Kamlet-Taft and Catalán solvatochromism of some π-expanded phenanthrimidazole derivatives - DFT analysis

Article abstract of DOI:10.1016/j.saa.2014.04.169

Some π-expanded phenanthrimidazole derivatives have been synthesised and characterised by different spectral techniques. Kamlet-Taft and Catala?n solvatochromism of synthesised phenanthrimidazole derivatives have been analysed. Non-linear optical (NLO) an

Full text of DOI:10.1016/j.saa.2014.04.169

Accepted Manuscript
Kamlet-Taft and Catalán solvatochromism of some π-expanded phenanthrimi-
dazole derivatives – DFT analysis
J. Jayabharathi, P. Ramanathan, V. Thanikachalam, A. Arunpandiyan
PII:
S1386-1425(14)00742-2
http://dx.doi.org/10.1016/j.saa.2014.04.169
SAA 12133
DOI:
Reference:
Spectrochimica Acta Part A: Molecular and Biomo-
lecular Spectroscopy
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Accepted Date:
10 February 2014
17 April 2014
23 April 2014
Please cite this article as: J. Jayabharathi, P. Ramanathan, V. Thanikachalam, A. Arunpandiyan, Kamlet-Taft and
Catalán solvatochromism of some π-expanded phenanthrimidazole derivatives – DFT analysis, Spectrochimica Acta
Part A: Molecular and Biomolecular Spectroscopy (2014), doi: http://dx.doi.org/10.1016/j.saa.2014.04.169
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1
Kamlet-Taft and Catalán solvatochromism of some π-expanded phenanthrimidazole
derivatives – DFT analysis
J. Jayabharathi*, P. Ramanathan, V. Thanikachalam, A. Arunpandiyan
Department of Chemistry, Annamalai University, Annamalainagar 608 002, Tamilnadu, India.
* Address for correspondence
Dr. J. Jayabharathi
Professor of Chemistry
Department of Chemistry
Annamalai University
Annamalainagar 608 002
Tamilnadu, India.
Tel: +91 9443940735
E-mail: jtchalam2005@yahoo.co.in

2
Kamlet-Taft and Catalán solvatochromism of some π-expanded phenanthrimidazole
derivatives – DFT analysis
J. Jayabharathi*, P. Ramanathan, V. Thanikachalam, A. Arunpandiyan
Department of Chemistry, Annamalai University, Annamalainagar 608 002, Tamilnadu, India.
Abstract
Some π-expanded phenanthrimidazole derivatives have been synthesised and characterised
by different spectral techniques. Kamlet-Taft and Catalán solvatochromism of synthesised
phenanthrimidazole derivatives have been analysed. Non-linear optical (NLO) and natural
bond orbital (NBO) analysis have been made by ab initio method to show intramolecular
interactions. The energies of the HOMO and LUMO levels, the molecular electrostatic
potential (MEP) energy surface, NBO studies have exploited the existence of intramolecular
charge transfer (ICT) within the molecule.
Keywords: Kamlet-Taft; Catalán; Solvatochromism; π-expanded phenanthrimidazole; DFT.

