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Excited State and Two-Photon Absorption in Salicylidene Molecules: The Role of Zn(II) Planarization Marcelo G Vivas, José Carlos Germino, Cristina Aparecida Barboza, Pedro Antônio Muniz Vazquez, Leonardo De Boni, Teresa Dib Zambon Atvars, and Cleber R. Mendonca J. Phys. Chem. C, Just Accepted Manuscript • Publication Date (Web): 29 Jan 2016 Downloaded from http://pubs.acs.org on January 29, 2016

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The Journal of Physical Chemistry

Excited State and Two-Photon Absorption in Salicylidene Molecules: The Role of Zn(II) Planarization Marcelo G. Vivas,1,2* José Carlos Germino3, Cristina A. Barboza3, Pedro A. M. Vazquez3, Leonardo De Boni1, Teresa Atvars3 and Cleber R. Mendonça1 1

Instituto de Física de São Carlos, Universidade de São Paulo, Caixa Postal 369, 13560-970 São Carlos, SP, Brazil 2

Instituto de Ciência de Tecnologia, Universidade Federal de Alfenas, Cidade Universitária - BR 267 Km 533, 37715-400, Poços de Caldas, MG, Brazil 3

Chemistry Institute, State University of Campinas - UNICAMP, Campinas, SP, Brazil *Corresponding Authors: [email protected] and [email protected]

ABSTRACT

This paper report on the excited-state (ESA) and two-photon absorption (2PA) features of two novel salicylidene compounds: N,N’-bis(salicylidene)-1,2-phenylenediamine (salophen) and its Zn(II) coordination compound ([Zn(salophen)(OH2)]). The molecular structure of salophen is a tetradentated ligand with iminic and phenolic bonding sites, allowing the coordination of metal ions such as zinc(II) forming [Zn(salophen)(OH2)]. According to our data, the Zn(II) coordination complex modify the ESA and 2PA spectrum of the salophen ligand, increasing significantly its hyperpolarizability and improving its optical properties due to the increase of the planarity and rigidity of the ligand framework. In order to obtain more information about optical properties of these molecules, theoretical calculations were performed at DFT/TD-DFT level using aug-cc-pVDZ/CAM-B3LYP. Our results suggest that the molecular geometries of the ligand, corresponding to S0 and S1 states are quite similar. However, the coordination of the metal atom leads to an increment of the planarity and consequent increase of the electron delocalization of the ligand π framework, leading to an increment in the hyperpolarizability of the complex.

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I – INTRODUCTION

There are several studies

1-14

indicating that some coordination compounds containing

metal ions, such as Al(III), Zn(II), Li(I), Eu(III), Ir(III) and Ga(III), Yb(III), Os(II), with different ligands are suitable for applications in optoelectronics, nonlinear optical devices and sensors. 1521

For instance, Zn (II) complexes with several heterocyclic ligands, such as azomethanes and

benzothiazoles, have been used in several applications from biology to physics.

22-24

A series of

rich π-electrons molecules containing heteroatoms have been used as ligands. Among them are the Schiff bases, benzothiazoles, quinoxalines, phenanthrolines, thiophenes. The salicylidenes are particularly interesting since this type of ligand, the chelatogenic cycle (metal-oxygennitrogen chain) improves the intramolecular charge transfer (ICT) between the π-conjugated rings, contributing to increase the molecular hyperpolarizability of the compounds, potentiating their optical properties, allowing the development of novel optoelectronic devices. 25-28 In a previous study, we reported the synthesis, structural properties characterization and photophysical properties of some salicylidenes derivatives (N,N’-bis(salicylidene)-1,2phenylenediamine (salophen) coordinated to Zn(II) ion [Zn(salophen)(OH2)] (see Figure 1). 29 Nonlinear optical spectroscopies are powerful tools to investigate, at molecular level, different kinds of materials, since it allows identifying and obtaining quantitative information about the relationship between optical properties and molecular structure.

30-32

Two-photon

absorption has important advantages over conventional one photon absorption, leading to a series of applications, such as data storage, optical power limiting, among others.

