Intramolecular Cooperative and Anti-Cooperative Effect on the Two

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Spectroscopy and Photochemistry; General Theory

Intramolecular Cooperative and Anti-Cooperative Effect on the TwoPhoton Absorption Cross Section in Triphenylamine Derivatives Ruben D. Fonseca, Marcelo Gonçalves Vivas, Daniel Luiz Silva, Gwenaelle Eucat, Yann Bretonnière, Chantal Andraud, Cleber Renato Mendonca, and Leonardo De Boni J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.9b00518 • Publication Date (Web): 08 Apr 2019 Downloaded from http://pubs.acs.org on April 8, 2019

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The Journal of Physical Chemistry Letters

Intramolecular Cooperative and Anti-Cooperative Effect on the Two-Photon Absorption Cross Section in Triphenylamine Derivatives Ruben D. Fonseca1,2, Marcelo G. Vivas3, Daniel Luiz Silva4, Gwenaelle Eucat5, Yann Bretonnière5, Chantal Andraud5, Cleber R. Mendonca1, Leonardo De Boni1 1Instituto 2Universidad 3Laboratório

de Física de São Carlos, Universidade de São Paulo, 13560-970, São Carlos, SP, Brazil

popular del Cesar, Departamento de Fisica, Barrio Sabana, 2000004, Valledupar, Cesar, Colombia

de Espectroscopia Óptica e Fotônica , Universidade Federal de Alfenas, Poços de Caldas, MG, Brazil

4Departamento

de Ciências da Natureza, Matemática e Educação, Universidade Federal de São Carlos, Rod. Anhanguera – Km 174,13600-970 Araras, SP, Brazil

5Univ

Lyon, Ens de Lyon, CNRS UMR 5182, Université Claude Bernard Lyon 1, Laboratoire de Chimie, F69342, Lyon, France [email protected] and [email protected]

Abstract The intramolecular cooperative effect in branched molecules is a consequence of the interaction and extent of electronic coupling among the different axes of charge transfer. Such effect is the key to obtain remarkable nonlinear optical response in molecular systems. Here we show that triphenylamine derivative molecules containing only two branches present strongest electronic interaction between them at the excited state, generating exponential enhancement of the 2PA cross section. The primary factor for such behavior was ascribed to the substantial extent and interaction of the π-electron delocalization promoted by the strong electron-donating and acceptor anti-symmetrical groups present in each branch. On the other hand, for the three-branch molecules we observed an anti-cooperative effect, i. e., the 2PA cross section decreases as compared to the one-branch structure as we normalized the signal by the effective π-electron number in each molecule.

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The understanding, at the molecular level, of the underlying mechanism that rules the enhancement of the nonlinear optical response in organic materials is primordial for the development of novel photonic/organic devices. 1-12 In the last few decades, different types of molecular systems have been proposed to increase the two-photon absorption (2PA) cross section, among which are the incorporation of symmetrical donor/acceptor groups13 or the increase of conjugation length.14-15 In general, however, such strategies lead only to additive effects, in which the 2PA cross section increases quadratically with the number of π-electron and it is related to a single 2PA allowed excited state, which restricts the spectral range of excitation. Moreover, the 2PA cross section tends to saturate quickly. To overcome this limitation, multi-branched molecules have been synthesized as an alternative molecular design, with the aim of enhancing nonlinear effects. 16-17 These molecules may have V-shaped designs (A-π-D-π-A or D-π-A-π-D), designs ((D-π-A)3),

21-24

18-20

octupolar

and dendritic structures of high generations ((D-π-A)n),25-30

where D and A refer to the electron-donating and electron-withdrawing groups (EWG), respectively, linked through a bridge of π-conjugated bonds. These multi-branched structures may exhibit a strong cooperative effect among its branches, generating a significant enhancement (up to exponential increase) of their optical properties. 31-33 As reported in Ref.34, the cooperative effect results from the interaction and extent of electronic coupling among the different axes of charge transfer in multi-branched systems and is crucial to obtain a high nonlinear optical response. These properties are closely associated with the charge transfer from the core to the periphery group (or vice versa) via strong electron donor and acceptor groups, as well as the electron interaction among the branches at the excited state.35-37 These effects, in triphenylamine derivatives, for example, depend on the dihedral angle between the planes containing the phenyl ring on one side and the nitrogen-bonded carbon atoms on the other side. The core may promote low electronic coupling among the branches, decreasing the nonlinear optical effect. As results, we can even find smaller 2PA cross section in octupolar than in dipolar molecules. 37 The molecules studied here are composed by triphenylamine, in which different branches are attached. The number of branches in the molecules was disposed in such a way to obtain dipolar, V-shaped and octupolar geometries. Figure 1 displays, in the first row, triphenylamine derivatives containing cyanobenzene arranged in one-branch (CN-1



