Influence of acceptor tethering on the performance of nonlinear optical properties for pyrene-based materials with A-π-D-π-D architecture

In this study, we designed a series of pyrene-based donor-π-donor-π-acceptor compounds (HPTC1-HPTC7) by structural tailoring the reference compound (HPTC) using acceptor units. Nonlinear optical (NLO) properties, frontier molecular orbitals (FMOs), natural bonding orbital (NBO), transition density matric (TDM) analysis, and absorption spectra of reference and proposed derivatives were calculated at M06/6-31G(d,p) functional. All the designed compounds have smaller energy bandgaps than the HPTC compound. Moreover, the designed compounds exhibited larger global softness values than the reference. The absorption maxima of HPTC2, HPTC3, and HPTC7 are blue shifted with respect to HPTC. NBO analysis revealed that prolonged hyper conjugative associations and strong interactions between the donor (π) and acceptor (π*) moieties play a crucial part in their stabilization. The FMO and NBO findings supported the NLO responses of entitled compounds, and consequently, the linear and nonlinear properties of designed derivatives elevate compared to the reference molecule. Promisingly, the NLO response for HPTC7 comprises of highest values of <α>, β_total and < γ > as 1.92 × 10^?22 esu, 1.95 × 10^?27 esu, and 4.69 × 10⁷ (a.u). This NLO behavior shows push–pull NLO chromophores for HPTC7 predicting its role in pursuing NLO materials for optoelectronic applications.     

Carbazole-Based Mono and Bis-styryl NLOphores: Structure Property Correlations

A detailed study of linear and nonlinear optical (NLO) properties obtained by spectroscopy and DFT computations of carbazole-based D-π-A (mono) and A-π-D-π-A (bis) extended styryl dyes is presented. Four different DFT functionals, B3LYP, MO6, BHandHLYP, and CAM-B3LYP are used for computations. The structure–property relationship is examined by correlating bond length alternation/bond order alternation with NLO properties of the dyes. The bis-carbazole styryl dyes possess a higher second-order hyperpolarizability (β) than the mono-carbazole styryl dyes. An increase in the polarity of the environment causes an increase in the first-order hyperpolarizability (β _CT or β ₀) and second-order hyperpolarizability (γ) of the mono- and bis-carbazole styryl compounds. The NLO properties calculated by the CAM-B3LYP and BHandHLYP functionals show good agreement with the spectroscopic results.     

Pyrazolo[1,5-a]pyrimidine-Dioxaborinine Hybrid Dyes: Synthesis and Substituent Effect in the Photophysical Properties

A novel family of pyrazolo[1,5-a]pyrimidine-dioxaborinine (PP-DB) hybrid dyes was synthesized by the direct construction of the dioxaborinine (DB) fragment on the pyrazolo[1,5-a]pyrimidine (PP) ring, which implies the formation of four new bonds in a one-pot manner. The dyes’ optical properties were investigated and compared with the starting pyrazolo[1,5-a]pyrimidines; a study evidencing large fluorescence quantum yields in products (φ_f up to 69 %) due to an intramolecular charge transfer (ICT) process from the PP core to a ring of DB (PP→DB) that is absent in precursors (φ_f=0.03–0.30). Time-dependent density functional theory (TD-DFT) calculations confirmed the fluorescence process involved in the novel dyes, where their ICT limits the non-radiative process due to the restricted rotation in the D−A system. The present work provides insight into how phenyl and DB ring incorporation impact the optical properties of this new group of hybrids dyes based on PP-DB.     

Novel Metal Complexes Unit of Phenanthroline Derivative for Being Used as Auxiliary Electron Acceptor in Dye Sensitizer Molecules

