取代基对二噻吩并噻吩衍生物的双光子吸收性质的影响

利用ZINDO/SOS方法, 从理论上研究了对称和不对称取代两种情况下, 取代基对二噻吩并噻吩衍生物单双光子吸收性质的影响. 结果表明, 所设计的噻吩类分子具有较大的双光子吸收截面, 且双受体取代比双给体取代更有利于增大分子的双光子吸收截面. 同时发现, 此类分子受体取代可以显著增加波长较短的双光子峰附近的双光子吸收, 而给体取代则可以改善波长较长吸收峰附近的双光子吸收.     

双光子吸收材料的分子设计研究

介绍了双光子吸收材料分子设计原理.为了设计有大的双光子吸收响应的材料,对多种分子进行了系统的理论研究.用量子化学密度泛函理论和AM1方法进行分子几何构型优化.在优化结构的基础上,用ZINDO和自编程序求得分子的单、双光子吸收性质.设计了一些未知化合物,以期为合成新的具有大的双光子吸收截面的材料提供理论根据.以双层二聚二甲苯邻甲酸衍生物、铂乙炔化物、卟啉衍生物、C60、C70、八极矩分子为例,报道了我们在这方面的研究结果.     

3,6-和2,7-咔唑衍生物单光子和双光子吸收性质的理论研究

采用密度泛函理论B3LYP方法以及ZINDO/SDCI方法计算3,6-和2,7-咔唑衍生物的分子平衡几何结构、电子结构及单光子和双光子吸收性质.乙烯基吡啶取代基的位置影响分子的单光子和双光子吸收性质.与3,6-咔唑衍生物相比,2,7-咔唑衍生物的单光子吸收波长红移,振子强度增大;双光子吸收波长红移,双光子吸收截面增加.结果表明,2,7-咔唑衍生物是更好的双光子吸收材料.     

1,4-二(4'-N,N-二苯胺基苯乙烯基)苯衍生物单双光子吸收性质的理论研究

随着双光子显微技术的发展,获得性质优良的双光子荧光染料成为研究热点.因此,通过密度泛函理论(DFT)对一系列D-π-A-π-D型1,4-二(4'-N,N-二苯胺基苯乙烯基)苯(DPA-DSB)衍生物平衡几何结构、电子结构、单双光子吸收以及荧光发射性质进行了理论研究,对其结构和光学性质的分析表明,对A,π结构元进行修饰或更换可有效地调节光谱;向分子片段A引入杂原子可有效提高双光子吸收截面;和乙烯基团相比,π桥为乙炔基,若对分子平面性改变不大,则导致分子双光子吸收截面值减小,若乙炔桥很大程度改善分子平面性,则导致分子的TPA截面增大.本研究旨在理解DPA-DSB衍生物分子结构与双光子性质间的关系,为设计合成新型双光子材料提供重要信息.     

扩展卟啉分子的多光子吸收特性

发展关联电子体系的多参考组态相互作用方法, 应用态求和的张量方法, 计算研究了三种扩展卟啉分子的多光子吸收特性. 计算结果表明, 通过中间插入噻吩杂环基团, 扩展卟啉分子的双光子和三光子吸收峰发生较大红移, 对应的吸收截面得到显著的提高, 并且三光子吸收截面的增加更为明显; 但是由于卟啉环扩大导致分子平面发生扭曲, 三光子吸收截面的增大趋势明显减弱.     

两个系列星型准八极矩分子单光子和双光子吸收性质的理论研究

采用DFT/B3LYP/6-31G*和ZINDO-SOS方法, 系统地研究了两个系列(以苯为中心的a系列和以三苯胺为中心的b系列)星型准八极矩分子及其单枝物的单光子和双光子吸收性质. 结果表明, b系列分子有较大的双光子吸收截面和更长的单光子和双光子吸收波长. 星型三分枝分子的双光子吸收截面较其单个分枝增长了超过3倍因为存在分枝间的相互作用. 含1,3,4-噁二唑的分子比含2,1,3-苯并噻二唑的分子有更大的双光子吸收截面但是最大吸收波长却蓝移, 不在红外或近红外区域.     

分枝结构对以N为耦合中心的多分枝分子的双光子吸收性质的影响

采用ZINDO/SOS方法,研究了以N原子为耦合中心,以二苯乙烯类、噻吩类和芴类分子作为分枝的分子的双光子吸收性质,从而研究了分枝结构对多分枝分子的双光子吸收性质的影响.结果表明分枝结构会影响分枝之间耦合作用的强弱,因而对分子的双光子吸收性质具有重要影响.所设计的分子中以二苯乙烯类和噻吩类分子作为分枝的多分枝分子具有较大的双光子吸收截面.     