3
1. Introduction
The electronic absorption and emission characteristics are strongly sensitive to organic
ligand and also to the solvent [1-3]. In order to correlate the polarity influence of the solvent
on the absorption and fluorescence emission wavelengths, the Kamlet and Taft scale play a
highly significant role [4, 5]. The incorporation of the NLO chromophore converts the
phenanthrimidazole ring into polyamides leading to NLO side chain polymers [6]. Most π-
conjugated systems play a major role in determining second-order NLO response [7].
Organic materials with non-linear optical (NLO) properties are mainly concentrated on
molecules with donor–acceptor π-conjugation (D-π-A) and deals with the substituent effects
on the degree of π-conjugation, steric hindrance and the hyperpolarisability of the substances
[8]. Nowadays there is an insufficient understanding for designing optimal NLO materials,
even certain classes of D-π-A compounds were theoretically studied. Besides, geometrical
arrangement of the molecules in the solid state, their interaction and other physicochemical
properties live strong intramolecular charge-transfer absorptions and engineering possibilities
are also important [9]. Therefore, in continuation of our research [10a-g] herein we report the
Kamlet-Taft and DFT analysis of NLO active π–expanded phenanthrimidazole derivatives.
2. Experimental
2.1. Spectral measurements
The ultraviolet-visible (UV-vis) spectra of the phenanthrimidazole derivatives were
measured in an UV-vis spectrophotometer (Perkin Elmer Lambda 35) and corrected for
background absorption due to solvent. Photoluminescence (PL) spectra were recorded on a
(Perkin Elmer LS55) fluorescence spectrometer. Proton and decoupled NMR spectra were
recorded at 400 and 100 MHz respectively, on Bruker 400 MHz NMR spectrometer. Mass
spectra were recorded on a Varian Saturn 2200 GCMS spectrometer. The lifetime spectra
have been recorded on Fluorocube-01-NL lifetime system provided with emission

4
monochromator and diode excitation. Cyclic voltammetry (CV) analysis was performed by
using CHI 604C electrochemical analyzer, working electrode is Glassy carbon electrode.
Reference electrode, silver/ silver chloride (Ag/AgCl).
2.2. Synthesis of polysubstituted phenanthrimidazoles (1-6)
A mixture of naphthaldehyde (1 mmol), phenanthrene-9,10-dione (1 mmol), aniline
(1 mmol), ammonium acetate (1mmol) and InF3 (1 mol%) was stirred at 80 °C and the
progress of the reaction was monitored by TLC. After completion of the reaction, the mixture
was cooled, dissolved in acetone and filtered (Scheme 1). The product was purified by
column chromatography using benzene: ethyl acetate (9:1) as the eluent [10a-g]. The newly
1
synthesised phenanthrimidazoles have been characterised by CHN analysis, H and 13C NMR
and mass spectra.
2.2.1. 2-(Naphthalen-1-yl)-1H-phenanthro[9,10-d]imidazole (1)
M.p. 262- 263 ºC., Anal. calcd. for C25H16N2: C, 87.18; H, 4.68; N, 8.13. Found: C, 87.16; H,
4.67; N, 8.12. 1H NMR (400 MHz, DMSO):  10.41 (s, 1H), 7.37 (s, 4H), 8.77 (d, J = 7.2 Hz,
13
3H), 7.90 (d, J = 8.0 Hz, 2H), 7.82 (d, J = 7.2 Hz,1H), 7.66 (t, 4H), 7.54-7.45 (m, 3H). C
NMR (400 MHz, CDCl3):  121.83, 123.78, 124.97, 125.47, 125.89, 126.38, 127.12, 127.29,
127.58, 127.88, 128.37, 128.47, 130.16, 131.30, 133.92, 148.87. MS: m/z. 344.40 [M+],
Calcd. m/z. 344.40.
2.2.2. 2-(Naphthalen-1-yl)-1-phenyl-1H-phenanthro[9,10-d]imidazole (2)
M.p. 265-267 ºC., Anal. calcd. for C31H20N2: C, 88.54; H, 4.79; N, 6.66. Found: C, 88.52; H,
1
4.78; N, 6.65. H NMR (400 MHz, DMSO):  8.89 (d, J = 7.6 Hz, 1H), 8.80 (d, J = 8.4 Hz,
1H), 8.75 (d, J = 7.6 Hz, 1H), 7.99 (d, J = 5.6 Hz, 1H),7.83 (d, J = 7.6 Hz, 2H), 7.74 (t, 1H),
7.67 (t, 1H), 7.53 (t, 1H), 7.48-7.43 (m, 3H), 7.35-7.29 (m, 6H). 13C NMR (400 MHz,
CDCl3):  121.07, 122.89, 123.01, 123.18, 124.16, 124.48, 125.02, 125.65, 126.02, 126.17,
126.34, 126.88, 127.38, 127.44, 128.05, 128.15, 128.34, 128.49, 129.28, 129.48, 129.55,