dipolar structure), two-branch (CN-2 V-shaped structure) and three-branch (CN-3 octupolar structure); this group was named as CN. In the second row of Fig. 1, it is shown the group named CNS that contains only one dipolar molecule (CNS-1), which is a triphenylamine attached to cyanopyridine. The third row contains two molecules formed by triphenylamine attached to cyanonitrobenzene, organized in dipolar (CN𝑶𝟐-1) and Vshaped (CN𝑶𝟐-2) geometries. Finally, in the last row, it is displayed the triphenylamine derivatives containing dicyanobenzene groups arranged in one-branch (2CN-1 dipolar structure), two-branch (2CN-2 V-shaped structure) and three-branch (2CN-3 octupolar structure). Also, in Fig. 1 the molecules were arranged such that they are displayed from the weakest to the strongest electron-withdrawing group (EWG), indicated by the arrow. Although we have called the two and three-branch molecules as V-shaped and octupolar structures, in fact, these types of molecules also present a high dipolar contribution, as it will be shown along this paper. In addition, Neff represents the effective number of πelectrons evaluated according Ref.

38.

Details about molecules syntheses are found

elsewhere. 39-40 Figure 2 depicts the steady-state absorption (solid lines, right axis) for molecules of the group CN (first row), CNS (second row), CNO2 (third row) and 2CN (fourth row). All molecules present an intense absorption in the near UV-visible region, with molar absorptivity in the order of 104 L·mol-1·cm-1 (M-1·cm-1). To further understand the electronic structure and branching effect on these molecules, we performed quantum chemical calculations based on the DFT framework. Details about it can be found in the “Supporting information - SI”. Based on these results, we calculated the dipole moment transition (μ) and permanent dipole moment difference (Δμ), which rules the 2PA cross section in noncentrosymmetric molecules. The results are reported in Table 1. It is observed that the branching effect tends to slightly increase the permanent dipole moment difference between the first excited and ground states (Δμ01), contributing to improve the charge separation along the branches. Therefore, this result shows that although some molecules present V-shaped and octupolar structures, its dipolar contribution is strong and, therefore, the 2PA spectra for these molecules should contain a lowest-energy 2PA band with considerable magnitude. According to spectroscopic data (see SI), the lowest-energy band observed in the experimental absorption spectra is related to a charge-transfer transition from the triphenylamine core (donating group) to the EWG branch, for all molecules. Also, we ACS Paragon Plus Environment

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identified a split of the lowest-energy band due to two nondegenerate (CN-2, CNO2-2, 2CN-2 molecules) or two degenerate (CN-3 and 2CN-3 molecules) charge-transfer states (see Fig. SI-1). Recently, multi-branching effect in organic molecules have been interpreted according to the Frenkel exciton model,31, 41 which predicts that the lowestenergy band for two-branch molecules (CN-2, CNO2-2, 2CN-2) results from a split of the first excited state of each dipolar molecule (CN-1, CNO2-1, 2CN-1) in two excited states separated by 2 V, in which V is an electronic coupling parameter between the branches. Therefore, 2V is the energy difference between the two first excited states in two-branch molecules. In this context, we used Gaussian decomposition to obtain the energy separation between the peak and the shoulder in the absorption spectrum of molecules CN-2, CNO2-2, and 2CN-2, and found, respectively, VCN-2 = 170 meV, VCNO22