两类以芴为中心的有机分子双光子吸收特性

在密度泛函理论水平上, 利用响应函数方法研究了实验新合成的两类以芴为π中心的分子(SK-G1和NT-G1)的双光子吸收特性. 计算结果表明, 这两类有机分子都具有较大的单光子和双光子光吸收强度. 在低能量范围内, NT-G1分子的最大单光子吸收峰相对于SK-G1分子来说发生了红移, 且其最大单光子吸收强度是SK-G1分子的两倍. SK-G1和NT-G1分子的最大双光子吸收均发生在第二激发态. NT-G1分子的最大双光子吸收截面约是SK-G1分子的五倍, 并且NT-G1分子存在一个较宽的双光子吸收带. NT-G1分子的较强光学性质与分子内较大的电荷转移过程有关. 采用Onsager模型计算了溶剂分子对溶质分子单光子吸收性质的影响, 理论计算结果和实验测量结果符合得较好.     

DCM衍生物双光子吸收截面的溶剂效应

考察了以三苯胺基为给电子基团的4种不同DCM衍生物在有机溶剂中的单光子光物理性质(基态和激发态永久偶极矩差、光学跃迁偶极矩以及跃迁能量等), 并利用双光子诱导荧光法考察了溶剂对其双光子吸收截面(δtpa)的影响. 研究结果表明, DCM衍生物的光学跃迁具有显著的分子内电荷转移特性, 不同末端取代基主要影响其稳态光谱性质, 而分支结构数目主要影响其双光子吸收截面. 研究结果还发现, 双光子吸收截面随分子结构的变化趋势符合双能级模型, 拉电子基团为丙二腈和1,3-茚二酮的DCM衍生物的δtpa随溶剂介电常数的增加呈现不同的变化趋势.     

具有大的双光子吸收截面的四羧酸二萘嵌苯衍生物的理论研究

用密度泛涵方法和ZINDO方法,从理论上研究了一系列四羧酸二萘嵌苯的衍生物(PTCDS)。对其平衡几何、电子结构和单双光子吸收性质进行了详细的计算研究。结果表明,此系列衍生物的双光子吸收截面主要由其主体结构(二萘嵌苯)决定。△EH-Lgap (HOMO与LUMO间的能隙)的减小,HOMO轨道能量的增大,分子主轴两端取代基给电子强度的增强,共轭长度的增大,分子刚性的增强都有利于此系列化合物双光子吸收截面的增大。并设计了比文献[22]报道的分子C有更大的双光子吸收截面的两个分子D1,D2。     

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.     

A p‐Quinodimethane‐Bridged Porphyrin Dimer

A p‐quinodimethane (p‐QDM)‐bridged porphyrin dimer 1 has been prepared for the first time. An unexpected Michael addition reaction took place when we attempted to synthesize compound 1 by reaction of the cross‐conjugated keto‐linked porphyrin dimers 8 a and 8 b with alkynyl/aryl Grignard reagents. Alternatively, compound 1 could be successfully prepared by intramolecular Friedel–Crafts alkylation of the diol‐linked porphyrin dimer 14 with concomitant oxidation in air. Compound 1 shows intense one‐photon absorption (OPA, λ_max=955 nm, ε=45400 M ^?1 cm^?1) and a large two‐photon absorption (TPA) cross‐section (σ⁽²⁾_max=2080 GM at 1800 nm) in the near‐infrared (NIR) region due to its extended π‐conjugation and quinoidal character. It also exhibits a short singlet excited‐state lifetime of 25 ps. The cyclic voltammogram of 1 displays multiple redox waves with a small electrochemical energy gap of 0.86 eV. The ground‐state geometry, electronic structure, and optical properties of 1 have been further studied by density functional theory (DFT) calculations and compared with those of the keto‐linked dimer 8 b . This research has revealed that incorporation of a p‐QDM unit into the porphyrin framework had a significant impact on its optical and electronic properties, leading to a novel NIR OPA and TPA chromophore.     