5
129.73, 133.21, 133.47, 137.38, 138.04, 150.48. MS: m/z. 420.80 [M+], Calcd.,
m/z. 420.50.
2.2.3. 2-(Naphthalen-1-yl)-1-p-tolyl-1H-phenanthro[9,10-d]imidazole (3)
M.p.248- 249 ºC., Anal. calcd. for C32H22N2: C, 88.45; H, 5.10; N, 6.45. Found: C, 88.41; H,
1
5.07; N, 6.42. H NMR (400 MHz, DMSO):  2.32 (s, 3H), 8.88 (d, J = 7.6 Hz, 1H),
8.79 (d, J = 8.4 Hz, 1H), 8.73 (d, J = 8.0 Hz, 1H), 7.96 (d, J = 7.2 Hz, 1H), 7.80 (d, J = 8.0 Hz,
2H), 7.20 (d, J = 7.6 Hz, 2H), 7.10 (d, J = 8.0 Hz, 2H), 7.71 (t, 1H), 7.65 (t, 1H), 7.53 (t, 1H),
7.43 (q, 3H) 7.35-7.24 (m, 4H). 13C NMR (400 MHz, DMSO):  21.31, 121.11, 122.87,
123.12, 123.20, 124.14, 124.50, 124.70, 125.00, 125.10, 125.62, 126.04, 126.14, 126.35,
126.83, 127.38, 127.53, 127.77, 128.15, 128.34, 128.39, 129.28, 129.47, 129.67, 130.20,
133.23, 133.44, 133.76, 135.32, 137.27, 139.29, 150.63. MS: m/z. 434.10 [M+], Calcd.
m/z. 434.53.
2.2.4. 1-(4-Methoxyphenyl)-2-(naphthalen-1-yl)-1H-phenanthro[9,10-d]imidazole (4)
M.p. 231-233 ºC., Anal. calcd. for C32H22N2O: C, 85.31; H, 4.92; N, 6.22; O, 3.55. Found:
1
C, 85.30; H, 4.91; N, 6.21; O, 3.54. H NMR (400 MHz, DMSO):  3.72 (s, 3H),
8.96 (d, J = 8.4 Hz, 1H), 8.91 (d, J = 8.4 Hz, 1H), 8.66 (d, J = 7.6 Hz, 1H), 7.89 (d, J = 8.0 Hz,
1H), 7.76 (d, J = 7.2 Hz, 1H), 7.57 (d, J = 7.6 Hz, 1H), 7.38 (t, 1H), 7.20 (d, J = 8.0 Hz, 1H),
6.94 (d, J = 8.4 Hz, 2H), 7.96 (t, 2H), 7.69 (t, 2H), 7.55-7.42 (m, 5H). 13C NMR
(400 MHz, DMSO):  55.28, 114.62, 120.27, 121.98, 122.59, 123.66, 124.42, 124.67, 125.19,
125.60, 125.78, 126.20, 126.69, 126.82, 126.86, 127.24, 127.42, 127.64, 128.04, 128.09,
128.29, 128.41, 129.50, 129.52, 129.72, 129.95, 132.35, 132.76, 136.28, 150.47, 159.47. m/z.
450.50 [M+], Calcd. m/z. 450.53.
2.2.5. 1-(3,5-Dimethylphenyl)-2-(naphthalen-1-yl)-1H-phenanthro[9,10-d]imidazole (5)
M.p. 261-262 ºC., Anal. calcd. for C33H24N2: C, 88.36; H, 5.39; N, 6.25. Found: C, 88.35; H,
5.38; N, 6.24. 1H NMR (400 MHz, DMSO):  2.17 (s, 6H), 8.96 (d, J = 8.0 Hz, 1H), 8.91 (d, J

