z‐san technique. SDNU‐3 showed a significant enhancement in the two‐photon absorption cross‐section with magnitudes as high as about 700 GM (1 GM=1×10^?50 cm⁴ s/photon) when excited with 800 nm light, which is the largest value based on a heteroacene system measured by using a Z‐scan experiment so far. We attribute the outcome to sufficient electronic coupling between the strong charge transfer of quadrupolar substituents and the tetraazachrysene core. Our result would provide a new guideline to design novel efficient two‐photon materials based on N‐heteroacene cores.     

Zethrene and Dibenzozethrene: Masked Biradical Molecules?

The syntheses, structures, and physical properties of dibenzozethrenes were explored. The results thus obtained were compared with those for zethrenes. Dibenzozethrenes were synthesized by the nickel‐catalyzed cyclodimerization of 9‐ethynyl‐1‐iodoanthracenes. The substituents in zethrene and dibenzozethrene twisted their backbones, and remarkably influenced their properties. Unlike closed‐shell disubstituted derivatives, the parent zethrene and dibenzozethrene are singlet open‐shell biradicals, which were studied by variable‐temperature ¹H NMR, ESR, SQUID and computational methods. Since substituents were observed to affect significantly the biradical properties, the relevant mechanisms were analyzed. The nonlinear optical performance of each of these compounds depends on its π‐conjugation and biradical properties. Dibenzozethrenes have larger two‐photon absorption cross‐sections than zethrenes, as most strongly evidenced by the parent dibenzothrene [σ_max=4323 GM at 530 nm].