Luminescence feature of new 3,6-di(thiazolidin-5-one-2-yl)-carbazole derivative: synthesis, photophysical properties, density functional theory studies, and crystal shape effect

Article abstract of DOI:10.1002/bio.4013

A new carbazole chromophore conjugated with substituted thiazolidine-4-one (CzPT) was synthesized by applying the Knoevenagel reaction between 3,6-diformyl-N-hexylcarbazole and ethyl 2-aceto-2-(5-oxo-3-phenylthiazolidin-2-ylidene)acetate. The chemical structure of the new derivative (CzPT) was elucidated by spectral studies. The CzPT absorption spectra in different solvents exhibited a red shift for λ_max by increasing solvent polarity. Bands at 430–474 nm appeared and were attributed to intramolecular charge transfer with high π–π* characteristics. CzPT fluorescence spectra exhibited a red shift after increasing the solvent polarity. To understand the Stokes' shift ((Formula presented.) behaviour of the CzPT derivative referring to the polarity of solvents, Lippert–Mataga and linear solvation-energy relationship (LSER) models were employed in which the LSER exhibited respectable results compared with Lippert–Mataga (r² = 0.9707). Moreover, time-dependent density functional theory absorption spectra in hexane and dimethylformamide showed that λ_max had a major contribution in the highest occupied molecular orbital to lowest unoccupied molecular orbital transition in both solvents. In addition, the reduced uniformity of crystal features may lead to dislocation or anomalous arrangement of crystals with irregular spacing, which automatically enhances the optical properties of such crystals.

Full text of DOI:10.1002/bio.4013

Received: 2 December 2020
DOI: 10.1002/bio.4013
Revised: 5 January 2021
Accepted: 8 January 2021
R E S E A R C H A R T I C L E
Luminescence feature of new 3,6-di(thiazolidin-5-one-2-yl)-
carbazole derivative: synthesis, photophysical properties,
density functional theory studies, and crystal shape effect
Tahani M. Bawazeer1 | Ismail Althagafi1
| Moataz Morad1 | Alaa M. Munshi1
|
Abrar A. Bayazeed1 | Arwa Alharbi1 | Nashwa El-Metwaly1,2
1Department of Chemistry, College of Applied
Abstract
Sciences, Umm Al-Qura University, Makkah,
Saudi Arabia
A new carbazole chromophore conjugated with substituted thiazolidine-4-one (CzPT)
was synthesized by applying the Knoevenagel reaction between 3,6-diformyl-N-
hexylcarbazole and ethyl 2-aceto-2-(5-oxo-3-phenylthiazolidin-2-ylidene)acetate.
The chemical structure of the new derivative (CzPT) was elucidated by spectral stud-
ies. The CzPT absorption spectra in different solvents exhibited a red shift for λmax
by increasing solvent polarity. Bands at 430–474 nm appeared and were attributed
to intramolecular charge transfer with high π–π* characteristics. CzPT fluorescence
spectra exhibited a red shift after increasing the solvent polarity. To understand the
Stokes' shift (ΔꢀνÞ behaviour of the CzPT derivative referring to the polarity of sol-
vents, Lippert–Mataga and linear solvation-energy relationship (LSER) models were
employed in which the LSER exhibited respectable results compared with Lippert–
Mataga (r2 = 0.9707). Moreover, time-dependent density functional theory absorp-
tion spectra in hexane and dimethylformamide showed that λmax had a major contri-
bution in the highest occupied molecular orbital to lowest unoccupied molecular
orbital transition in both solvents. In addition, the reduced uniformity of crystal fea-
tures may lead to dislocation or anomalous arrangement of crystals with irregular
spacing, which automatically enhances the optical properties of such crystals.
2Chemistry Department, Faculty of Science,
Mansoura University, Mansoura, Egypt
Correspondence
Nashwa El-Metwaly, Chemistry Department,
College of Applied Sciences, Umm Al-Qura
University, 21955, Makkah, Saudi Arabia.
Email: n_elmetwaly00@yahoo.com;
nmmohamed@uqu.edu.sa
K E Y W O R D S
carbazole, DFT studies, energy gap, fluorescence, thiazolidine-5-one
1
|
INTRODUCTION
acceptor compounds with a polyaromatic core have had much interest
for use in electroluminescence (EL) devices due to their robust emis-
Fluorescence systems have been used to investigate small molecules
such as metal cations and other inorganic compounds.[1] Organic
light-emitting diodes (OLEDs) have wide scope for improvement as
highly efficient emitters.[2–4] The stability and emission of solid states
remain a significant advantage for organic compounds used as
OLEDs.[5,6] The sizable emission of combinations in solution usually
develops low value in solid-state reactions due to electron transition
and intermolecular energy,[7] therefore, the synthesis of compounds
with high emission efficiency in the solid state, is important.[8] Donor–
sions in the solid state.[9] Understanding the structure of fluorescent
compounds is important due to their wide application in the environ-
ment, biochemistry, and medical tenders, etc.[10–14] Many chemical
and biochemical molecules such as gases, neutral molecules, anions
and cations can be investigated using fluorescence techniques.[15,16]
Poly(1-amino naphthalene) has been synthesized and used as a
chemosensor to identify Fe3+ via a fluorometric method.[17] Four
fluorophores with a donor–acceptor structure with variable substitu-
tions at the imidazole moiety have been synthesized.[18] Using waste
904
© 2021 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/bio
Luminescence. 2021;36:904–913.