6
= 8.0 Hz, 1H), 8.64 (d, J = 7.6 Hz, 1H), 7.97 (t, 2H), 7.91 (d, J = 7.2 Hz, 1H), 7.76 (d, J = 7.2
Hz, 1H), 7.74 (d, J = 6.4 Hz, 2H), 7.08 (s, 1H), 7.16 (t, 2H), 7.36-7.40 (m, 3H),7.60-7.48 (m,
3H). 13C NMR (400 MHz, DMSO):  20.54, 120.36, 121.99, 122.45, 123.66, 124.42, 124.66,
125.22, 125.44, 125.66, 125.83, 126.06, 126.22, 126.33, 126.71, 126.76, 127.00, 127.23,
127.45, 127.62, 127.90, 128.04, 128.29, 128.40, 129.54, 131.01, 132.28, 132.75, 136.27,
137.28, 138.90, 150.06. MS: m/z. 448.60 [M+], Calcd. m/z. 448.55.
2.2.6. N,N-Dimethyl-4-(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)naphthalen-1-amine
(6)
M.p. 258-260 ºC., Anal. calcd. for C33H25N3: C, 85.50; H, 5.44; N, 9.06. Found: C, 85.49;
H, 5.43; N, 9.05. 1H NMR (400 MHz, DMSO):  3.46 (s, 6H), 9.23 (d, J = 8.4 Hz, 1H), 8.87
(s, 2H), 8.69 (s, 1H), 8.61 (s, 1H), 8.16 (d, J = 7.2 Hz, 1H), 8.11 (d, J = 8.0 Hz, 1H), 8.07 (dd,
J = 8.0 Hz, 1H), 7.78-7.62 (m, 8H), 7.34 (s, 2H). 13C NMR (400 MHz, DMSO):  43.88,
122.02, 122.42, 123.78, 124.03, 124.30, 124.69, 125.28, 126.32, 126.40, 126.88, 127.05,
127.15, 127.63, 127.77, 128.28, 128.38, 128.67, 128.99, 129.08, 129.25, 129.75, 130.61,
131.13, 133.65, 135.21, 135.35, 136.79, 137.02, 149.04, 151.82, 178.94, 189.42, 194.35. MS:
m/z. 463.40 [M+], Calcd. m/z. 463.57.
2.3. Computational details
Quantum chemical calculations have been used to carry out the optimized geometry,
NBO, NLO, MEP and HOMO-LUMO analysis with Guassian-03 program [11].
3. Results and discussion
3.1 Characterisation of phenanthrimidazole derivatives
All the aromatic protons of 1 are deshielded in the range of 7.45-10.41 ppm and their
corresponding carbons are resonate in the range of 121-148 ppm. For compound 2 the peak in
the range 8.89-7.29 is assigned to aromatic protons and the peak in the range 121-150ppm is
assigned to all aromatic carbons of the compound. The methyl protons of

7
phenanthrimidazole 3 is shielded and appered at 2.32 ppm and the methyl carbon is appeared
at 21.31ppm. All the aromatic protons are deshielded in the range of 7.24-8.88 ppm and their
corresponding carbons are resonate in the range of 121-150 ppm. The methoxy protons of
phenanthrimidazole 4 is deshielded when compared with phenanthrimidazole 3 due to the
electronegative oxygen atom. The sharp singlet at 3.72 ppm is assigned to methoxy protons
and the methoxy carbon is resonate at 55.28ppm. All the aromatic protons are deshielded in
the range of 7.42-8.96 ppm and their corresponding carbons are resonate in the range of 114-
159 ppm. The methyl protons of phenanthrimidazole 5 is shielded and appered as singlet at
2.17ppm and the methyl carbon is appeared at 20.54ppm. All the aromatic protons are
deshielded and appeared in the range of 7.48-8.96 ppm and their corresponding carbons are
resonate in the range of 120-150 ppm. The methyl protons of N, N -dimethyl
phenanthrimidazole 6 is shielded and appeared as singlet at 3.46 ppm and their methyl
carbon is appeared at 43.88 ppm. The deshielding magnitude of methyl signals in both proton
and C13 is due to the electronegativity of nitrogen atom. All the aromatic protons are
deshielded and appeared in the range of 7.62-9.23 ppm and their corresponding carbons are
resonate in the range of 122-194 ppm
3.2. Solvatochromism
The absorption and fluorescence spectra have been recorded in all polar and non polar
solvents from hexane to water. Solvent polarity, mainly affect the photophysical properties of
compounds. Different scales for such parameters can be found in the literature, Taft et al. [12]
propose the π*, α and β scales, to describe polarity, H-bond donor capacity and electron
donor ability shown as, y y0 + aαα + bββ + cπ* π*, Catalán et al. [13] suggest the SPPN, SA
=
and SB scales to described the polarity/polarizability, the acidity and basicity of the solvents
as shown as, y y0 + aSASA + bSBSB + cSPPSPP. The correlation of the absorption and
=
fluorescence wave numbers obtained by the multi-component linear regression employing the