Donor-acceptor-π bridge-acceptor (D−A−π−A) motif dyes are promising dye sensitizers in dye-sensitized solar cells (DSSCs). In this study, to strengthen with-drawing electron force of the auxiliary electron acceptors(A) in D−A−π−A motif dye sensitizers, the metal complexes unit is be used as auxiliary electron acceptor(A) instead of organic electron-withdrawing monomer. The four polymeric metal complexes were designed, synthesized, and characterized, which used metal complexes of phenanthroline derivatives as auxiliary acceptors (A), benzodithiophene-dithiophene derivatives (BDTT) as donors (D), and 8-hydroxyquinoline derivatives as π-bridges and acceptors of the dye sensitizers, and have been used for dye sensitizers. Under AM 1.5 G (100 mW cm⁻²), the photovoltaic test results indicated that the short-circuit photocurrent density (J_sc) of the DSSCs based four polymeric metal complexes are 11.26, 13.68, 14.42 and 15.57 mA cm⁻² and power conversion efficiency (PCE) are 5.96 %, 7.83 %, 8.07 %, 9.28 % respectively. Both J_sc and PCE value of the four polymeric metal complexes increased in order. This may be due to the fact that larger radius of metal ion under the same change number can enhance the coordination bond and cause stronger electron-withdrawing ability of auxiliary acceptor and stronger charge-transfer ability between the donor and the acceptor, which results in higher J_sc and higher PCE of the polymeric complex dye sensitizer.     

Theoretical investigation of nonlinear optical behavior for rod and T-Shaped phenothiazine based D-π-A organic compounds and their derivatives

The exploration of novel materials with excellent nonlinear optical (NLO) features is an area of frontline investigation for scientific community from technological point of view. This study reports the novel phenothiazine-based rod-shaped and T-shaped NLO molecules which are quantum chemically designed from synthesized compounds: rod-shaped (CFA and CBA) and T-shaped (CTA, CCA and CPA). Structural tailoring was performed on D-π-π-A centered CPA chromophore and the effect of various π-spacers, as well as solvents on NLO response properties is investigated. Density functional theory (DFT) along with time dependent DFT (TDDFT) calculations have been executed at B3LYP/6-311G(d,p) functional to examine entire analysis. Results showed a smaller energy gap in structurally modified compounds as compared to reference CPA. Global reactivity parameters analysis revealed smaller hardness and larger softness values in T-shaped compounds. UV–Vis analysis of investigated molecules displayed a red shift in absorption maximum value as compared to CPA. Natural bond orbital (NBO) and frontier molecular orbital (FMO) analysis revealed the stability and intra-molecular electron transferring (ICT) process in investigated molecules. ICT showed the effective charge shift from donor to acceptor via π-spacers. Overall, promising NLO response exists in gas phase and different solvents (acetonitrile, ethyl alcohol and water). Interestingly, proposed molecule CPP presented a maximum value of linear polarizability < α > as 1518.23 a.u and first hyperpolarizability (β_tot) as 755322.39 a.u in acetonitrile solvent. In short, entitled chromophores exhibited excellent NLO properties due to their lower charge transport resistance. This NLO study may open a new topic for researchers to discover novel NLO for hi-tech submissions of modern era.     

Aromatic/proaromatic donors in 2-dicyanomethylenethiazole merocyanines: from neutral to strongly zwitterionic nonlinear optical chromophores

Push–pull compounds, in which a proaromatic electron donor is conjugated to a 2‐dicyanomethylenethiazole acceptor, have been prepared, and their properties compared to those of model compounds featuring an aromatic donor. A combined experimental (X‐ray diffraction, ¹H NMR, IR, Raman, UV/Vis, nonlinear optical (NLO) measurements) and theoretical study reveals that structural and solvent effects determine the ground‐state polarisation of these merocyanines: whereas 4H‐pyran‐4‐ylidene‐ and 4‐pyridylidene‐containing compounds are zwitterionic and 1,3‐dithiol‐2‐ylidene derivatives are close to the cyanine limit, anilino‐derived merocyanines are essentially neutral. This very large range of intramolecular charge transfer (ICT) gives rise to efficient second‐order NLO chromophores with μβ values ranging from strongly negative to strongly positive. In particular, pyranylidene derivatives are unusual in that they show an increase in the degree of ICT on lengthening the π‐spacer, a feature that lies behind the very large negative μβ values they display. The linking of the formally quinoidal 2‐dicyanomethylenethiazole moiety to proaromatic donors seems a promising approach towards the optimisation of zwitterionic NLO chromophores.     