5,33

These

applications have generated a demand for molecules with high two-photon absorption crosssections. 34 In this study, the effect of the coordination of an zinc(II) ion on the optical properties (hyperpolarizabilities, excited states and two-photon absorption – 2PA) of the salophen ligand was evaluated by white-light continuum pump-probe and open-aperture Z-scan techniques, using an amplified femtosecond laser system (160 fs) operating at low repetition rate (1 kHz). To obtain more information about the electronic structure of ligand and complex, calculations within the TD-DFT framework were carried out. This level of calculation has shown to be successful to obtain reliable theoretical predictions of 2PA states and cross-sections of organic chromophores. 35

The long-range corrected density functional CAM-B3LYP has been shown to be suitable to

study excitation energies and NLO properties, and it was chosen for the calculations. 36,37 2 ACS Paragon Plus Environment

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II – EXPERIMENTAL PROCEDURES A – FEMTOSECOND PUMP-PROBE MEASUREMENTS: Femtosecond time-resolved ESA spectra were recorded using 150-fs pulses (775 nm) from a Ti:sapphire chirped pulse amplified system operating at 1 kHz repetition rate (Clark 2001-MXR). The laser beam was divided in two using a beam splitter (90%-10%). The stronger beam was doubled (387.5 nm) using a BBO crystal and employed as the pump pulse. The weaker beam was used to generate the white-light continuum (WLC) probe, by using a sapphire plate. The time delay between pump and probe pulses was carefully varied by a computer controlled translation stage, providing a resolution of 187.5 fs. The intensity of the relative spectral components of WLC probe pulse, at each specific time, that characterize the time-resolved transient absorption (∆A), was monitored by means of a fast spectrometer. The chirp of WLC probe pulse was measured to be < 1 ps in the 400-700 nm spectral region. Pump and probe pulses energies were adjusted to be smaller than 1 µJ and 1nJ, respectively, and their polarizations relative angle was set to the magic angle (54.7o) to eliminate orientational components in the signal.

B – TIME RESOLVED EMISSION SPECTROSCOPY MEASUREMENTS

The time resolved emission spectra (TRES) were recorded using a time-correlated single photon counting (TCSPC) in an Edinburgh Analytical Instruments FL 900 spectrofluorimeter with a MCP-PMT detector (Hamamatsu R3809U-50). The excitation wavelength for [Zn(salophen)(OH2)] in DMSO dilute solution (10 µmol L-1, for this concentration we have 6.022 x 1018 molecules of [Zn(salophen)(OH2)] and 8.48 x 1024 of DMSO, and, therefore, the number of molecules of DMSO is about 106 times higher than the Zn(II) complex) was λexc = 405 nm (Edinburg pulsed diode model EPLED-405, with linewidth 0, which indicates that the absorption of the excited state is higher than the ground state one, characterizing a reverse saturable absorption (RSA) process. Hence, the ESA crosssections are higher than the corresponding of the ground state. 14,48 The time decay curve (symbol) displayed in Figure 3c was modeled using rate equations that describes the population dynamics induced by ultrashort laser pulses, according to: 49



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dnS0 ( t ) dt dnS1 ( t ) dt

= −nS0 ( t ) W01 +

nS1 ( t )

= + nS0 ( t )W01 − nS1 ( t ) W1n −

dnSn ( t ) dt

τR

+

nS1 ( t )

τR

= nS1 ( t ) W1n −

nS1 ( t )

−

τ NR

(1)

,

nS1 ( t )

τ NR

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+

nSn ( t )

τ Sn → S1

nSn ( t )

,

(2)

(3)

τ Sn → S1

where the transition rate is given by W01 = σ 01I pump ( hν pump ) and W1n = σ1n I probe ( hν probe ) . Here, σ 01 corresponds to the 1PA cross-section obtained though the linear absorption data ( Zn KG15 ) KG15 σ 01 = 3.0 × 10 −17 cm 2 and σ 01 ( = 8.2 × 10 −17 cm 2 at 390 nm)

and σ 1n is the cross-section between the

first and the nth excited state, which is associated with the amplitude of pump-probe signal. Here, this parameter was obtained taking in consideration the rhodamine B dissolved in ethanol as reference material. Ipump and Iprobe are the irradiance for the pump and probe pulses, h is the Planck constant, and ν is the photon frequency. τ R and τ NR are the radiative and non-radiative decay times, respectively. τ Sn → S1 is related with the internal conversion processes. In this