8
Taft and Catalán solvent parameters with the experimental values given in Table S1. The
coefficient affecting the absorption and emission of π-expanded phenanthrimidazole
derivatives is that describing the polarity/polarizability of the solvent [Cπ* or CSPPN] have
positive value correlating the solvatochromic shifts with the solvent polarity. The coefficient
controlling the H-donor capacity or acidity of the solvent [Cα or CSA] have a positive value.
Therefore the solvent acidity does not play an important role in both absorption and emission.
The coefficient controlling the electron releasing ability or basicity of the solvent [Cβ or CSB]
have higher negative value for emission than absorption. This is interpreted in terms of
stabilization of the resonance structures of the chromophores as shown below,
Due to the possible electronic shift in the phenanthrimidazole derivatives the positive
charge may be located at the azomethine nitrogen atom and it will be stabilized in basic
solvents.
3.3. Vibrational analysis
The IR bands of aromatic stretching vibrations are appear in the
frequency range around 3290 cm-1 (Figure1). The observed bands in the range 271-1011 cm-
1
are assigned to in-plane C-H bending of the phenyl ring. The observed bands in the range
630 -705 cm-1 are assigned to out-of-plane C-H wagging on the phenyl ring [14]. The IR
frequency in the range 1011-1522 cm-1 are mainly due to the C-C stretching vibration of aryl
ring and phenanthrimidazole ring [15]. The bending vibration of the phenyl ring was
observed around 620 cm-1. The stretching vibration of CO appears at 1273 cm-1 and the

9
band at 3416 cm-1 is strongly coupled with in-plane wagging of NH stretching vibration.
The prominent vibrations are displayed in Table 2.
3.4. Second harmonic generation (SHG) studies
Second harmonic signal of 40 mV - 45 mV were obtained for the phenanthrimidazole
derivatives by an input energy of 4.1mJ/pulse. But the standard KDP crystal gave a SHG
signal of 110mV/pulse for the same input energy. The second order non-linear efficiency
will vary with the particle size of the powder sample [16, 17]. On a molecular scale, the
extent of charge transfer (CT) across the NLO chromophores determines the level of SHG
output, the greater the CT and the larger the SHG output.
3.5. Comparison of µβo
Theoretical investigation plays an important role to know the structure-activity
relationship, which is able to help in designing novel NLO chormophores. The first
hyperpolarizability (β) and dipole moment (μ) of the phenanthrimidazole chromophores have
been calculated by using Gaussian 03 package [11]. From Table 1, it is found that the
π-expanded phenanthrimidazole chromophores show larger µβo values, which is attributed to
the positive contribution of their conjugation. This chromophores exhibits larger non-linearity
and its absorption is shifted when compared with unsubstituted phenanthrimidazole which
indicate that the hyperpolarisability is a strong function of the absorption maximum. The β
values computed here might be correlated with UV-visible spectroscopic data in view of a
future optimization of the microscopic NLO properties. The band centered around 340 nm
exhibits a solvatochromic shift characteristic of a large dipole moment and frequently
suggestive of a large hyperpolarisability. These compounds show shift in absorption with
increasing solvent polarity accompanied with the upward shifts non-zero values in the β-
components [18-21].