= 132 meV and V2CN-2 = 122 meV. According to the Frenkel exciton model, the split

should be symmetrical with respect to the first excited state of the dipolar molecules (CN1, CNO2-2, and 2CN-2). From the difference in energy between the peaks of the lowest energy band for dipolar and V-shaped molecules, we obtained, respectively, VCN-2 = 190 meV, VCNO2-2 = 112 meV and V2CN-2 = 115 meV. Such values are in good agreement with the ones derived from the Gaussian decomposition. For the octupolar molecules (three-branch), the Frenkel model predicts that the first excited state is degenerate, i.e., S1 and S2 excited states present the same energy. Also, the S3 state energy (not 1PA allowed but strongly 2PA allowed) undergoes a displacement of 2V, as compared to the lowest energy state present in dipolar molecules. In fact, our DFT calculations (see Table SI-1) show that S1 and S2 states are degenerate for the octupolar molecules (CN-3 and 2CN-3) and that S3 state is strongly 2PA allowed (see Table SI-2) and forbidden by 1PA (see Table SI-1). However, the S3 state does not present displacement of 2V with respect to the S1 state of the dipolar (CN-1 and 2CN-1) molecules. According to the Frenkel’s exciton model,42 the interaction between the branches at the excited state for a two-branch molecule provides an increase of the μ01 and Δμ01 dipoles moment, i.e., μ012-branch= (3/2)1/2 μ011-branch and Δμ012-branch= (3)1/2/2 Δμ011-branch. Proceeding in this way, we found μ01= 6.6 D (μ01exp=6.5 ± 0.5 D), μ01= 6.6 D (μ01exp= 5.8 ± 0.5 D) and μ01= 6.6 D (μ01exp= 8.8 ± 0.5 D) for CN-2, CNO2-2 and 2CN-2 respectively. At the same time, we obtained Δμ01=8.2 D (Δμ01exp= 11.8 ± 1.4 D), Δμ01= 8.1 D (Δμ01exp= 10.0 ± 0.7 D) and Δμ01=8.7 D (Δμ01exp= 9.5 ± 0.7 D) for CN-2, CNO2-2 and 2CN-2 respectively. Therefore, a good agreement is found for the V-shaped molecules.



Regarding the octupolar molecules, the Frenkel Exciton model predicts that μ01 and Δμ01 are √3 and √2/2 times the values of the one-branch molecules (μ013-branch = (3)1/2μ011-branch and Δμ013-branch= (2)1/2/2 Δμ011-branch). Thus, we found μ01=9.3 D (μ01exp=5.6 ± 1.0 D) for both CN-3 and 2CN-3 molecules, while for Δμ01, we obtained Δμ01=6.7 D (Δμ01exp=12.5 ± 0.9 D) for CN-3 and Δμ01=7.1 D (Δμ01exp=10.6 ± 1.1 D) for 2CN-3. Such results about the dipole moment disagree with the Frenkel Exciton model; specifically, the model tends to underestimate the dipole moment values (μ01 and Δμ01) for the multi-branched molecules studied here. Exception found only for μ01 in octupolar molecules, in which the model overestimated the values. In Fig. 2, the open circles (left axis) represent the experimental 2PA cross section spectra for molecules of the group CN (first row), CNS (second row), CNO2 (third row) and 2CN (fourth row), determined by performing open-aperture Z-scan measurements with femtosecond pulses. The first general aspect to be highlight is that molecules with the same structure exhibit an increase of the 2PA cross section as a function of the EWG strength (or the number of effective π-electron). For example, we obtained for the dipolar structures 2PA cross sections, corresponding to the peak of the lowest-energy 2PA allowed band, of (1.3 ± 0.2)  102 GM for CN-1 at 840 nm, (1.6 ± 0.2)  102 GM at 900 nm for CNS-1, (2.2 ± 0.3)  102 GM at 900 nm for CNO2-1 and (3.8 ± 0.6)  102 GM at 1000 nm for 2CN-1. For V-shaped structures that contain two 2PA allowed bands, we found the same behavior for the bands, i. e., σ2PALE = (1.3 ± 0.2)  102 GM for the lowestenergy (LE) 2PA band (at 910 nm) and σ2PAHE = (3.0 ± 0.5)  102 GM for higher-energy (HE) 2PA band (at 800 nm) for CN-2; σ2PALE = (1.9 ± 0.3)  102 GM at 960 nm and σ2PAHE = (4.0 ± 0.6)  102 GM at 850 nm for CNO2-2; and σ2PALE = (2.9 ± 0.4)  102 GM at 1100 nm and σ2PAHE = (12 ± 2)  102 GM at 960 nm for 2CN-2. For octupolar structures, we observed two 2PA bands with cross sections of (σ2PALB = 1.8 ± 0.3)  102 GM at 880 nm and (σ2PAHB = 2.6 ± 0.4)  102 GM at 710 nm for CN-3 and only one 2PA allowed band for 2CN-3. In fact, for molecule 2CN-3, we observed a broad 2PA allowed band located at 1010 nm with 2PA cross section of σ2PA = (4.2 ± 0.6)  102 GM, indicating the presence of another 2PA allowed excited state, as pointed out by the DFT calculations (see closed circles in Fig. 2 (i)). Indeed, as shown in the results of DFT calculations (Fig 2 and Table SI-2), the energy difference between the degenerated states (S1 and S2) and the strongly allowed 2PA state (S3) is 0.79 eV for CN-3 and 0.50 eV for 2CN-3, which corresponds to an electronic coupling constant V= 263


