Solvent Effect on the Third-Order Nonlinear Optical Properties of Î±

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Solvent Effect on the Third-Order Nonlinear Optical Properties of # and #-Tertbutyl Phenoxy Substituted Tin(IV) Chloride Phthalocyanines Marcel Louzada, Jonathan Britton, Tebello A Nyokong, and Samson Khene J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.7b07349 • Publication Date (Web): 06 Sep 2017 Downloaded from http://pubs.acs.org on September 11, 2017

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The Journal of Physical Chemistry

Solvent Effect on the Third-order Nonlinear Optical Properties of α and β-tertbutyl Phenoxy Substituted Tin(IV) Chloride Phthalocyanines Marcel Louzada, Jonathan Britton, Tebello Nyokong and Samson Khene*

Department of Chemistry, Rhodes University, PO Box 94, Grahamstown 6140, South Africa Contact details *[email protected]

Abstract This paper investigates the third-order nonlinear optical properties of 4α-(4-tertbutylphenoxy) phthalocyaninato dichlorotin(IV) (α-SnOtBpPc) and 4β-(4-tertbutylphenoxy) phthalocyaninato dichlorotin(IV) (β-SnOtBpPc) in different organic solvents. The third-order susceptibilities of α-SnOtBpPc and β-SnOtBpPc are reported in different solvents, using Z-scan techniques with 10 ns laser pulses at 532 nm. Their nonlinear absorption coefficient and absorption cross sections were also determined.

The

molecular

imaginary

component

of

the

second-order

hyperpolarizability of α-SnOtBpPc and β-SnOtBpPc were found to be 2.60x1031

and 2.94x10-31 esu (tetrahydrofuran), 2.12x10-31 and 2.54x10-31 esu (chloroform),

3.06x10-31 and 2.54x10-31 esu (dichloromethane) and 1.27x10-31 and 1.50x10-31 esu (toluene) respectively. This study found that substitution at the alpha position has an effect of lowering two-photon (2PA) cross section value for α-SnOtBpPc compared to β-SnOtBpPc, with values of 64.30 GM and 456.65 GM respectively. The large 2PA cross-section observed in β-SnOtBpPc is attributed to the decreased energy difference between the virtual state and the LUMO.

Key words: Tin(IV)phthalocyanine, solvent effect, Z-scan technique and density functional theory (DFT). 1 ACS Paragon Plus Environment


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1. Introduction A range of important modern devices makes use of nonlinear optical (NLO) materials. Optical computing, optical limiting and optical communication are some of the modern day applications [1-4]. Optimizing the design of third order nonlinear optical materials for a given application depends largely on the understanding of the physical mechanisms responsible for the nonlinear response. Strong nonlinearities in organic molecules are known to usually arise from highly delocalized ̟-electron systems [5, 6]. Phthalocyanines (Pcs) are known to possess highly delocalised 18 ̟electron systems and can be easily processed into thin films. This property makes Pcs ideal for use as NLO materials. Tunability of a Pc’s 18 ̟-electron system, by introducing peripheral and non-peripheral substituents, offers some controlled way for fundamental NLO studies [4, 7]. Tuning a Pc’s 18 ̟-electron system can alter the electronic structure of the macrocycle hence can lead to improvement of the thirdorder NLO response. The 2D dimensional structures of Pcs offers the possibility of investigating the role of dimensionality on the NLO response and offer more variables for optimization [8, 9]. NLO response is known to better correlate with 2D structures than for 1D molecules, hence Pcs are ideal candidate for studying the effect of solvent polarity on nonlinear response. Apart from one literature report [10] this work is the first systematic study of the effect of solvent polarity on tetra substituted 4α-(4-tert-butylphenoxy) phthalocyaninato dichlorotin(IV) (α-SnOtBpPc) and 4β-(4-tert-butylphenoxy) phthalocyaninato dichlorotin(IV) (β-SnOtBpPc) using Z-scan technique. The molecular second-order hyperpolarizability Im(γ) values are determined in chloroform, dichloromethane, tetrahydrofuran and toluene. The twophoton (2PA) cross sections are also determined using the five energy level model.

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2. Experimental 2.1. Materials N, N-dimethylformamide (DMF), dichloromethane (DCM), hexane, chloroform, toluene, tetrahydrofuran (THF), methanol, ethanol, 1-octanol, 1-pentanol and silica gel

were

purchased

from

Merck.