π‐Conjugation Enlargement Toward the Creation of Multi‐Porphyrinic Systems with Large Two‐Photon Absorption Properties

Recent progress in the synthesis of covalently linked porphyrin arrays with large two‐Photon absorption (TPA) cross‐section values has been reviewed with a particular focus on the relation of TPA properties with molecular structures. Covalently linked porphyrin arrays continue to be important and useful for the creation of functional materials owing to their chemical robustness, fine‐tuning, and easy manipulation. More importantly, the porphyrin electronic systems are quite susceptible to periphery conjugative perturbations, hence allowing facile fabrications to extensively delocalized systems. This property has been used for exploration of porphyrin‐based molecular systems with large TPA values, demonstrating a general trend that enhancement in electronic interactions leads to large TPA cross‐section values. As a representative example, the porphyrin tapes exhibit larger TPA values owing to the fully delocalized nature of the π‐electrons. This Focus Review will help understand the structural requirements of porphyrin arrays with large TPA values, which will be useful for future applications in optical communication in the IR region.     

Synthesis,Two‐Photon Absorption and Optical Limiting Properties of Multi‐branched Styryl Derivatives Based on 1,3,5‐Triazine

Five new multi‐branched two‐photon absorption triazine chromophores ( T1 – T5 ) with different donor strength, conjugation length, and direction of charge transfer have been designed and synthesized. The one‐photon fluorescence, fluorescence quantum yields, and two‐photon properties have been investigated. The two‐photon absorption (2PA) cross sections measured by the open aperture Z‐scan technique were determined to be 447, 854, 1023, 603, and 766 GM for T1 , T2 , T3 , T4 , and T5 , respectively. This result indicates that their 2PA cross section values (σ) increase with increasing electron‐donating strength of the end group, extending the conjugation length of the system, and introducing electron‐withdrawing perfluoroalkyl as side groups to the end donor. In addition, the σ value of T5 is also larger than that of T1 , which provides evidence that the σ value is relative to the direction of charge transfer (from the ends to the center of the molecule or from the center to the ends). Moreover, significant enhancement of the two‐photon absorption cross section was achieved by introducing a thiophene moiety to a conjugated CC bond. At the same time, the optical limiting behavior for these chromophores was studied by using a focused 800 nm laser beam with pulses of 140 fs duration. It was found that these molecules also exhibit good optical limiting properties. These initial results clearly demonstrate that multi‐branched triazine chromophores are a highly suitable class of two‐photon absorbing materials.     

An insight into a novel class of self-assembled porphyrins: geometric structure, electronic structure, one- and two-photon absorption properties

We have theoretically investigated a series of butadiyne-linked porphyrin derivatives that exhibit large two-photon absorption (TPA) cross sections in the visible-IR range. The electronic structure, one-photon absorption (OPA), and TPA properties have been studied in detail. We found that the introduction of a butadiyne linkage and the increase of the molecular dimensionality from monomer to dimer determine the OPA intensities of Q band and Soret band, respectively. A most important role for the enhancement of the TPA cross section is played by introducing a butadiyne bridge. The complementary coordination and the combination of the terminal free base and the core zinc porphyrin are also two effective factors for the enhancement of the TPA efficiency. The dimer with two porphyrins linked at meso-positions by a butadiyne linkage results in a maximum TPA cross section (79.35 x 10(-48) cm4 s per photon). Our theoretical findings are consistent with the recent experimental observations. This series of porphyrin derivatives as promising TPA materials are the subject of further investigation.     

Synthesis and Characterization of Two‐Photon Active Chromophores Based on Tetrathienoacene (TTA) and Dithienothiophene (DTT)

Three new donor–π–donor (D‐π‐D) tetrathienoacene (thieno[2′,3′:4,5]thieno[3,2‐b]thieno[2,3‐d]thiophene (TTA))‐cored chromophores, end‐functionalized with electron‐donating triphenylamine (TPA) groups, were developed and characterized for their two‐photon‐related properties by using both nano‐ and femtosecond laser pulses as the probing tools. TTA‐based chromophores exhibit stronger and more widely dispersed two‐photon absorption (2PA) than those of dithienothiophene (DTT)‐based congeners. As a consequence, the bithiophene‐conjugated TTA chromophore exhibits the highest maximum 2PA cross‐section value (up to 2500 GM) with good thermal stability, and thus, it is the best performing two‐photon chromophore among the studied model compounds. The bithiophene‐conjugated DTT analogue exhibits the second highest maximum two‐photon absorptivity of 1950 GM, which is nearly 7 times larger than that of previously reported DTT‐based chromophores.     

