Experimental and theoretical approaches to understanding two-photon absorption spectra in polymethine and squaraine molecules

Fu, Jie; Padilha, Lázaro A.; Hagan, David J.; Stryland, Eric W. Van; Przhonska, Olga V.; Bondar, Mykhailo V.; Slominsky, Yuriy L.; Kachkovski, A.D.

doi:10.1364/josab.24.000067

Cited by 70 publications

(110 citation statements)

References 25 publications

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“…The nature of the short wavelength 2PA band can be analyzed using the simplest three-level energy model 74 based on the sum-over-states (SOS) approach, 53 when δ 2PA is determined by the expression: 75 with an extremely large maximum extinction coefficient ε(λ ab max ) ∼ 10 6 M −1 cm −1 . Also, the relatively small detuning energy, ΔE = E 01 − E P , leads to intermediate state resonance enhancement (ISRE), 76 and a corresponding "double resonance" excitation condition 77 for the S 0 →S n two-photon transition when E 0n = 2E P . Apparently, these parameters are mainly responsible for so large a two-photon cross section δ 2PA in the short wavelength 2PA band of 1.…”

Section: Methodsmentioning

confidence: 99%

Linear Photophysics and Femtosecond Nonlinear Spectroscopy of a Star-Shaped Squaraine Derivative with Efficient Two-Photon Absorption

et al. 2016

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The synthesis, comprehensive linear photophysical and photochemical study, two-photon absorption (2PA) spectrum, ultrafast relaxation kinetics in the excited states, and efficient superluminescence properties of a new symmetrical three-armed star-shaped squaraine derivative (1) are presented. The steady-state spectral parameters of 1 in a number of organic solvents, including fluorescence excitation anisotropy spectra, revealed a weak interaction between the squaraine branches and the effect of symmetry breaking in the ground electronic state. The degenerate 2PA spectrum of 1 was obtained over a broad spectral range with a maximum cross section of ∼8000 GM using the open aperture Z-scan technique. The nature of the fast dynamic processes in the excited electronic states of 1 was investigated by the femtosecond transient absorption pump−probe method, revealing characteristic relaxation times of ∼3−4 ps. The efficient superluminescence emission of 1 was observed in relatively low concentration solution (≈ 2.3·10 −4 M) under femtosecond transverse pumping. A quantum-chemical study of 1 was performed using ZINDO/S//DFTB theory levels. Simulated 1PA and 2PA absorption spectra were found to be in a good agreement with experimental data. The figure of merit for 1 is ∼10 11 GM, 1 one of the highest values ever reported for two-photon fluorescence molecular probes, suggesting strong potential for its application in two-photon fluorescence microscopy and bioimaging.

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Section: Methodsmentioning

confidence: 99%

Linear Photophysics and Femtosecond Nonlinear Spectroscopy of a Star-Shaped Squaraine Derivative with Efficient Two-Photon Absorption

et al. 2016

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“…Dicyanoyinyl groups have been found to enhance TPA cross-section due to the presence of delocalized electrons in the dicyanoyinyl bond. [73][74][75] We are interested in finding the contribution of each conjugation unit in each of the polymer chain to the TPA cross-section. Bhatta et al 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 and 6.34 × 10 4 GM respectively.…”

Section: Equationmentioning

confidence: 99%

Effect of Acceptor Strength on Optical and Electronic Properties in Conjugated Polymers for Solar Applications