4-t-butylphenol,

Phthalamide,1,8

diazabicyclo[5.4.0]undec-7-ene (DBU), Tin Chloride (SnCl2), Thionol Chloride and 1thiol Pentane were purchased from Sigma Aldrich. Chloroform, DCM, THF and Toluene were dried using molecular sieves (0.4 nm, rods). The synthesis of 4α-(4tert-butylphenoxy) phthalocyaninato dichlorotin(IV) (α-SnOtBpPc) and 4β-(4-tertbutylphenoxy) phthalocyaninato dichlorotin(IV) (β-SnOtBpPc), shown in Scheme 1 and 2, have been reported before [12] (see supplementary information for their detailed synthesis and characterisation). 2.2. Equipment Ground state absorption spectra, magnetic circular dichroism (MCD) spectra, excitation spectra, emission spectra, fluorescence lifetimes, rotational lifetimes, mass spectral data and Z-scan measurements were recorded on instruments mentioned in this reference [11]. Gaussian 09-software package [12] was used to perform density functional theory (DFT) and time dependent density functional theory (TDDFT) calculations as indicated here [11]. 3. Results and discussion 3.1. Synthesis and Characterisation 4α-(4-tert-butylphenoxy) phthalocyaninato dichlorotin(IV) (α-SnOtBpPc) and 4β-(4tert-butylphenoxy) phthalocyaninato dichlorotin(IV) (β-SnOtBpPc) were synthesized as shown in Scheme 1 and 2 and following literature method [13]. The 4-tertbutylphenoxy substituents were chosen because of their good solubility in most organic solvents. The isolated products of α-SnOtBpPc and β-SnOtBpPc both possessed strong IR bands at 1245, 2928 and 3108 cm-1. The band at 1245 cm-1 correspond to an unsymmetrical vibrations of the ether bond that was expected to be present due to the substituent, while the bands at 2928 and 3108 cm-1were due to the 3 ACS Paragon Plus Environment


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C-H stretching of tert-butyl group. The phenoxy group (Ph-O) IR stretch was observed at 1245 cm-1. Elemental results of the complexes confirm the synthesis and purity of α-SnOtBpPc and β-SnOtBpPc. 3.2. Electronic absorption and MCD spectroscopy Figure 1 (a) and (b) shows a typical UV-visible(bottom) absorption and MCD (top) spectra of metallated α-SnOtBpPc and β-SnOtBpPc respectively in chloroform. The presence of an intense Faraday A1 terms, in the MCD spectra, coinciding with the main electronic Q (0, 0) band (at ca. 740 and 705 nm region) is evidence of the complete metalation of α-SnOtBpPc and β-SnOtBpPc respectively [14, 15]. The MCD spectra of α-SnOtBpPc and β-SnOtBpPc showed a distinct Faraday A1 term for the Q band as expected for a phthalocyanine with a D4h symmetry [15, 16]. The presence of Faraday A1 terms indicates that the lowest unoccupied molecular orbital (LUMO) and LUMO+1 (eg-orbitals) are degenerate. The effect of substitution at the alpha position shift the Q band by 27 nm to the red as expected. A relatively weaker B band is observed in the 350 nm region, which is typical of most phthalocyanine complexes. The TD-DFT calculated transition results for both α-SnOtBpPc and β-SnOtBpPc, as listed in Table 1, showed no transition between the Q and B bands and showed good prediction of the two degenerate transitions as expected. The transitions originate from to the → − and → − (as shown in Table 1) in Michl’s four frontier orbitals, shown in Figure 2. TD-DFT calculations correlates well with experimental MCD spectra, as evident by the Faraday A1 term. 3.3. Fluorescence lifetimes The photophysical data for α-SnOtBpPc and β-SnOtBpPc was carried out with time correlated single photon counting (TCSPC) spectroscopy, enabling the study of their fluorescence

lifetimes

(τ)

in

tetrahydrofuran, see Table 2.

chloroform,

toluene,

dichloromethane,

and

All measurements were taken at very low

absorbances, around 0.05, to reduce intermolecular interactions. Figure 3 shows the absorption, excitation and emission spectra of β-SnOtBpPc in chloroform, to serve as


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an example. The excitation spectra of α-SnOtBpPc and β-SnOtBpPc were identical to the absorption spectra, suggesting that the molecule absorbing is the same one emitting. A typical time resolved mono-exponential fluorescence decay curve obtained in chloroform for β-SnOtBpPc, see Figure 4. α-SnOtBpPc showed an increasing fluorescence lifetime in different solvent in the following order: dichloromethane (3.05 ns) < tetrahydrofuran (4.13 ns) < chloroform (4.84 ns) < toluene (5.13 ns). β-SnOtBpPc showed an increasing fluorescence life times in different solvent in the following order: toluene (3.43 ns) < tetrahydrofuran (4.57 ns) < chloroform (4.52 ns) < dichloromethane (5.55 ns). The polarity index of toluene, chloroform, dichloromethane and tetrahydrofuran are (2.4), (2.7), (3.1) and (4.0) respectively. The fluorescence lifetimes were found to be affected by solvent polarity; however, they were all within typical fluorescence lifetimes of phthalocyanine complexes [16]. The above results suggest that toluene and dichloromethane solvents have a different interaction with α-SnOtBpPc and βSnOtBpPc,

since

α-SnOtBpPc

showed

the

shortest

fluoresce

lifetime

in

dichloromethane and longest lifetime in toluene. β-SnOtBpPc shows the opposite fluorescence lifetime trend to α-SnOtBpPc in dichloromethane and toluene. Table 2 shows rotational correlation times (φ), determined by TCSPC, which were used to calculate molecular volume (Vm) occupied by α-SnOtBpPc and β-SnOtBpPc in different solvents. Equation 1 below was used to calculate Vm [11]. φ=

(1)

were k is the Boltzman constant, η the viscosity at 293 K (0.65 (toluene), 0.54 (chloroform), 0.53 (THF) and 0.43 mm2/s (DCM)), Vm the molecular volume and T the absolute temperature (293 K). The Vm values for β-SnOtBpPc were determined to be 5.99 x 10-29 (chloroform), 9.71 x 10-29 (DCM), 6.59 x 10-29 (THF), and 5.87 x 10-29 m3 (toluene) and α-SnOtBpPc: 7.64 x 10-28 (Chloroform), 9.56 x 10-29 (DCM), 1.14 x 10-27 (THF) and 1.66 x 10-27 m3 (toluene) (see Table 2). On average β-SnOtBpPc Vm values were calculated to be lower (order of 10-29 m3) in all solvents compared to α-SnOtBpPc which gave varying Vm values 5 ACS Paragon Plus Environment