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meV and V = 166 meV, respectively. However, according to the experimental results (see open circles in Fig. 2 (c) and (i)), these values are smaller, i.e., 0.68 eV (V= 226 meV) for CN-3 and only ~0.30 eV (V= 100 meV) for 2CN-3. Because of this, the split of the 2PA band for the 2CN-3 molecule is not clearly observed. Regarding the 2PA cross section, if the 2PA cross section of the two 2PA bands of the CN-3 molecule are added, a similar result to the one obtained for the 2CN-3 molecule is found. The blue lines in Fig. 2 show the simulated 2PA spectra. Such simulated spectra were modeled based on the information (transition energies and 2PA transition probabilities reported in SI) provided by the quadratic DFT calculations and the linewidths estimated through the fitting of the experimental 2PA spectra. The results of the DFT calculations confirm that 2PA selections rules are relaxed for all molecules. In addition, it can be observed good agreement between theoretical (blue) and experimental (open symbols) results for the 2PA cross sections and spectral positions, except for the CN-3, CNO2-2 and 2CN-3. Figure 3 illustrates the 2PA cross section for molecules with the same geometry as a function of the increase of effective number of π-electrons. Such parameter is calculated by geometrically weighting the number of electrons in each conjugated path of the molecule, i.e., N eff 

 Ni2 ,

where Ni is the number of π-electron of the

i

molecule within and outside the conjugation length. More details can be found in Ref. 38. In summary, the 2PA cross section exhibits a quadratic increase for the dipolar molecules (circles), exponential for the higher-energy 2PA band of the V-shaped molecules (squares) and a linear increase for the lowest-energy 2PA band for V-shaped (up triangles), while for octupolar molecules (diamonds) a slight increase is observed. To better understand the 2PA cross section results for the molecules with different geometries, we have used the 2PA Figure of Merit (2PA-FOM) defined as σ2PAFOM =σ2PA/Neff2, because the 2PA cross section scale as the fourth power of dipole moment. Thus, we can discriminate among the anti-cooperative (σ2PAFOM (HE, branching) < σ2PAFOM (dipolar)), additive (σ2PAFOM (HE, branching) = σ2PAFOM (dipolar)) and cooperative (σ2PAFOM (HE, branching) > σ2PAFOM (dipolar)) effects. Proceeding in this way, we found for dipolar molecules σ2PAFOM =0.50 GM for CN-1, σ2PAFOM =0.50 GM for CNS-1, σ2PAFOM =0.56 GM for CNO2-1 and σ2PAFOM =0.80 GM for 2CN-1. For Vshaped molecules, the values are σ2PAFOM (LE) = 0.30 GM and σ2PAFOM (HE) = 0.70 GM for CN-2, σ2PAFOM (LE) = 0.32 GM and σ2PAFOM (HE) = 0.68 GM for CNO2-2; σ2PAFOM