{

approach, ∆A ( t ) = N0 log(e) L nS0 ( t ) σ 01 + nS1 ( t ) σ1n

}

to describe the transient absorption

change, being N0 the concentration and L the optical path length. The solid line in Figure 3c correspond to the fit obtained using the model described by Eqs. (1) to (3), in which three characteristics decay times are observed. The faster component, of 4.6 ± 0.3 ps, can be assigned to internal conversion from higher energy singlet states, vibrational relaxation and solvent reorganization around the molecule ( τ Sn → S1 ). The slow decay, 40.7 ± 1.7 ps, is assigned to nonradiative relaxation ( τ NR ) from singlet excited to the ground state. The longer time, on the scale of nanoseconds, can be associated with the radiative relaxation from low-lying singlet excited state to the ground state ( τ R ). By measuring the emission decay time, with λexc = 335 nm and λem = 460 nm

29

, we determined τr = 4.54 ns. This value is typical of

Bases Schiff derivatives chromophores. 29,35 In the Figure 4 the ESA data for the [Zn(OH2)(salophen)] is given. Comparing to the salophen spectrum (that shows a band in 465 nm (Figure 4b)), an extra band is observed around 615 nm, also presenting a RSA effect (∆A > 0). This band is associated with the chelatogenic 6 ACS Paragon Plus Environment

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cycle formation (metal-oxygen-nitrogen) and has amplitude similar to the ESA ligand band observed in 465 nm. This band is not observed in the electronic absorption or in the steady-state emission spectra. 29 The dynamics for [Zn(salophen)(OH2)], also fitted by using Eqs. (1) to (3), change completely as shown in Figure 4c. For both bands (465 nm and 615 nm), a fast component of about 0.5 ps can be observed at the beginning of the curve, where ∆A increases in a slowly way compared with the salophen dynamics at the same time interval (Fig. 2c). In order to obtain more information about this process, the inset in the Figure 4c depicts a zoom of the dynamic curve. The observed profile can be related to the co-existing [Zn(salophen)(OH2)] compound and [Zn(salophen)(DMSO)] complexes in solution, where the H2O molecule attached to the zinc metal is changed by the DMSO molecule in solution. According to this hypothesis, the curve shown in Figure 4c could be explained as: (i) initially the electrons are promoted to the low-lying energy excited state within 0.5 ps, and (ii) subsequently they are re-excited through the probe pulse (white-light continuum) to a higher energy state associated with both the [Zn(salophen)(OH2)] and [Zn(salophen)(DMSO)] compounds (co-existing molecular species). This time scale involves the dynamics of both species and the increase in the ∆A is explained by the combination of the two different excited state absorptions, each one related to one molecular species. Both species have different ESA cross-section, which is plausible because each species will have a slightly different internal conversion rate from higher energy singlet states, vibrational relaxation and solvent reorganization around the excited molecules. All of these rate parameters depend on the interaction between the DMSO and the H2O on the molecular structure of the complex. 50 In other words, the interaction of the [Zn(salophen)(OH2)] compound and [Zn(salophen)(DMSO)] complex with the solvent molecules are different and, therefore, the excited state transition dipole moments are altered due to the charge redistribution caused by the polar solvent (DMSO). Consequently, the increase in ∆A with a characteristic time of 0.5 ps is caused by the different amount of co-existing molecular species. The initial concentration of 8 % and 92 % for the [Zn(salophen)(OH2)] and [Zn(salophen)(DMSO)] complex, respectively, is in agreement to the values obtained at the Zn(salophen) fluorescence decays as shown later (6% and 94% for aqueous and DMSO ligand substituent, respectively).

29

In the following, a

monotonic decay of about 36 ps dominates the global effect due to complete solvation of the 7 ACS Paragon Plus Environment