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(between the order of 10-29 and 10-27 m3) in different solvents. Large Vm values (corresponding to long rotational correlation time) suggest that a greater number of solvent molecules interact with the solute and hence does not allow free movement of the solute in solution [11]. α-SnOtBpPc showed significantly longer rotational correlation times in toluene, THF and chloroform, compared to β-SnOtBpPc. The differences in Vm values, observed for β-SnOtBpPc and α-SnOtBpPc, suggests that the interaction of α-SnOtBpPc with toluene, THF and chloroform is significantly different compared to β-SnOtBpPc. However, in DCM, β-SnOtBpPc and α-SnOtBpPc show similar Vm values (hence similar physical interaction), but their fluorescence lifetimes are significantly different (see Table 2). The above observation is different for toluene, whereby β-SnOtBpPc and α-SnOtBpPc show different Vm values (with α-SnOtBpPc having the longest rotational correlation time) corresponding to significantly different fluorescence lifetimes. The above observation suggest that toluene and DCM have significantly different interaction with β-SnOtBpPc and αSnOtBpPc as observed from their opposite fluorescence lifetime trends discussed above. The above suggest that the solvent solute interaction involves physical interaction (as observed in differences in rotational correlation times) which involves the number of solvent interacting with the solute (viscosity) and electrostatic interaction (as observed in differences in fluorescence lifetimes) known to involve solvent dipole orientation.

3.4.

Determination

of

the

imaginary

component

of

the

second-order

hyperpolarizability () using Z-scan technique Figure 5 shows the Z-scan transmittance plot of α-SnOtBpPc (A) and β-SnOtBpPc (B) in toluene, similar plots were obtained for α-SnOtBpPc and β-SnOtBpPc in different solvents (with concentrations of 6.53 x 10-6 M and 6.77 x 10-6 M for α-SnOtBpPc and β-SnOtBpPc respectively). Figure 5 (bottom) shows the plot of q0 (zs) and its fitting, q0 is a parameter characterizing the strength of the nonlinearity as described in the supplementary information. The Z-scan data was obtained with laser peak power of 10 µJ for determining the intensity dependent non-linear absorption coefficient ( ). 6 ACS Paragon Plus Environment

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The experimental data is represented as scattered points and the theoretical fit as a solid line. was extracted from the Z-scan data by using Tsigarida’s method [17],

see supplementary information. was observed to increase with increasing laser

intensity or laser peak power, suggesting that the z-scan data was dependent on the laser intensity (see Figure S1). The values are shown in Table 3. Using Equation

(9), values were used to calculate the imaginary component of the second-order

hyperpolarizability

()

and

imaginary

component

of

the

third-order

susceptibility ( ) values in chloroform, dichloromethane, tetrahydrofuran and

toluene, see Table 4. Figure 6 shows the values for α-SnOtBpPc and β-SnOtBpPc in increasing solvent polarity. All the results obtained in Figure 6A and 6B were repeated three times (n = 3) in each solvent in order to determine the error bars for each data point.

The values determined for both α-SnOtBpPc and β-SnOtBpPc were found to

increase with increasing solvent polarity. The magnitude of values of βSnOtBpPc were found to be generally higher (by a factor of 10) compared to αSnOtBpPc in all four solvents. General enhancement of polarizabilities and hyperpolarizabilities have been found to be due to electrostatic interaction between solute and solvent [18]. Using the degenerate four wave mixing (DFWM) method, Zielinska et al. [10] found that the solvent polarity as well as the central metal ion

played a crucial role in determining the values of for copper, cobalt, zinc and magnesium phthalocyanines in ethanol and dimethyl sulfoxide. values were found to be higher for samples dissolved in polar aprotic solvent than in polar protic

solvent. Generally the values are expected to be lower when determined with a femtosecond laser compared to nanosecond laser (used in this work) [19]. The higher values for β-SnOtBpPc suggest that the electronic structure of αSnOtBpPc is not easily polarisable compared to β-SnOtBpPc. The differences in magnitude of the

between the α-SnOtBpPc and β-SnOtBpPc can be

attributed to the destabilisation of the highest occupied molecular orbital (HOMO) of α-SnOtBpPc, by the electron withdrawing phenoxy substituents. Substitution at the alpha position is known to have a substantial effect on the molecular orbitals of



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the Pc, because of the high molecular coefficient at the alpha position compared to the beta position (see Figure 2). Substitution at the beta position has less or negligible effect on the electron distribution for β-SnOtBpPc, as the beta position is further away from the molecular orbitals of the Pc macrocycle. The above suggest that phthalocyanine substituted at the beta position with phenoxy substituents will generally

have

higher

values

compared

to

alpha

substituted

phthalocyanines. However, the observed increase in values with increasing solvent polarity for both α-SnOtBpPc and β-SnOtBpPc suggest a similar solventphthalocyanine interaction for both complexes. Hence the observed differences in magnitude of

can be attributed to be due to differences in electron

distribution between the two systems. The highest values of 6.41 and 20.71 x10-12 esu were observed in the most polar solvent (THF) for both α-SnOtBpPc and β-

SnOtBpPc respectively. The values obtained are higher than value of Sn(IV) phthalocyanine substituted with fluorines (5.58 x 10-12 esu in THF) reported in

literature [20]. The high values are attributed to the solvent dielectric

constant and solvent-Pc electronic interaction, whilst the values in the least

polar solvents can be affected by Pauli repulsion and dispersion solute-solvent interactions [18]. It has been theoretically shown that Pauli repulsion can give rise to important effects for non-polar solvents and that it does not depend on the dielectric constant [18]. However, Tomasi et al. [21] have shown that electrostatic interaction between solute and solvent is the most important effect on the nonlinear response of solute.