Theoretical investigation of one-photon and two-photon absorption properties for multiply N-confused porphyrins

We have theoretically investigated a series of multiply N-confused porphyrins and their Zn or Cu complexes for the first time by using DFT(B3LYP/6-31G*) and ZINDO/SOS methods. The electronic structure, one-photon absorption (OPA), and two-photon absorption (TPA) properties have been studied in detail. The calculated results indicate that the OPA spectra of multiply N-confused porphyrins are red-shifted and the OPA intensities decrease compared to normal porphyrin. The maximum two photon absorption wavelengths lambda(max) are blue-shifted and the TPA cross sections delta(max) are increased 22.7-112.1 GM when the N atoms one by one are inverted from core to beta position to form multiply N-confused porphyrins. Especially delta(max) of N3CP get to 164.7 GM. The electron donors -C6F5s at meso-position can make the TPA cross section delta(max) increase. After forming metal complexes with Cu or Zn, the TPA properties of multiply N-confused porphyrins are further increased except for N3CP, N4CP. Our theoretical findings demonstrate that the multiply N-confused prophyrins as well as their metal complexes and derivatives are promising molecules that can be assembled series of materials with large TPA cross section, and are sure to be the subject of further investigation.     

Experimental and Theoretical Studies of Quadrupolar Oligothiophene‐Cored Chromophores Containing Dimesitylboryl Moieties as π‐Accepting End‐Groups: Syntheses,Structures, Fluorescence,and One‐ and Two‐Photon Absorption

Quadrupolar oligothiophene chromophores composed of four to five thiophene rings with two terminal (E)‐dimesitylborylvinyl groups ( 4 V – 5 V ), and five thiophene rings with two terminal aryldimesitylboryl groups ( 5 B ), as well as an analogue of 5 V with a central EDOT ring ( 5 VE ), have been synthesized via Pd‐catalyzed cross‐coupling reactions in high yields (66–89 %). Crystal structures of 4 V , 5 B , bithiophene 2 V , and five thiophene‐derived intermediates are reported. Chromophores 4 V , 5 V , 5 B and 5 VE have photoluminescence quantum yields of 0.26–0.29, which are higher than those of the shorter analogues 1 V – 3 V (0.01–0.20), and short fluorescence lifetimes (0.50–1.05 ns). Two‐photon absorption (TPA) spectra have been measured for 2 V – 5 V , 5 B and 5 VE in the range 750–920 nm. The measured TPA cross‐sections for the series 2 V – 5 V increase steadily with length up to a maximum of 1930 GM. We compare the TPA properties of 2 V – 5 V with the related compounds 5 B and 5 VE , giving insight into the structure–property relationship for this class of chromophore. DFT and TD‐DFT results, including calculated TPA spectra, complement the experimental findings and contribute to their interpretation. A comparison to other related thiophene and dimesitylboryl compounds indicates that our design strategy is promising for the synthesis of efficient dyes for two‐photon‐excited fluorescence applications.     

Degenerate Two‐Photon Absorption and Effective Optical‐Power‐Limiting Properties of Multipolar Chromophores Derived from 2,3,8‐Trisubstituted Indenoquinoxaline

Two analogous multipolar chromophores ( 1 and 2 ) that contained 2,3,8‐trisubstituted indenoquinoxaline moieties have been synthesized and characterized for their two‐photon absorption properties, both in the femtosecond and nanosecond time regimes. We demonstrated that their multi‐branched framework structures, which incorporated appropriately functionalized indenoquinoxaline units, afforded large molecular nonlinear absorptivities within the studied spectroscopic range. Effective optical‐power‐limiting and stabilization behaviors in the nanosecond regime of dye molecule ( 2 ) were also investigated and the results indicated that such a structural motif could be a useful approach to the molecular design of highly active two‐photon systems for quick‐response and related broadband optical‐suppressing applications, in particular for confronting laser pulses of a long duration.     

Water‐Soluble Triarylborane Chromophores for One‐ and Two‐Photon Excited Fluorescence Imaging of Mitochondria in Cells

Three water‐soluble tetracationic quadrupolar chromophores comprising two three‐coordinate boron π‐acceptor groups bridged by thiophene‐containing moieties were synthesised for biological imaging applications. Compound 3 containing the bulkier 5‐(3,5‐Me₂C₆H₂)‐2,2′‐(C₄H₂S)₂‐5′‐(3,5‐Me₂C₆H₂) bridge is stable over a long period of time, exhibits a high fluorescence quantum yield and strong one‐ and two‐photon absorption (TPA), and has a TPA cross section of 268 GM at 800 nm in water. Confocal laser scanning fluorescence microscopy studies in live cells indicated localisation of the chromophore at the mitochondria; moreover, cytotoxicity measurements proved biocompatibility. Thus, chromophore 3 has excellent potential for one‐ and two‐photon‐excited fluorescence imaging of mitochondrial function in cells.