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both co-existing chromophores with the DMSO. For the second decay time, we obtained τ2 = 35.0 ± 2.2 ps and τ2 = 36.5 ± 2.8 ps, respectively, for the bands located at 465 nm and 615 nm, which are equivalent considering the experimental error. This decay is related to the nonradiative relaxation time from the excited singlet excited state to the electronic ground state for both species. Comparing these results with those obtained for salophen, it is noticeable the decrease of the nonradiative relaxation time of the Zn(II) coordination compound. This result can be, at least partially, explained by the introduction of the Zn (II) ion, which increases the number of nonradiative deactivation channels, contributing to the increase of nonradiative emission rate. This result is in good agreement with the decrease of the fluorescence quantum yield of the [Zn(salophen)(OH2)] as compared to the salophen, as well as with the pronounced decrease of the lifetime in the nanoscale time range. 29 In order to obtain more insights about the aqueous ligand substitution in the Zn(II) coordination complex by DMSO at diluted solution, time resolved emission spectra (TRES) of Zn(salophen) in DMSO solution (λexc = 405 nm; 10 µmol L-1; Figure 5) were carried out with time delays from 0.000 ns to 1.330 ns (according their fluorescence lifetimes 29). The TRES of Zn(salophen) exhibit a time-independent behavior at their two fluorescence bands, with a welldefined vibronic progression (λem = 495 nm (0-0) and 525 nm (0-1); Fig. 4b), with highest intensity at the t = 0.133 ns. Such results are in agreement with the fluorescence lifetimes and their components contributions to the fluorescence decay. Therefore, the highest time-resolved fluorescence intensity is attributed to the [Zn(salophen)DMSO] complex with shorter fluorescence lifetime (0.230 ± 0.040 ns) with greater contribution decay (94 %), in other hand, the [Zn(salophen)(OH2)] complexes exhibit the lower time-resolved fluorescence intensity and longer fluorescence lifetime (2.750 ± 0.010 ns), with low fluorescence decay contribution (6 %). These observations are in agreement with the femtosecond pump-probe dynamics and transient absorption. To shed more light on the relationship between molecular structure and optical properties of ligand and complex, the absorption spectrum for both molecules was calculated and their molecular structures corresponding to the ground (S0) and first excited (S1) state were optimized (Figure 6).


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29

As previously reported in Ref.

, the coordination of the metal atom leads to an

increment in the planarity of the ligand by with Cs symmetries for [Zn(salophen)(OH2)]. The structures of the Zn(II)-coordination compounds correspond to a bent conformation with an average deviation from planarity of ~33º, which decreases in the S1 structure to ~20º which could be related to the significant redshift observed in the complexes absorption and emission bands. A small shortening of the N···H distance by 13% in the optimized geometry of the excited state respective to the X-ray structure for salophen was obtained, however the excited proton transfer from the oxygen to the nitrogen atom is not observed for this ligand.

III.C –Two-Photon Absorption Spectra

Considering that metallosalophen derivatives have shown interesting NLO properties

51

,

two-photon absorption bands of ligand and complex were experimentally and theoretically characterized. Measurements were done using the wavelength tunable Z-scan technique with femtosecond pulses. Figure 7 shows the experimental 2PA spectra for both molecules, salophen (Fig. 7 a) and [Zn(salophen)(OH2)] (Fig. 7 b). According to the results given in Table 1, these chromophores present moderate 2PA cross-section values (from several tens to few hundreds of GM units) in the visible and infrared regions. In addition, both present a monotonic decreasing of the 2PA cross-sections with the excitation wavelength, suggesting a low 2PA probability for the lowest energy excited state. Another important result is that the [Zn(salophen)(OH2)] complex has 2PA cross-section approximately 60% higher than salophen along the whole nonlinear spectrum. This result can be ascribed at least to two important features: (i) the chetalogenic cycle may act as an ICT bridge between the two rings of the molecule and (ii) this same cycle increases the planarity of the πconjugated structure, as shown in Ref. moments

increases,

contributing

29

to

. In both cases, it is expected that the transition dipole the

higher

2PA

cross-section

found

to

the

[Zn(salophen)(OH2)]. In order to correlate the molecular structure changes involved in the metal coordination with the 2PA cross-section magnitude, theoretical calculations using linear and quadratic response functions within the TD-DFT framework were carried out. The density functional CAMB3LYP was chosen to calculate 2PA cross-sections, since it has shown a good performance 9 ACS Paragon Plus Environment


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to describe this parameter, compared to higher levels of calculation as CC2.

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37

For the response

calculations, the lowest fifteen states were calculated for each molecule. The effect of the solvent DMSO on the one-photon and two-photon properties were considered through the Polarizable Continuum Model (PCM) within its integral equation formalism variant (IEF-PCM). 52 Obtained results are summarized in Table 1. 2PA cross-sections were computed using linewidth values estimated through the fit of the nonlinear spectra (0.5 eV). Our results suggests that for the salophen the 1PA allowed transitions are also allowed by 2PA, which is not observed for the [Zn(salophen)(OH2)] complex. It is well known that in centrosymmetric molecules the one- and two-photon allowed transitions are antagonistic optical process.