2.4.2. Calculation of ground state cross section The five level system in Scheme 3 can be treated with 5-level model rate Equations (2)-(6) [22]: "#

! ( ,( = − + + − 2"ℏ&# )*+ )+ ℏ&


(2)

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"#

( ( ! * ( ( ( = − + − − 2"ℏ&# )*+ )* ℏ& )*

(3)

,( - ,( ,! ( ,( = − + − ℏ& )- )* )+

(4)

,! - ,( ,! = − ℏ& )-

(5)

! * ( ! = − ℏ& )*

(6)

where +* , * , and - are the cross sections describing ground state to * state,

* to some state . , and /* to some triplet state /. respectively, ℏ is Planck’s

constant, ω is the frequency of light, the Ni’s represents the populations in different "#

states; ! is the two photon absorption (2PA) cross-section, the τi’s are the rate constants of the respective states. The intensity transmitted through the sample is represented as I. The intensity transmitted through the sample (I) is given by Equations 7 and 8.

0 0 0 "# = = +* * + * + - + 12 3 12 12 !

(7)

with

= ++ 4

ω+

ω "z#

7 89: 4−

7 89: 4−

τ;

2< 7 & "3#

(8)

where nr is the solution refractive index (nr = 1.497 for toluene), c is the speed of light in vacuum, I00 is the peak intensity at the focus of Guassian beam; τp is the input pulse width; =0 is beam waist at focus, z0 is Rayleigh range and r is the radius of the aperture. dI/dz in Equation (6) describes the change of intensity with propagation 9 ACS Paragon Plus Environment


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of laser light through the sample with z as the position of the sample in the beam profile. Since the lifetimes of Sn, and Tn can be very short [23, 24], these level can be neglected and only the time variation of populations N0, N1 and N2 corresponding to S0, S1 and T1 energy level has been accounted for in Equations (1)-(5). The rate equations (Equations (1)-(5)) were numerically solved following the methods of Zhang et al [25]. The experimental data (scattered point) and the theoretical fit (solids line) for α SnOtBpPc and β-SnOtBpPc in toluene is shown in Figure 7. The absorption crosssection for the ground state was calculated using Equation (9).

+* =

>

0

(9)

where α is the linear absorption and N0 is the number of molecules per cm3. Table 5 shows the two photon absorption cross section (@ABC [GM]), singlet state

absorption cross section (@D A ), and triplet state absorption cross section ( @E A ) determined for α-SnOtBpPc and β-SnOtBpPc in toluene. The above cross

sections were determined by fitting experimental data with the five-level model equations. Figure 7 (A) and (B), showed a five-level model nonlinear fit to Z-scan data of α-SnOtBpPc and β-SnOtBpPc respectively. The fit and experimental data show a decrease in transmittance at the focal position (z = 0 cm), signifying a reverse saturable absorption (RSA) behaviour. RSA behaviour is only observed when the excited singlet state absorption cross-section (@D ) is greater than the ground state absorption cross-section (@F ). The ground state absorption cross section (see Table 6) of α-SnOtBpPc and βSnOtBpPc are determined to be 4.28x10-18 and 4.24x10-18 cm2 respectively. The above results show that β-SnOtBpPc and α-SnOtBpPc have similar ground state absorption cross section. However, two photon absorption (2PA) cross section (@ABC ) of αSnOtBpPc and β-SnOtBpPc were determined to be 64.30 and 456.65 GM respectively. The two-photon absorption cross section values are of the order expected for a nonsandwich Pc complex, which have values typically twice the size of those reported 10 ACS Paragon Plus Environment

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here [24]. The differences in the 2PA is attributed to the differences in substituents position. The observed differences in the @ABC correlates with the shifting of the Q band, with

the most red shifted α-SnOtBpPc having the smallest GH . It is understood that the 2PA cross section values determined for α-SnOtBpPc and β-SnOtBpPc represents an average of 2PA cross sections of a mixture of isomers (Cs,D2h, C4h and C2v), which may not necessarily have the same 2PA cross section. However, the differences in the measured @ABC are attributed to the differences in the HOMO-LUMO gap of αSnOtBpPc and β-SnOtBpPc, see Figure 8. According to the essential state model, the 2PA cross section is approximated by Equation (10) [26].