et al. 2015

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Four new low-bandgap electron-accepting polymers-poly(4,10-bis(2-butyloctyl)-2-(2-(2-ethylhexyl)-1,1-dioxido-3-oxo-2,3-dihydrothieno[3,4-d]isothiazol-4-yl)thieno[2',3':5,6]pyrido[3,4-g]thieno[3,2-c]isoquinoline-5,11(4H,10H-dione) (PNSW); poly(4,10-bis(2-butyloctyl)-2-(5-(2-ethylhexyl)-4,6-dioxo-5,6-dihydro-4H-thieno[3,4-c]pyrrol-1-yl)thieno[2',3':5,6]pyrido[3,4-g]thieno[3,2-c]isoquinoline-5,11(4H,10H)-dione) (PNTPD); poly(5-(4,10-bis(2-butyloctyl)-5,11-dioxo-4,5,10,11-tetrahydrothieno[2',3':5,6]pyrido[3,4-g]thieno[3,2-c]isoquinolin-2-yl)-2,9-bis(2-decyldodecyl)anthra[2,1,9-def:6,5,10-d'e'f']diisoquinoline-1,3,8,10(2H,9H)-tetraone) (PNPDI); and poly(9,9-bis(2-butyloctyl)-9H-fluorene-bis((1,10:5,6)2-(5,6-dihydro-4H-cyclopenta[b]thiophene-4-ylidene)malonitrile)-2-(2,3-dihydrothieno[3,4-b][1,4]dioxine)) (PECN)-containing thieno[2',3':5',6']pyrido[3,4-g]thieno[3,2-c]isoquinoline-5,11(4H,10H)-dione and fluorenedicyclopentathiophene dimalononitrile, were investigated to probe their structure-function relationships for solar cell applications. PTB7 was also investigated for comparison with the new low-bandgap polymers. The steady-state, ultrafast dynamics and nonlinear optical properties of all the organic polymers were probed. All the polymers showed broad absorption in the visible region, with the absorption of PNPDI and PECN extending into the near-IR region. The polymers had HOMO levels ranging from -5.73 to -5.15 eV and low bandgaps of 1.47-2.45 eV. Fluorescence upconversion studies on the polymers showed long lifetimes of 1.6 and 2.4 ns for PNSW and PNTPD, respectively, while PNPDI and PECN showed very fast decays within 353 and 110 fs. PECN exhibited a very high two-photon absorption cross section. The electronic structure calculations of the repeating units of the polymers indicated the localization of the molecular orbitals in different co-monomers. As the difference between the electron affinities of the co-monomers in the repeating units decreases, the highest occupied and lowest unoccupied molecular orbitals become more distributed. All the measurements suggest that a large difference in the electron affinities of the co-monomers of the polymers contributes to the improvement of the photophysical properties necessary for highly efficient solar cell performance. PECN exhibited excellent photophysical properties, which makes it to be a good candidate for solar cell device applications.

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“…As Grahn et al42, 43 have shown some years ago, oligomerization of squaraines leads to even smaller band gaps which would allow harvesting of low‐energy sunlight 36. However, since the S 2 state in squaraines is forbidden by symmetry, there is a decent gap of absorption at higher energies 44…”

Section: Introductionmentioning

confidence: 99%

Polymeric Squaraine Dyes as Electron Donors in Bulk Heterojunction Solar Cells

Völker

Uemura

Limpinsel

et al. 2010

Macro Chemistry & Physics

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A polysquaraine low band gap polymer was synthesized by Yamamoto coupling of a monomeric dibromo indolenine squaraine dye. The resulting polymer has a weight average molar mass in the order of M w ∼30.000-50.000 and a polydispersity of ca. 1.7 as determined by gel-permeation chromatography (GPC). The electronic properties of monomer and polymer were investigated by cyclic voltammetry, absorption and emission spectroscopy. Owing to exciton coupling the absorption bands of the polymer are red-shifted and strongly broadened compared to the monomer squaraine dye. Bulk heterojunction solar cells were prepared from blends of the polysquaraine with the fullerene derivative [6,6]-phenyl C61-butyric acid methyl ester (PCBM) in different weight ratios (1:3 to 1:1). The power conversion efficiencies under simulated AM 1.5 conditions yielded 0.45 % for these non-optimized systems. The external quantum efficiency (EQE) shows that the photoresponse spans the range from 300 to 850 nm, which illustrates the promising properties of this novel organic semiconductor as a low band gap donor material in organic photovoltaics.

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Experimental and theoretical approaches to understanding two-photon absorption spectra in polymethine and squaraine molecules

Cited by 70 publications

References 25 publications

Linear Photophysics and Femtosecond Nonlinear Spectroscopy of a Star-Shaped Squaraine Derivative with Efficient Two-Photon Absorption

Linear Photophysics and Femtosecond Nonlinear Spectroscopy of a Star-Shaped Squaraine Derivative with Efficient Two-Photon Absorption

Effect of Acceptor Strength on Optical and Electronic Properties in Conjugated Polymers for Solar Applications

Polymeric Squaraine Dyes as Electron Donors in Bulk Heterojunction Solar Cells

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