53

From the TD-DFT calculations, the [Zn(salophen)(OH2)] complex belongs to the

symmetry point group Cs (centrosymmetric molecule), while salophen does not have a welldefined symmetry, allowing that transitions allowed by 1PA are also accessed by 2PA. As shown in Table 1, the 1PA and 2PA theoretical spectra are blue-shifted about 0.2 eV as compared to experimental spectra, for both molecules. This spectral shift is justified by recognizing that theoretical calculations using the polarizable continuum method - PCM to consider solvent effects - are performed under the Lorentz-Lorenz approximation and do not consider specific solute-solvent interactions.

52

In order to obtain more information about the

2PA results, the 2PA cross-section spectra was simulated assuming a Lorentzian linewidth of 0.5 eV (FWHM) for the fifteen calculated lowest energy transitions and performing a convolution of such functions. In Fig. 6, the scattered dots show the 2PA cross-section obtained for each specific transition. It is important to mention that to provide a better comparison with the experimental results, the theoretical spectra were red-shifted by 0.2 eV. As it can be seen, there is a good agreement between calculated (solid lines) and experimental (dots) non-linear spectral profile, as well as the 2PA cross-section magnitude for the salophen. However, for the [Zn(salophen)(OH2)] the difference between calculated and experimental data is larger, due most probably to the resonance enhancement effect present in experimental results when the excitation wavelength approaches the one-photon absorption region (< 600 nm). In Zn(salophen) molecule this effect is more pronounced because it presents a considerable red-shift as compared to the salophen molecule. Such effect is widely described in literature, inclusive as synthesis route to design of new chromophores with remarkable nonlinear optical properties. 54


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In order to obtain more information about the low-lying electronic transitions observed in the one and two-photon absorption spectra, the energy and density of the frontier orbitals are given in Figure 8. Although no metal to ligand charge transfer can be observed, the coordination of the salophen by the zinc(II) ion decreases the HOMO-LUMO gap, leading to a redshift of the ligand bands.The orbitals are mainly delocalized over the entire framework of both ligands and complexes, and these bands can be assigned as π→ π* transitions, with a small contribution to the orbitals from the Zn(II) and without participation of the aquo ligand. These findings can be attributed to the increased planarity of the complex, as previously mentioned in Ref. 29. IV – CONCLUSIONS

Here, we have investigated the Zn effect on the excited state and two-photon absorption properties of salicylidene molecules. We show that the Zn incorporation connecting two πconjugated arms to form a chelatogenic group increase considerably the 2PA cross-section and change completely the excited state dynamics in this class of molecules. For example, the 2PA cross-section is enhanced about 60% along the whole nonlinear spectrum as compared to the salophen molecule. Through the quantum chemical calculations, we show that this increase in 2PA cross-section is mainly associated with the increase of molecular planarity caused by the Zn(II). Regarding to the excited state dynamic, the [Zn(salophen)(OH2)] complex presents an extra band at 615 nm with ∆A > 0. This band was attributed the chelatogenic cycle formation and has amplitude similar to the ESA ligand band observed in 465 nm. By using the femtosecond white-light pump probe and TRES we observed that the Zn(salophen) co-exist in two molecular species, i. e., [Zn(salophen)(OH2)] and [Zn(salophen)(DMSO)] complex, where the H2O molecule attached to the zinc metal is changed by the DMSO molecule in solution. Our results revealed that the initial concentration for the [Zn(salophen)(OH2)] and [Zn(salophen)(DMSO)] species is around 7 % and 93 %, respectively.

ACKNOWLEDGEMENTS The authors acknowledge to Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESPgrant 2013/16245-2), Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Coordenação de 11 ACS Paragon Plus Environment


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Aperfeiçoamento de Pessoal de Nível Superior (CAPES), the National Institute of Organic Electronics (INEO) (MCT/CNPq/FAPESP), UNICAMP/FAEPEX for financial support and fellowships, GRID/UNESP, LCCA/USP and CENAPAD/SP for providing computational time.