,GH ≈ J

N N KLM KMO

N

PQRLM /TUVW*X Y

(10)

The three “essential” states wave functions in this model are the ground state (|[\ ),

the intermediate sate (|]\ ) and the final excited-state (|^\). The |[\ and |^\ wave

functions are gerade, whereas |]\ is ungerade. However, in phthalocyanines the |[\ and |^\ wave functions are ungerade, whereas |]\ is gerade [27]. It is known that in

the presence of one-photon with the optical frequency _ (532 nm in this work, which

is out of resonance with allowed electric dipole transitions), the superposition of |[\

and |]\ creates a non-stationary state or virtual state which exist only for about 5 fs [26]. This virtual state represent an induced polarisation, which corresponds to an energy difference between the intermediate and virtual state energy, Δ = abc /ℎ_ − 1.

The transient presence of |]\ (with gerade parity) in the virtual state makes it

possible to induce an electric-dipole transition to |[\ (with ungerade parity). In

phthalocyanines the virtual state is expected to lie above the LUMO energy, therefore Δ in this work will represent the energy difference between LUMO and the virtual state. The energy difference between LUMO and the virtual state for αSnOtBpPc and β-SnOtBpPc were calculated to be 0.272 and 0.245 eV respectively, see Table 7. The above results suggest that the smaller the Δ value the greater the 2PA cross section. The above observation suggest that substitution at the alpha position



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has an effect of substantially lowering two-photon cross section value in α-SnOtBpPc compared to β-SnOtBpPc, which explains the measured low value SnOtBpPc = 1.27x10-31 esu and β-SnOtBpPc

(α-

= 1.50x10-31 esu) obtained for this

complex in Toluene. It is well known that the triplet excited state cross-section contributes more to the nonlinear absorption in phthalocyanines [28] (when nanosecond laser is used). The resulting population dynamics plays a greater role in producing the observed nonlinear absorption. In this study, this effect is observed from the plot of versus laser peak power in toluene (see supplementary

information). As the laser peak power increased the value increased as the

population in the ground state diminished, suggesting that the dominating factor is not the 2PA but the triplet state in the observed nonlinear absorption. A more accurate analysis in explaining the values, would be a comparison of

the ratio of the ground state absorption coefficient (@fg ) with the total excited state cross-section (@h ). The ratio (@h /@fg # of the cross-sections for α-SnOtBpPc and β-

SnOtBpPc were calculated to be 5.14 and 9.62 respectively (see Table 6). The high cross section ratio for both complexes implies that the excited state cross-section (@h )

is greater than the ground state cross section ( @fg ), which will result in the observed

reverses saturable absorption (RSA) as discussed above (see Figure 7). 4. Conclusion The synthesis, photophysical and nonlinear properties of α-SnOtBpPc compared to β-SnOtBpPc in a range of solvents were carried out. It was found that β-SnOtBpPc has far higher values, despite having a much lower singlet state absorption cross section. This was attributed to β-SnOtBpPc having higher 2PA and triplet state cross-sections. The work demonstrated that the larger 2PA cross-section seen in the beta type Pc is due to decreased energy difference between the virtual state and the LUMO. This study found that phthalocyanine substituted at the beta position with

phenoxy substituents will generally have higher values compared to alpha substituted phthalocyanines. The increase in values with increasing solvent

polarity for both α-SnOtBpPc and β-SnOtBpPc suggested a similar solvent-


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phthalocyanine interaction for both complexes. Substitution at the alpha position was found to have an effect of lowering two-photon (2PA) cross section value for αSnOtBpPc compared to β-SnOtBpPc, with values of 64.30 GM and 456.65 GM

respectively. The i values obtained for α-SnOtBpPc and β-SnOtBpPc in tetrahydrofuran were found to be higher compared to other Sn(IV) phthalocyanine complexes reported in literature. Supporting Information Available The supporting information contains detailed synthesis and characterisation of αSnOtBpPc and β-SnOtBpPc, instruments and equations used to analyse z-scan data and nonlinear absorption coefficient versus laser peak power plot. 5. Acknowledgments This work was supported by the Department of Science and Technology (DST)/Nanotechnology (NIC) and National Research Foundation (NRF) of South Africa through DST/NRF South African Research Chairs Initiative for Professor of Medicinal Chemistry and Nanotechnology (UID 62620), National Research Foundation (NRF) Thuthuka (UID = 84188) and Rhodes University.



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6. References 1. He, T.; Zhang, B.; Shen, J.; Zang M.; Chen, T.; Hu, Y.; Hou Y. High-efficiency THz modulator based on phthalocyanine-compound organic films, Applied Physics Letters 2015, 106, 0533031-0533031. 2. Nagamura, T.; Naito, A.;

Yoshida, I.; Chen, Y.; Hanack, M. All-Optical

Reflectance Control Based on Photoinduced Complex Refractive Index Changes in Guided Mode Thin Films Containing Indium or Gallium Phthalocyanines, Journal of Nonlinear Optical Physics & Materials. 2002, 11.03, 205-218. 3. Yao, C.; Zhang, Y.; Sun, W.; Yu, C.; Li, J.; Yuan, P. The lifetime of the triplet excited state and modulation characteristics of all-optical switching in phenoxy-phthalocyanines liquid, Opt Express. 2013, 21, 2212-22129. 4. De la Torre, G.; Vazquez, P.; Agullo –Lopez, F.; Torres, T. Role of Structural Factors in the Nonlinear Optical Properties of Phthalocyanines and Related Compounds, Chem Rev. 2004, 104, 3723-3750. 5. Kadish, K.M.; Smith, K.M.; Guilard, R. eds. Porphyrin and Phthalocyanine Handbook: Academic Press: Boston, MA, 2003; Vols. 11-20 6. Long, N.J. Organometallic Compounds for Nonlinear Optics, Angew Chemie Int Ed. 1995, 34, 21-38. 7. Hanack, M.; Heckman, H.; Polley, R. In Methods in Organic Chemistry (Houben-Weyl); Schuman, E., Ed.; Georg ThiemVerlag: Stuttgart, 1998; Vol. E 9d, pp 71-833. 8. Dini, D.; Calvete, M.J.F.; Hanack M.; Meneghetti, M.; Indium Phthalocyanines with Different Axial Ligands: A Study of the Influence of the Structure on the 14 ACS Paragon Plus Environment