Highly efficient organic indolocarbazole dye in different acceptor units for optoelectronic applications—a first principle study

A series of novel organic dyes (ICZA1, ICZA2, ICZA3, ICZA4) with D-π-A structural configuration incorporating indolo[3,2,1-jk]carbazole moiety as donor (D) unit, thiophene as π-linker and 2-cyanoacrylic acid as acceptor unit were investigated using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. Indolo[3,2,1-jk]carbazole-based D-π-A dyes composed of different acceptor groups were designed. By modulating acceptor unit, the efficiency of D-π-A dye-based dye-sensitized solar cells (DSSCs) can be further improved. In the present work, four novel push-pull organic dyes only differing in electron acceptor, have been designed based on the experimental literature value of IC-2. In order to further improve the light harvesting capability of indolo[3,2,1-jk]carbazole dyes, the acceptor influence on the dye performance were examined. The NLO property of the designed dye molecules can be derived as polarizability and hyperpolarizability. The calculated value of ICZA2 dye is the best candidate for NLO properties. Furthermore, the designed organic dyes exhibit good photovoltaic performance of charge transfer characteristics, driving force of electron injection, dye regeneration, global reactivity, and light harvesting efficiency (LHE). From the calculated value of ICZA4 dye, it has been identified as a good candidate for DSSCs applications. Finally, it is concluded that the both ICZA2 and ICZA4 dyes theoretically agrees well with the experimental value of IC-2 dye. Hence, the dyes ICZA2 and ICZA4 can serve as an excellent electron withdrawing groups for NLO and DSSCs applications.     

Structural and photophysical studies of triphenylamine-based nonlinear optical dyes: effects of π-linker moieties on the D-π-A structure

In this work, a series of eight metal-free organic dyes based on triphenylamine as a donor and cyanoacetic acid as an acceptor of electrons with the donor-π-acceptor structure were studied by DFT and TD-DFT methods. Their electronic properties, absorption spectra, and molecular nonlinear optical (NLO) responses have been analyzed and reported. The influence of the change of π-conjugated linker on the electrochemical and photophysical properties of these metal-free organic dyes has been investigated and discussed in detail. The energy gap decreases by going from L1 to L8, which causes a large NLO response for the studied dyes. The natural bond orbital (NBO) analysis reveals that the separation of charge occurred upon photoexcitation and the electrons moved from the donor to the acceptor moiety. A high NLO response reveals that this kind of metal-free organic dyes has eye-catching and remarkably large first hyperpolarizability β_tot values, especially for L7 ((E)-2-cyano-3-(3-((E)-2-(3-((E)-4-(diphenylamino)styryl)benzo[c]thiophen-1-yl)vinyl)benzo [c]thiophen-1-yl)acrylic acid) and L8 ((E)-2-cyano-3-(7-((E)-2-(7-((E)-4-(diphenylamino)styryl)thieno[3,4-b]pyrazin-5-yl)vinyl)thieno[3,4-b]pyrazin-5-yl)acrylic acid) with 150423.50 (a.u) and 202773.63 (a.u), respectively. Our research has been carried out to extend the conjugation of organic materials by controlling their π-conjugated linker to design new appealing NLO compounds. This study shows that these dyes are promising and have special properties for modern hi-tech applications such as solar cells, transistors, and organic light-emitting diodes (OLEDs), and even these properties can be adjusted and enhanced by the incorporation of the benzothiophene or thienopyrazine derivatives as a bridge so as to improve from L7 to L8.     

Exploring the effect of different coumarin donors on the optical and photovoltaic properties of azo-bridged push-pull systems: A theoretical approach

We report the theoretical modeling of various azo-bridged coumarin-purpurin systems. The effect of varying the donor (coumarin) part of this D-π-D-π-A system was analyzed in terms of opto-electronic and photovoltaic parameters such as HOMO, LUMO, HOMO-LUMO energy gap, λ_max, light harvesting efficiency, charge injection efficiency, open voltage, reorganization energy by employing density functional theory as incorporated in Gaussian 03 set of codes. The dye-TiO₂ adsorbed systems were also studied using the same level of theory. It was found that just by varying the donor, although of same nature, there is a marked effect on the efficiency parameters of the dye sensitized solar cells based on such dyes. Also, the dye molecules were found to be good sensitizers for TiO₂ semiconductors.     