BAWAZEER ET AL.
905
foam, S/N-carbon quantum dots have been synthesized and pres-
ented different colours such as blue, blue–green, green, green–yellow
and yellow.[19] To date, despite the presence of a large number of
fluorescent molecular sensors for specific applications, there is still an
urgent need to prepare sensors with improved selectivity and small
effects on the environment.[20,21]
temperature. The reaction was poured into 100 ml ice-cold water and
the pH was adjusted to close to alkaline by adding saturated sodium
acetate solution. The solid product that collected was recrystallized
from ethanol to produce brown crystals with 72% yield (0.88 g).
M.p. 143–144ꢀC; literature m.p. 144–146ꢀC.[31]
In the absence of cations that may bind to the carbazole mole-
cule, the electron–donor–acceptor (EDA) moiety displays charge
transfer. Without complex formation via inorganic cations, the
electron-donating capacity of electron donors decreases and the moi-
ety does not reveal its charge transfer properties,[22–24] therefore
absorption of the noncomplexed moiety is hypsochromically shifted
compared with the complexed system.[25] Absorption of non-
complexed systems produced a very weak hypsochromic shift in the
fluorescence spectrum of the complexed moieties.[26] This can be
explained as follows: after excitation the electron-donating moiety in
the molecule is able to carry a positive charge, which results in fluo-
rescence close to that of the noncomplexed system.[27] Charge trans-
fer molecules with donor–acceptor moieties that bind by double
bonds also often act as cation indicators.[28] Carbazole derivatives are
good molecules for use in colour flat-panel displays.[29] Fluorescence
compounds have diverse and specific applications such as in chemical
sensors, biological detectors, and cosmic-ray detectors. Therefore,
based on studies mentioned above, the goal of this research was to
design and synthesize a new 3,6-di(thiazolidin-5-one-2-yl)-carbazole
derivative that had fluorescence or optical properties. Such properties
would allow it to have new applications, such as in special spectral
and computer studies. The effects of crystal shape and shell thickness
on the optical properties were also examined.
2.3
|
Synthesis of diethyl 2,20-(((9-hexyl-9H-
carbazole-3,6-diyl)bis(methanylylidene))-bis(5-oxo-
3-phenylthiazolidine-4,2-diylidene))bis
(3-oxobutanoate) (CzPT)
In a 100 ml RB flask, 3,6-diformyl-N-hexylcarbazole (1) (0.92 g,
3 mmol) was dissolved in 40 ml ethanol. Ethyl-2-aceto-2-(5-oxo-
3-phenylthiazolidin-2-ylidene)acetate (2) (1.83 g, 6 mmol) and three
drops of piperidine were added. The reaction components were
refluxed for 2 h and the product formed upon cooling was collected.
Recrystallization of this solid was achieved from ethanol as golden
crystals with 86% yield (2.27 g).
M.p. 211–212ꢀC. Infrared (IR) (KBr): 3051 (C–H aromatic), 2946,
2879 (C–H aliphatic), 1726 (C=O), 1684 cm−1 (broad, C=O). 1H NMR
(CDCl3): δ 0.81 (t, 3H, J = 7.00 Hz, CH3), 1.07–1.12 (m, 6H, –
CH2CH2CH2–), 1.22 (t, J = 7.00 Hz, 6H, 2 CH3), 1.83 (m, 2H, CH2),
2.37 (s, 6H, 2 COCH3), 4.15 (q, J = 7.00 Hz, 4H, OCH2), 4.51
(t, J = 7.00 Hz, 2H, NCH2), 7.38–7.91 (m, 16H, Ar–H), 8.04 ppm
(s, 2H, C=CH). Mass analysis (m/z, %): 882 (M+, 16.68), 590 (22.12),