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Mack, J.; Louzada, M.; Khene, S.; Britton, J.;

Nyokong, T. Improved nonlinear optical behaviour of indium ball type phthalocyanine linked to glutathione capped nanoparticles, Dyes and Pigments 2017, 140, 417–430. 10. Derkowska-Zielinska, B. The effect of solvent polarity on second-order hyperpolarizability of selected phthalocyanines complexes, Molecular Crystals and Liquid Crystals 2016, 639, 71-77. 11. Ngubeni, G. N.; Britton, J.; Mack, J.; New, E.; Hancox, I.; Walker, M.; Nyokong, T.; Jones, T. S.; Khene, S. Spectroscopic and nonlinear optical properties

of

the

four

positional

isomers

of

4α-(4-tert-

butylphenoxy)phthalocyanine, J. Mater. Chem. C 2015, 3, 10705—10714. 12. Frisch, M.J.; Trucks, G.W.; Schlegel, H.B.; Scuseria, G.E.; Robb, M.A.; Cheeseman, J.R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A., et al. Gaussian 09, Revision D.01, Gaussian, Inc., Wallingford CT 2009. 13. Idowu, M.; Nyokong, T. Synthesis, photophysics and photochemistry of tin(IV) phthalocyanine derivatives, Journal of Photochemistry and Photobiology A: Chemistry 2008, 199, 282–290. 14. Mack, J.; Kobayashi, N. Low Symmetry Phthalocyanines and Their Analogues, Chem. Rev. 2011, 111, 281-321. 15. Mack, J.; Stillman, M.J.; Kobayashi, N. J. Coordination Chemistry Reviews 2007, 251, 429-453. 16. Nomboma,

N.;

Chidawanyika,

W.;

Nyokong,

T.

Spectroscopic

and

physicochemical behavior of magnesium phthalocyanine derivatives monosubstituted with a carboxylic acid group, J. Mol. Struct. 2012, 1012, 31-36. 17. Tsigaridas, G.; Polyzos, I.; Persephonis, P.; Giannetas, V. A novel approach for analyzing open Z-scan experiments, Opt. Commun. 2006, 266, 284-289. 18. Mennucci, B.; Amovilli, C.; Tomasi, J. On the effect of Pauli repulsion and dispersion on static molecular polarizabilities and hyperpolarizabilities in solution, Chemical Physics Letters 1998, 286, 221-225. 15 ACS Paragon Plus Environment


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19. Raavi, S. S. K.; Venugopal Rao, S.; Giribabu, L.; & Narayana Rao, D. (2008). Nonlinear optical properties of alkyl phthalocyanines in the femtosecond, nanosecond, and cw excitation regimes. Proceedings of SPIE 2008 6875, 68751D. 20. Slodek, A.; Wöhrle, D.; Doyle, J.J.; Blau, W. Metal Complexes of Phthalocyanines in Polymers as Suitable Materials for Optical Limiting. Macromol Symp. 2006, 235, 9-18. 21. Tomasi, J.; Persico, M. Molecular Interactions in Solution: An Overview of Methods Based on Continuous Distributions of the Solvent, Chem. Rev. 1994, 94, 2027–2094. 22. Rao, S.V.; Narayana, R.D.; Akkara, J.A.; DeCristofano, B.S.; Rao, D.N. Dispersion studies of non-linear absorption in C60 using Z-scan, Chem. Phys. Lett. 1998, 297, 491-98. 23. Seilmeier, A.; Keiser, W. Ultrashort intramolecular and intermolecular vibrational energy transfer of polyatomic molecules in liquids, Ultrashort laser Pulses chapter, Topic in applied physics. 1993, 60, 279-317. 24. Yὕksek, M.; Elmali, A.; Durmus, M.; Yaglioglu, H.G.; Unver, H.; Nyokong, T. Good optical limiting performance of indium and gallium phthalocyanines in a solution and co-polymer host. J. Opt. 2010, 12, 015208. 25. Zhang, Y.; Wang, J.; Zhao, Q.; Gray, G. M.; Lawson, C. M. Five-energy level computer

model

for

fitting

Z-scan

measurements

in

disubstituted

chalcogenidodiphenylphosphino bithiophenes, Nonlinear Optics 2015, NW4A23. 26. Pawlicki, M.; Collins, H. A.; Denning, R. G.; Anderson, H. L. Two‐Photon Absorption and the Design of Two‐Photon Dyes. Angew Chemie Int Edition 2009, 48, 3244-3266. 27. Mack, J.; Stillman, M. J. Assignment of the optical spectra of metal phthalocyanine anions, Inorganic Chemistry 1997, 36.3, 413-425. 28. Shirk, J. S.; Pong, R. G. S.; Flom, S. R.; Heckmann, H.; Hanack, M. Effect of Axial