Substituent Modulation from ESIPT to ICT Emission in Benzoimidazolphenyl-methanones Derivatives: Synthesis,Photophysical and DFT Study

Design and synthesis of five new derivatives of benzophenone based imidazole dyes is presented. Synthesized dyes were well characterized by ¹H NMR, ¹³C NMR, FT-IR and mass analysis. Dyes contain a secondary acceptor, ESIPT core and different donors forming (D-ESIPT core-A) as basic skeleton in order to study both ESIPT and ICT systematically in this same class of dyes. Dyes without a donor substituent showed ESIPT emission while dyes with a substituted strong donor showed intramolecular charge transfer (ICT) emission. Moreover emission properties of methoxy analogue dyes has been studied to further confirm non-ESIPT emission in dyes without donors and ICT emission in strong donor substituted dyes. All dyes exhibited long range emissions from 392 to 567 nm. Dyes exhibiting ESIPT emission showed negative solvatochromism while ICT emission exhibiting dyes shows positive solvatochromism. ICT and ESIPT characteristics are well correlated with polarity functions plots and Mulliken–Hush analysis. Experimental observations are well supported by TD–DFT and computed energies. The electrophilicity index has been calculated to get details of the stabilities of possible tautomers.     

Strongly non-linear optical ferroelectric liquid crystals for frequency doubling

Abstract

From our research for novel non-linear optical (NLO) materials for frequency doublers and optical modulators we report on new ferroelectric liquid crystals, which for the first time, exhibit second order NLO coefficients (for example d ₂₂ = 5 pm V^?1, which are comparable to those of state of the art inorganic NLO materials. The novel compounds contain 5-amino-2-nitrophenyl groups attached close to the chiral centres. The switching behaviour of the new compounds, their spontaneous polarization, as well as their frequency doubling of Nd:YAG laser pulses in the S*_c and in the glass state, are reported. Moreover their waveguiding properties are presented.     

trans/cis‐Isomerization of Fluorene‐Bridged Azo Chromophore with Significant Two‐Photon Absorbability at Near‐Infrared Wavelength

Azo‐containing materials have been proven to possess second‐order nonlinear optical (NLO) properties, but their third‐order NLO properties, which involves two‐photon absorption (2PA), has rarely been reported. In this study, we demonstrate a significant 2PA behavior of the novel azo chromophore incorporated with bilateral diphenylaminofluorenes (DPAFs) as a π framework. The electron‐donating DPAF moieties cause a redshifted π–π* absorption band centered at 470 nm, thus allowing efficient blue‐light‐induced trans‐to‐cis photoisomerization with a rate constant of 2.04×10^?1 min^?1 at the photostationary state (PSS). The open‐aperture Z‐scan technique that adopted a femtosecond (fs) pulse laser as excitation source shows an appreciably higher 2PA cross‐section for the fluorene‐derived azo chromophore than that for common azobenzene dyes at near‐infrared wavelength (λ_ex=800 nm). Furthermore, the fs 2PA response is quite uniform regardless of the molecular geometry. On the basis of the computational modeling, the intramolecular charge‐transfer (ICT) process from peripheral diphenylamines to the central azo group through a fluorene π bridge is crucial to this remarkable 2PA behavior.     

Enhanced third‐order nonlinear optical properties determined in thin films using the Z‐scan technique: bis(μ‐4,4′‐oxydibenzoato)bis[(4′‐phenyl‐2,2′:6′,2′′‐terpyridine)cobalt(II)]

π‐Conjugated organic materials exhibit high and tunable nonlinear optical (NLO) properties, and fast response times. 4′‐Phenyl‐2,2′:6′,2′′‐terpyridine (PTP) is an important N‐heterocyclic ligand involving π‐conjugated systems, however, studies concerning the third‐order NLO properties of terpyridine transition metal complexes are limited. The title binuclear terpyridine Co^II complex, bis(μ‐4,4′‐oxydibenzoato)‐κ³O,O′:O′′;κ³O′′:O,O′‐bis[(4′‐phenyl‐2,2′:6′,2′′‐terpyridine‐κ³N,N′,N′′)cobalt(II)], [Co₂(C₁₄H₈O₅)₂(C₂₁H₁₅N₃)₂], (1), has been synthesized under hydrothermal conditions. In the crystal structure, each Co^II cation is surrounded by three N atoms of a PTP ligand and three O atoms, two from a bidentate and one from a symmetry‐related monodentate 4,4′‐oxydibenzoate (ODA²⁻) ligand, completing a distorted octahedral coordination geometry. Neighbouring [Co(PTP)]²⁺ units are bridged by ODA²⁻ ligands to form a ring‐like structure. The third‐order nonlinear optical (NLO) properties of (1) and PTP were determined in thin films using the Z‐scan technique. The title compound shows a strong third‐order NLO saturable absorption (SA), while PTP exhibits a third‐order NLO reverse saturable absorption (RSA). The absorptive coefficient β of (1) is −37.3 × 10⁻⁷ m W⁻¹, which is larger than that (8.96 × 10⁻⁷ m W⁻¹) of PTP. The third‐order NLO susceptibility χ⁽³⁾ values are calculated as 6.01 × 10⁻⁸ e.s.u. for (1) and 1.44 × 10⁻⁸ e.s.u. for PTP.     