10
3.6. Octupolar and dipolar components
These phenanthrimidazole derivatives possess appropriate ratio of off-diagonal versus
diagonal  tensorial component (r =xyy/xxx) [r = 0.66 (1), 0.54 (2), 0.16 (3), 0.34 (4), 1.28
(5) and 2.37 (6)] which reflects the inplane non-linearity anisotropy. The -tensor [22] can be
decomposed in a sum of dipolar (
) and octupolar (
) tensorial components and the
ratio of these two components strongly depends on their ‘r’ ratios. The zone for r > r2 and r <
r1 corresponds to a molecule of octupolar and dipolar respectively. The critical values for r1
and r2 are (1- 3)/ 3 3+1) = -0.16 and ( 3+1)/ 3( 3-1) = 2.15, respectively. Complying
with the Pythagorean theory and the projection closure condition, the octupolar and dipolar
2
components of the  tensor can be described as:
+ [( (1/4)[(
yxx)2]; xyy)2 +[( yxx)2].
(3/4)[(
)
xyy
xxx
+
yyy +
xxx - 3
yyy -
2D
2D
The parameter
=
is convenient to compare the relative magnitudes of the
2D
octupolar and dipolar components of. The observed positive small
value 1 (0.71), 2
(0.38), 3 (0.53), 4 (0.56), 5 (0.64) and 6 (1.11) reveals the iii component cannot be zero and
these are dipolar components. Since most of the practical applications for second order NLO
chromophores are based on their dipolar components and this strategy is more appropriate for
designing highly efficient NLO chromophores.
3.7. Natural Bond Orbital (NBO) analysis
NBO analysis [23] have been performed for these π-expanded phenanthrimidazole
derivatives at DFT/B3LYP/6-31++G (d,p) level in order to elucidate the intramolecular,
charge transfer within the molecule and the results have been displayed in Tables S2–S7.
Several donor-acceptor interactions have been observed and among the strongly occupied
NBOs, the most important delocalization sites are in the π system and in the lone pairs (n) of
the oxygen, fluoro and nitrogen atoms. The σ system shows some contribution to the

11
delocalization, and the important contributions to the delocalization corresponds to the donor-
acceptor interactions for the phenanthrimidazole derivatives are C1–C2 → C3–C4, C1–C2 →
C5–C6, C3–C4 → C1–C2, C3–C4 → C5–C6, C3–C4 → C7–C10, C3–C4 → C8–C9, C5–
C6→ C1–C2, C5–C6 → C3–C4, C7–C10 → C3–C4, C7–C10→ C8–C9, C7–C10 → C15–
N16, C7–C10 → C16–N17, C8–C9 →C3–C4, C8–C9 → C7–C10, C8–C9 → C11–C12, C8–
C9→ C13–C14. The charge distribution of the phenanthrimidazole derivatives have been
calculated from the atomic charges by NBO and NLO analyses (Figure S1). These methods
reveal among the nitrogen atoms, azomethine nitrogen is considered as more basic site [21,
24]. The charge distribution shows that the more negative charge is concentrated on
azomethine nitrogen atom whereas the partial positive charge resides at hydrogen atoms.
3.8. Molecular electrostatic potential map (MEP) and electronic properties
Molecular electrostatic potential (MEP) maps (Figure S2) show the distribution of charges
across the surface of a molecule. This diagram is used to understand the reactive behaviour of
a molecule, in that negative regions can be regarded as nucleophilic centres, whereas the
positive regions are potential electrophilic sites. The MEP map of the phenanthrimidazole
derivatives show that the nitrogen, fluoro and oxygen atoms represent the most negative
potential region. The hydrogen atoms bear the positive charge and the predominance of green
region in the MEP surface corresponds to a potential halfway between the two extremes red
and dark blue colour.
The HOMO orbital acts as an electron donor and the LUMO orbital acts as the electron
acceptor. The 3D plots of the frontier orbitals HOMO and LUMO is shown in Figure S3. The
HOMO→LUMO transition implies the intramolecular charge transfer takes place [26] within
the molecule. The energy gap (Eg) of these phenanthrimidazole derivatives have been
calculated from the HOMO and LUMO levels (Table S8) which explains the probable charge
transfer inside the chromophore. From the onset oxidation potential (Eox) and the onset