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(LE) = 0.34 GM and σ2PAFOM (HE) = 1.41 GM for 2CN-2. Finally, we obtained σ2PAFOM (LE) = 0.30 GM and σ2PAFOM (HE) = 0.44 GM for CN-3. However, it was not possible to obtain this parameter for the 2CN-3 molecule due to the small energy difference among the first three excited states. Nevertheless, even considering that the S3 excited state has 2PA cross section much higher than the S1 and S2 states (as pointed out through the theoretical calculations), the σ2PAFOM (HE) for the octupolar molecule (2CN-3) is still lower than σ2PAFOM for 2CN-1 (dipole molecule). As seen, the branching effect tends to decrease the 2PA cross section to the lowest energy 2PA band (dipolar character) and enhances the higher-energy 2PA band (V-shaped or octupolar character), redistributing the 2PA cross section along the spectrum of the multi-branching molecules. Another important aspect to highlight is that for CN-2 and CNO2-2 molecules, the 2PA-FOM cross section related with the branching effect (higher-energy 2PA band) increase 1.40 times when compared to the 2PA band of the dipolar molecules, while for 2CN-2 (strongest EWG strength), we observed an increase of 1.76 times. Therefore, for these structures (V-shaped), the cooperative effect between the branches is achieved and strongly dependent on the EWG strength. On the other hand, for the octupolar structures, the 2PA-FOM for both 2PA bands tends to decrease when compared to the dipolar structure due, most probably, to their weak electronic coupling, causing an anticooperative effect. Such outcomes show that (i) for V-shaped structures, strong EWG groups are of major importance to reach an effective cooperative effect between the branches (and not necessarily the electronic coupling parameter), while (ii) for octupolar structures, a higher electronic coupling parameter is vital to reach higher 2PA cross section as reported in Ref. 42. Indeed, according to the Frenkel exciton model, the 2PA cross section for the lowest energy (LE) and higher energy (HE) 2PA allowed bands of octupolar molecules can be predicted from the dipolar structure as: *, gf  2LE PA   2 PA

*, gf  2HE PA   2 PA

(1)

2 E gf

 Egf  V 

2

2 2 E gf

 Egf  4V 

2

,

(2)

in which  2*,PAfg and Egf, are, respectively, the 2PA cross section for the dipolar molecules and the transition energy for octupolar molecules. By using Eqs. (1-2), we found for CNLE 2 3,  2 PA  1.58  10 GM while we experimentally obtained σ2PALE = (1.8 ± 0.3) × 102 GM


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HE 2 (see Fig. 3 (c)); and  2 PA  4.88  10 GM for higher energy 2PA band while we

experimentally obtained σ2PAHE = (2.6 ± 0.4) × 102 (see Fig. 3 (c)). For 2CN-3 the Frenkel LE 2 HE 3 exciton model predicts  2 PA  4.08  10 GM and  2 PA  1.00  10 GM . As previously

explained, we found only one 2PA allowed band for this molecule with 2PA cross section of σ2PA = (4.2 ± 0.6) × 102 GM. In conclusion, the exponential increase of the 2PA cross section obtained can be ascribed to the great charge redistribution at the excited state between the branches due to the strong A-π-D-π-A anti-symmetrical V-shaped arrangement, while the anticooperative effect can be attributed to the low electron coupling parameter in the octupolar (A-π-D)3 configuration. Most probably, this configuration generated an undesirable effect on the 2PA cross section occasioning a small excited state transition dipole moment or a negative interference term on the 2PA.43-44 Furthermore, we see that the multi-branching effect tends to redistribute the 2PA cross section along the entire nonlinear spectrum, which is essential for several applications.

ACKNOWLEDGMENTS Financial support from FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo, grants 2011/12399-0, 2015/20032-0 and 2016/20886-1), FAPEMIG (Fundação de Amparo à Pesquisa do Estado de Minas Gerais, grant APQ-01203-16), CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico, grant 425180/2018-2), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) and the Air Force Office of Scientific Research (FA9550-15-1-0521) are acknowledged.

Supporting Information: Details about the experimental methods, computational details, absorption spectra, fluorescence spectra, dipole moment calculations, solvatochromic Stokes shift measurements, one- and two-photon absorption theoretical calculations are reported.

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Page 14 of 18

Page 15 of 18

Figures

Dipolar Neff=16.4

EWG strength

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


Octupolar

V-shaped Neff=20.7

Neff=24.2

Neff=18.1

Neff=19.9

Neff=21.7

Neff=24.2

Neff=28.9

Neff=34.6

Figure 1. Chemical structures of one-branch or dipolar (𝐂𝐍𝐒 ― 𝟏, 𝑪𝑵𝑶𝟐 ― 𝟏, 𝟐𝑪𝑵 ― 𝟏 and 𝑪𝑵 ― 𝟏), twobranch V-shaped (𝑪𝑵𝑶𝟐 ― 𝟐,𝟐𝑪𝑵 ― 𝟐 and 𝑪𝑵 ― 𝟐) and three-branch octupolar (𝟐𝑪𝑵 ― 𝟑 and 𝑪𝑵 ― 𝟑). Neff represents the effective number of π-electrons evaluated according Ref. 38.