Computational studies on optoelectronic and charge transfer properties of some perylene‐based donor‐π‐acceptor systems for dye sensitized solar cell applications

We report DFT studies on some perylene‐based dyes for their electron transfer properties in solar cell applications. The study involves modeling of different donor‐π‐acceptor type sensitizers, with perylene as the donor, furan/pyrrole/thiophene as the π‐bridge and cyanoacrylic group as the acceptor. The effect of different π‐bridges and various substituents on the perylene donor was evaluated in terms of opto‐electronic and photovoltaic parameters such as HOMO‐LUMO energy gap, λ_max, light harvesting efficiency(LHE), electron injection efficiency (Ø_inject), excited state dye potential (E^dye*), reorganization energy(λ), and free energy of dye regeneration (). The effect of various substituents on the dye–I₂ interaction and hence recombination process was also evaluated. We found that the furan‐based dimethylamine derivative exhibits a better balance of the various optical and photovoltaic properties. Finally, we evaluated the overall opto‐electronic and transport parameters of the TiO₂‐dye assembly after anchoring the dyes on the model TiO₂ cluster assembly.     

Synthesis and characterization of interpenetrating polymer networks with nonlinear optical properties

We report the synthesis and characterization of interpenetrating polymer networks (IPNs) exhibiting nonlinear optical (NLO) properties. The network consists of aliphatic polycarbonate urethane (PCU) and poly(methyl methacrylate-co-N,N-disubstituted urea), with a nonlinear optical (NLO) chromophore incorporated into N,N-disubstituted urea. The full IPNs have only one T_g, as determined by differential scanning calorimetry (DSC), together with scanning electron microscopy (SEM) observations, suggest a single phase morphology. The thin films of IPNs are transparent and the unpoled samples produced second harmonic generation (SHG) signals at room temperature. This result indicates that the NLO chromophore is oriented noncentrosymmetrically during the IPN formation process and is tightly held between the permanent entanglements of the two component networks of the IPN. © 1996 John Wiley & Sons, Inc.     

四硫富瓦烯作为染料敏化太阳能电池有机染料电子给体的理论研究

为了研究四硫富瓦烯(TTF)基团对有机染料敏化剂光电性能的影响,以咔唑染料Dye 1 为原型,引入TTF基团作为电子给体,设计了咔唑染料Dye 2. 采用密度泛函理论(DFT)和含时密度泛函理论(TD-DFT)分别计算模拟了纯染料分子和吸附团簇(TiO₂)₉后的形貌、分子轨道能级以及紫外-可见吸收光谱,采用周期性密度泛函理论计算模拟染料分子在二氧化钛(101)面吸附的表面形貌. 结果发现：在有机染料中引入TTF基团有助于有机染料敏化剂在二氧化钛表面的抗团聚作用和分子内的电荷转移;最为重要的是,TTF 基团的强给电子能力极大地增强了有机染料敏化剂的光捕获能力. 所有的计算结果表明,TTF基团是一种非常有潜力改善染料敏化剂光电性能的给电子基团.     

Extended Alkenyl and Alkynyl Benzotriazoles with Enhanced Two-Photon Absorption Properties as a Promising Alternative to Benzothiadiazoles

A series of donor–π–acceptor–π–donor (D -π-A-π-D) benzoazole dyes with 2H-benzo[d][1,2,3]triazole or BTD cores have been prepared and their photophysical properties characterized. The properties of these compounds display remarkable differences, mainly as a result of the electron-donor substituent. Dyes with the best properties have visible-light absorption over λ=400 nm, large Stokes shifts in the range of about 3500–6400 cm⁻¹, and good fluorescence emission with quantum yields of up to 0.78. The two-photon absorption properties were also studied to establish the relationship between structure and properties in the different compounds synthesized. These results provided cross sections of up to 1500 GM, with a predominance of S₂←S₀ transitions and a high charge-transfer character. Time-dependent DFT calculations supported the experimental results.