12
reduction potential (Ered) of the BPBI, HOMO and LUMO energy levels have been calculated
according to the following equations, HOMO = −e(Eox + 4.71) (eV); LUMO = −e(Ered
+
4.71) (eV). Experimental HOMO-LUMO energies are in good agreement with the theoretical
values (Table S8). However, from the theoretical values it can be found that most of the
optimized bond lengths, bond angles and dihedral angles are slightly higher than that of
Experimental values. These deviations can be attributed to the fact that the theoretical
calculations were aimed at the isolated molecule in the gaseous phase and the XRD results
are on at the molecule in the solid state.
4. Conclusions
Solvent effect on phenanthrimidazole derivatives have been analysed by Taft and Catalán
approach. The observed solvatochromic shift is a characteristic of a large dipole moment and
frequently suggestive of a large hyperpolarizability. The calculated dipolar and octupolar
components supported these phenanthrimidazole derivatives are efficient NLO
chromophores. The observed positive small 2D value show that the iii component cannot be
zero and these are dipolar components.
5. Acknowledgments
One of the authors Prof. J. Jayabharathi is thankful to DST [No. SR/S1/IC-73/2010],
DRDO (NRB-213/MAT/10-11), UGC (F. No. 36-21/2008 (SR)) and CSIR (NO 3732/NS-
EMRII) for providing funds to this research study.

13
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16
Figure Captions
Figure S1. Mulliken Charge distribution of 1-6 using NLO and NBO methods
Figure S2. MEP surface diagram of phenanthrimidazole derivatives 1-6.
Figure S3. HOMO-LUMO molecular orbitals of phenanthrimidazole derivatives 1-6.
Scheme 1. Possible mechanism for catalytic synthesis of phenanthrimidazoles

Table 1. Polarizability parameters electric dipolemoment (µ, D), polarizability α (x 10-31esu),
hyperpolarisability β (x 10-33esu) of π-expanded phenanthrimidazoles
Parameters
1
2
3
4
5
6
ꢀ
α
0.56
3.75
9.05
0.66
0.71
5.07
0.36
3.46
5.32
0.54
0.38
1.92
0.42
1.88
5.96
0.16
0.53
2.50
0.42
6.42
3.51
0.34
0.56
1.47
0.71
3.66
1.62
1.28
0.64
1.15
0.12
1.93
9.15
2.37
1.11
1.10
β
r
ꢀ2D
µβ0

Table 2. Vibrational analyses of compounds 1-6
Wavenumber (cm-1)
Compd.
(Ar-
(C-C)
In plane & Phenyl
(C-O)
(N-H)
Stretching)
3335-3451
Stretching Out plane (H) bending Stretching Stretching
1
2
3
4
5
6
1470-1522
1348-1727
1330-1727
1281-1697
1764
282-691
284-705
288-693
440-1020
1011
705
705
-
3416
3293-3446
3292-3447
3290-3445
3375-3521
3294-3485
-
-
-
-
-
-
620-693
681
-
1274
674
-
-
1349-1734
271-759
630-688

GRAPHICAL ABSTRACT

Highlights
 Kamlet- Taft and Catalan solvatochromic analysis of phenanthrimidazole derivatives
have been made.
 Ratio of off-diagonal versus diagonal  tensorial component reflects the inplane non-
linearity anisotropy and High efficient NLO chromophores
 Donor-acceptor interactions can be confirmed by NBO analysis
 HOMO→LUMO transition implies the presence of intramolecular charge transfer in
the chromophores