CN-2

(a)

CN-1

500

Octupolar

V-shaped

Dipolar 600

(b)

CN-3 (c)

5 4

400

3

300

1

2PA cross section (GM)

100 0

CNO2-2

500

0

(f) 4

400

3

2PA(theo)/2

300

2

200

1

100 0

CNO2-1

500

(e)

0

CNO2-2

5

(f)

4

400

3

2PA(theo)/2

300

2

200

1

100 0

2CN-2 (h)

2CN-1 (g)

500

0

2CN-3 (i)

5 4

2PA(exp)/2

400

2PA(theo)/2

2PA(theo)/2

Molar absorptivity (104 M-1cm-1)

2

200

3

300 2 200 1

100

Dipolar

5

CN-1 (a)

0 Quadrupolar 600 750

CN-2 (b)

900

Octupolar 1050 1200 5 CN-3 (c)

750

900

1050

1200

600

750

900

1050

1200

0 1350

Excitation wavelength (nm) 3

3

2

2

1

1

Figure 2 – Open circles ( , left axis) represent the experimental 2PA cross section, while the solid black 0

0

CNS-1 (d)

line (

3

Theoretical spectrum ,1PA right axis) shows the 1PA cross section spectra of all molecules dissolved in chloroform. solid

Oscillator Strength

4

Normalized fluorescence

blue lines (1PA transitions , blue) (DFT) represent the simulated 2PA spectra based on the information (transition energies

2 1

and 2PA transition ) provided by the quadratic RF calculations. Theoretical (Fig. 2 (f), (g) CNO -2 (f) probabilities,

0

CNO2-1 (e)

4

4

3

2

1

results.

1

0

0

2

and (i)) and experimental (Fig. 2 (h)) 2PA cross sections were divided by 2 for better visualization of the

3

2

2CN-1 (g) (h) 2CN-2

2CN-3 (i)

5

4

4

3

3

2

2

1

1

0 250

600

4

4

Molar absorptivity (M-1cm-1)

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

Page 16 of 18

350

450

550

650 250

350

450

550

650 250

350

450

550

650

0


Page 17 of 18

1250

2PA cross section (GM)

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


dipolar LE band for quadrupolar HE band for quadrupolar LE band for octupolar HE band for octupolar

1000 750

HE band 2CN-2

500

2CN-1

2CN-3

CNO2-2

LE band

CN-2

250

CN-3 (HE)

CNO2-1

LE band

CN-1 CNS-1 CN-3

0

16

18

20

22

24

26

28

30

32

34

36

Neff Figure 3 – 2PA cross section for the molecules with the same geometry as a function of the increase of πelectron effective number.



Page 18 of 18

Table 1 – Photophysical data for the molecules in chloroform. Molecules

abs max

 gfmax (M ―1cm

Nef ―1

)

(nm)

r

r

01

01eff

(D)

(D)

r 01

(D)

f

r eff 01

(D)

em max

Vol

(nm)

(Å3)

CN-1

420

1.63 x 104

16.4

5.4

1.33

9.5 ± 0.8

2.35

514

527.0

CN-2

448

3.64 x 104

20.7

6.5

1.43

11.8 ± 1.4

2.60

521

696.2

CN-3

441

3.37 x 104

24.2

5.6

1.14

12.5 ± 0.9

2.54

512

863.8

CNS

455

2.77 x 104

18.1

7.0

1.64

8.1 ± 0.3

1.90

554

579.2

CNO2-1

459

1.58 x 104

19.9

5.4

1.21

9.3 ± 1.7

2.08

569

567.5

CNO2-2

469

2.34 x 104

24.2

5.8

1.18

10.0 ± 0.7

2.03

554

777.6

2CN-1

498

1.50 x 104

21.7

5.4

1.16

10.1 ± 0.6

2.17

622

647.9

2CN-2

522

4.85 x 104

28.9

8.8

1.64

9.5 ± 0.7

1.77

621

936.0

2CN-3

503

3.34 x 104

34.6

5.5

0.94

10.6 ± 1.1

1.80

622

1219.3


Intramolecular Cooperative and Anti-Cooperative Effect on the Two

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