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Figure Captions

Figure 1 – Molecular structure of salophen free ligand and its zinc(II) coordination compound. Figure 2 –Ground-state absorption (squares and diamonds – left axis) and fluorescence spectra of KG-15 (squares) and Zn(KG-15) (diamonds). Figure 3 – Excited state dynamics for the salophen molecule. (a) ESA colormap representing the time- and wavelength-resolved dynamic of transient absorption spectrum. (b) ESA spectra for different times (0 ps, 12 ps and 50 ps). (c) Decay curve for probe pulse at 465 nm. Figure 4 – Excited state dynamics for the [Zn(salophen)(OH2)]. (a) ESA colormap representing the time- and wavelength-resolved dynamics of transient absorption spectrum. (b) ESA spectra for different times (0 ps, 8 ps and 23 ps). (c) Decay curves for probe pulse tuning at 465 and 615 nm (this ESA curve was plotted as ∆A/2 to better visualization of results). Figure 5 – Time resolved emission spectra (TRES) (a.) and normalized TRES (b.) of [Zn(salophen)(OH2)] in DMSO solution (λexc = 405 nm; delays: 0 to 1.330 ns; concentration: 10 µmol L-1). Figure 6 – Molecular structures and selected geometry parameters for the S0 (black) and S1 (red) excited states of salophen and its zinc(II) complex obtained at CAMB3LYP/aug-cc-pVDZ level. Figure 7 – 2PA spectrum for (a) salophen and (b) [Zn(salophen)(OH2)] molecules. The dots represent the 2PA cross-section spectra and the solid lines along them the theoretical fitting obtained at CAMB3LYP/augcc-pVDZ level. The theoretical spectra were red-shifted at 0.2 eV to better comparison with the experimental results. Figure 8 – Frontier Molecular Orbitals for the ligand and complex obtained at CAM-B3LYP/aug-cc-pVDZ level.


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Figure 1



3.5

3

2.5

2

1.2

KG-15 Zn(KG-15)

4

-1

-1

3 4.5 4

0.9

2 0.6

1 0.3

0 250

350

450

550

0.0

Normalized fluorescence

Energy (eV)

Molar absorptivity (10 M cm )

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

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650

Wavelength (nm)

Figure 2


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Figure 3



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

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Figure 4


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1.2

8000 0.000 ns 0.133 ns 0.266 ns 0.399 ns 0.532 ns 0.665 ns 0.798 ns 0.931 ns 1.064 ns 1.197 ns 1.330 ns

6000

4000

2000

0

Normalized intensity

Counts (arb. units)

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


a 450

500

550

600

650

700

750

0.000 ns 0.133 ns 0.266 ns 0.399 ns 0.532 ns 0.665 ns 0.798 ns 0.931 ns 1.064 ns 1.197 ns 1.330 ns

0.9

0.6

0.3

0.0

Wavelength (nm)

b 450

500

550

600

650

700

750

Wavelength (nm)

Figure5



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Figure 6


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Transition energy (eV) 5.5 200

5

4.5

4

(a)

Transition energy (eV)

3.5

3

2PA cross-section (GM)

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


salophen CAMB3LYP/aug-cc-pVDZ

150

100

50

0 450

550

650

750

850

5.5 400

5

4.5

4

(b)

3.5

3

Zn(salophen)(OH2) CAMB3LYP/aug-cc-pVDZ

300

200

100

950

Laser wavelength (nm)

0 450

550

650

750

850

950

Laser wavelength (nm)

Figure 7



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Figure 8


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Table 1 – Experimental data and main theoretical results of the CAMB3LYP/aug-cc-pVDZ calculations using the linear and quadratic response functions. Transition energies (E) in eV, oscillator strength (f), two-photon transition probability (P) in a.u., and 2PA cross-section (σ) in GM. The 2PA cross-sections were computed adopting linewidth values estimated through the fit of the nonlinear spectra (~ 0.5 eV).

−theo E 1 P A − exp E01PA 0i i

Salophen

[Zn(salophen)(OH2)]

f 0theo i

PA− E02iPA−theo E 02i exp

σ 0( i

theo )

P

( exp ) σ 0i

-

-

-

3.39

-

0.211×103

0.36

-

3.74

3.40

0.40

3.75

3.55

0.856×104

17.8

22.65

4.12

3.76

0.63

4.98

4.77

0.318×105

116.5

93.90

3.36

2.92

0.26

3.05

-

0.135×105

21.06

-

-

-

-

3.75

3.10

0.249×105

57.40

18.26

3.60

4.13

0.64

3.87

3.65

0.396×105

96.8

40.45

-

-

-

4.45

0.211×105

59.49

5

67.65

4.18 4.57 -

-

-

-

0.202×10

304.9 5



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TOC


Excited-State and Two-Photon Absorption in ... - ACS Publications

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