Substitution

on

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Indium

Phthalocyanines. The Journal of Physical Chemistry A 2000, 104, 1438–1449. 16 ACS Paragon Plus Environment

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Figures and Schemes: Scheme 1: Reaction pathway for β-SnOtBpPc. Scheme 2: Reaction pathway for α-SnOtBpPc. Scheme 3: The Five orbital model. Five level energy diagram explaining the dynamic of the excited state population (upward arrows), non-radiative relaxation (dashed arrows) in the studied complexes. Figure 1: TDDFT and MCD/Uv vis spectra of β-SnOtBpPc (left) and α-SnOtBpPc (right) in THF Figure 2: Michl’s frontier orbitals of α-SnOtBpPc (top) and β –SnOtBpPc (bottom). Figure 3: Ground state absorption (black), fluorescence emission (blue) and excitation (red) for β –SnOtBpPc in THF. Figure 4: Fluorescence decay curve for β-SnOtBpPc, obtained in THF Figure 5: Z-scan of (A) α-SnOtBpPc (top) and its fitting of q0 (zs) (bottom) and (B) βSnOtBpPc (top) and its fitting (bottom). The experimental results were obtained in toluene. Figure 6 The Imaginary component of the susceptibility of (A) β-SnOtBpPc and (B) α-SnSPPc vs solvent polarity. Figure 7: Experimental (points) and theoretical (solid line) z-scan transmittance plot based on the five energy level model for α-SnOtBpPc. The experimental results were obtained in toluene. Figure 8: Energy level diagram of (A) α-SnOtBpPc and (B) β-SnOtBpPc 17 ACS Paragon Plus Environment


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

Scheme 1: Reaction pathway for β-SnOtBpPc.


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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


Scheme 2: Reaction pathway for α-SnOtBpPc. Sn ).*

*.

Tn

S1 )k

"#

+. S0

)*+

,*,.

),,. T1

),*+

Scheme 3: The Five orbital model. Five level energy diagram explaining the dynamic of the excited state population (upward arrows), non-radiative relaxation (dashed arrows) in the studied complexes.



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 20 of 31

Figure 1: TDDFT and MCD/Uv vis spectra of β-SnOtBpPc (left) and α-SnOtBpPc (right) in THF.

S

A

S

A

-A

-A


-S

-S

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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


Figure 2: Michl’s frontier orbitals of α-SnOtBpPc (top) and β –SnOtBpPc (bottom).

Figure 3: Ground state absorption (black), fluorescence emission (blue) and excitation (red) for β –SnOtBpPc in THF.



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

Figure 4: Fluorescence decay curve for β-SnOtBpPc, obtained in THF.

(A)


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(B)

Figure 5: Z-scan of (A) α-SnOtBpPc (top) and its fitting of q0 (zs) (bottom) and (B) βSnOtBpPc (top) and its fitting (bottom). The experimental results were obtained in toluene.

Figure 6 Imaginary component of susceptibility of (A) β-SnOtBpPc and (B) αSnSPPc vs solvent polarity.



1.05

Transmitance

1 0.95 0.9 0.85 0.8 0.75 0.7 -20

-15

-10

-5

0

5

10

15

20

Zmm

1.05 1

Transmitance

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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0.95 0.9 0.85 0.8 0.75 0.7 -20

-15

-10

-5

0

Zmm

5

10

15

20

Figure 7: Experimental (points) and theoretical (solid line) z-scan transmittance plot based on the five energy level model for α-SnOtBpPc. The experimental results were obtained in toluene.


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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


Figure 8: Energy level diagram of (A) α-SnOtBpPc and (B) β-SnOtBpPc



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

Table 1: TD-DFT calculation results describing the absorption spectrum for Pcs(Q and B bands) as well as the transitions that give rise to these absorptions. Wavefunction=e

#b

Calcc

Expd

1

---

---

---

---

---

Ground state

2

15.8

655

(0.51)

14.9

704

74% a → -s; 4% s → -s; 7% H−6 (2a2u) → -s; …

3

16.0

655

(0.51)

14.9

704

74% a → -a; 7% H−6 (2a2u) → -a; 3% s → -a; …

9

23.2

431

(0.19) 25.0

~400

10

23.2

430

(0.02)

15

25.7

388

(0.24)

72% s → -s; … 72% s → -a; … 53% H−8 (2a1u) → -a; 40% H−6 (2a2u) → -s; … 28.6

389

β-SnOtBpPc

~350 56% H−8 (2a1u) → -s; 38% H−6 (2a2u) → -s; …

16

25.9

(0.10)

#b

Calcc

1

---

---

---

---

---

Ground state

2

14.8

674

(0.49)

13.6

731

75% a → -a; 7% a → -s; 4% s → -s; 2% H−6 (2a2u) → -s; …

3

14.8

674

(0.49)

13.6

731

75% a → -s; 7% a → -a; 2% s → -a; 2% H−6 (2a2u) → -a; …

9

20.5

486

(0.13) 25.0

~400

10

20.5

486

(0.13)

15

25.0

401

(0.11)

25.0

401

(0.11)

α-SnOtBpPc

87% s → -s; 7% H−2 (1b1u) → -a; … 87% s → -a; … 52% H−7 (2a1u) → -a; 37% H−6 (2a2u) → -s; … 28.6

16

Wavefunction=e

Expd

~350 52% H−7 (2a1u) → -s; 37% H−6 (2a2u) → -s; …

a − Band assignment described in the text. b − The number of the state assigned in terms of ascending energy within the TD-DFT calculation. c − Calculated band energies (103.cm−1), wavelengths (nm) and oscillator strengths in parentheses (f). d − Observed energies (103.cm−1) and wavelengths (nm) e − The wave functions based on the eigenvectors predicted by TD-DFT. One-electron transitions associated with Michl’s perimeter model are highlighted in bold. H and L refer to the HOMO and LUMO, respectively. When the H and L nomenclature is used the symmetry label for the corresponding MO in the π-systems of D4h MPc complexes is provided in parentheses where applicable.


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Table 2: Fluorescence and UV/absorption data.

λmax

(nm)

Abs

Em

Exc

τ(ns)

Chloroform

732

755

733

4.85

±

0.02

0.102

±

0.045

7.64E-28

Dichloromethane

731

754

731

3.05

±

0.01

0.01

±

0.122

9.56E-29

Tetrahydrofuran

727

750

727

4.13

±

0.02

0.13

±

0.072

1.14E-27

Toluene

728

751

729

5.13

±

0.02

0.2261 ±

0.134

1.66E-27

Chloroform

708

726

710

4.52

± 0.02

0.008

±

0.054

5.99E-29

Dichloromethane

708

725

709

5.55

± 0.02

0.010

±

0.067

9.71E-29

Tetrahydrofuran

704

721

705

4.37

± 0.02

0.007

±

0.055

6.59E-29

Toluene

707

722

706

3.43

± 0.01

0.008

±

0.089

5.87E-29

Pc

φ(ns)

Vm

α-SnOtBpPc

β-SnOtBpPc



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 28 of 31

Table 3: Q0, ZR and Beta for α-SnOtBpPc and β-SnOtBpPc in different solvents.

Q0

l [m/W]10-10

ZR[mm]

α-SnOtBpPc

Toluene

0.197 ± 0.033

3.289

± 0.525

0.977

± 0.327

Chloroform

0.286 ± 0.077

3.537

± 0.387

1.471

± 0.257

Dichloromethane

0.302 ± 0.019

3.752

± 0.618

1.673

± 0.280

Tetrahydrofuran

0.365 ± 0.118

3.673

± 0.247

1.963

± 0.553

Toluene

0.638

± 0.014

4.112

± 0.506

3.882

± 0.563

Chloroform

0.664

± 0.072

4.723

± 0.761

4.664

± 1.088

Dichloromethane

0.723

± 0.056

3.804

± 0.339

4.080

± 0.655

Tetrahydrofuran

0.688

± 0.088

6.159

± 1.048

6.340

± 1.850

β-SnOtBpPc


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Table 4:

List of the imaginary component of the third-order nonlinear optical

susceptibility and second-order hyperpolarizability (Im(χ3) and Im(γ)) in different solvents. Phthalocyanine solvent

Im(χ3)[esu]x10-10

Im(γ)[esu]x10-30

α-SnOtBpPc Toluene

1.54 ±

0.04

3.30 ±

0.10

Chloroform

1.47 ±

0.06

3.16 ±

0.12

Dichloromethane

1.70 ±

0.04

3.65 ±

0.11

Tetrahydrofuran

2.07 ±

0.11

4.44 ±

0.23

β-SnOtBpPc Toluene

3.96 ±

0.16

8.51 ±

0.21

Chloroform

4.66 ±

0.21

11.10 ±

0.45

Dichloromethane

4.64 ±

0.26

9.97 ±

0.54

Tetrahydrofuran

6.55 ±

0.32

14.11 ±

0.68



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 30 of 31

Table 5: Imaginary component of second-order hyperpolarizability (Im(γ)), as well as the 2PA, singlet and triplet excited state cross-sections (,GH ,

and

m respectively) at 532 nm, in toluene. Pc

Im(γ)[esu]ngfWog

@pBC [GM*]

@D A ngfWAf

@E A ngfWAf

α-SnOtBpPc

3.30

64.30

0.00445

0.22

β-SnOtBpPc

8.51

456.65

1.05x10-08

0.41

Five level orbital NLO fit results sorted by Im(γ). *1 GM=10-50cm4 s photon−1 Table 6: Ground state cross-section (b ) and excited state cross-section (R ) as well as their ratio and difference, all at 532 nm, in toluene. Pc

@F qA ngfWgr @h qA ngfWgs @h /@F @h −@F [cm2]ngfWgs

α-SnOtBpPc

4.28

2.22

β-SnOtBpPc

4.24

4.08

5.14

1.77

9.62

3.65

Cross-section analysis of the SnPcs.

Table 7: The energy difference between LUMO and the virtual state (∆) using a 532 nm laser, in toluene. The energy from ground state to intermediate state (Egi), the frequency of excitation (ν), Plank’s constant (h). Pc Egi[nm] Egi [eV] ν [x1014 Hz] h (eV.s x10-14)

∆=

hFu −g vw

α-SnOtBpPc

731

1.696

5.635

0.4136

-0.272

β-SnOtBpPc

704

1.759

5.635

0.4136

-0.245


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Solvent Effect on the Third-Order Nonlinear Optical Properties of Î±

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