479 (30.21), 454 (37.79), 434 (100.00), 401 (28.92), 368 (38.45),
279 (29.81), 128 (30.86), 116 (52.60), 68 (85.91). Analysis calculated
for C50H47N3O8S2 (882.06): C, 68.09; H, 5.37; N, 4.76%. Found: C,
68.28; H, 5.30; N, 4.87%.
2
|
EXPERIMENTAL
General
2.4
|
Density functional studies
2.1
|
The Gaussian 09 W program[30] was used for quantum chemical calcu-
lations of the CzPT derivative at density functional theory (DFT) level
Infrared spectra (KBr discs) were generated on a Thermo Scientific
Nicolet iS10 FTIR spectrometer. 1H nuclear magnetic resonance (NMR)
(500 MHz) spectra were obtained using a JEOL's NMR spectrometer in
deuterated chloroform (CDCl3). Mass spectroscopy was performed
using a Shimadzu Qp-2010 Plus (GC–MS) spectrometer. The Unicam
UV/Vis UV2 spectrometer was used to measure the electronic spectra
in different solvents in 1 cm silica cells. The emission spectra were
recorded on a PerkinElmer LS 55 fluorescence spectrometer.
with
Becke3–Lee–Yang–Parr
exchange-correlation
functional
(B3LYP)[31–33] and 6-311G++ basis set. The obtained positive fre-
quency values confirmed the stability of optimized geometry. The
ground-excited state properties in hexane and DMF were studied
using time-dependent DFT (TD-DFT)[34–36] at the B3LYP level in
which the polarizable continuum model using integral equation for-
malism variant (IEF-PCM)[37,38,40] was used as a solvent model. There-
fore, the obtained wavelengths were compared with that recorded
experimentally in UV–visible spectra. Gauss-View[39] and Gauss-Sum
2.2[40] software were utilized for determination of HOMO–LUMO
orbitals and electronic spectral contributions.
2.2
|
Synthesis of 9-hexyl-9H-carbazole-
3,6-dicarbaldehyde (1)
To a two-necked round-bottomed (RB) flask, 100 ml, 15 ml of stirred
solution of dry dimethyl formamide (DMF) at 0ꢀC was added and then
18 ml phosphorus oxychloride was added dropwise under argon
atmosphere until a coloured Vilsmeier salt completely precipitated.
Next, the 9-hexyl-9H-carbazole solution (1.00 g, 4 mmol) in 10 ml
DMF was added to a reaction mixture dropwise, while stirring at room
temperature. The reaction mixture was stirred overnight at room
3
|
RESULTS AND DISCUSSION
3.1
derivative
|
Synthesis and structural elucidation of CzPT
The synthetic pathway of a new carbazole-based thiazolidine-5-one
compound (CzPT) is illustrated in Scheme 1. The formylated

906
BAWAZEER ET AL.
SCHEME 1 Formation of CzPT derivative
N-hexyl-carbazole, 9-hexyl-9H-carbazole-3,6-dicarbaldehyde (1), was
obtained according the standard Vilsmeier–Hack reaction proto-
col.[31] Furthermore, ethyl-2-aceto-2-(5-oxo-3-phenylthiazolidin-
2-ylidene)acetate (2) was prepared with a 67% yield by nucleophilic
addition of ethyl acetoacetate to phenyl isothiocyanate in DMF and
KOH followed by in situ cyclization with chloroacetyl chloride as
previously described in the literature.[43] In the final step, the target
carbazole-based thiazolidine-5-one chromophore (CzPT) was
obtained with a 86% yield using a modified Knoevenagel reaction.
The reaction proceeded successfully by heating the precursor 1 with
thiazolidine-4-one derivative 2 in ethanol and piperidine. Targeted
organic dye was purified using recrystallization from ethanol. The
structure of the newly synthesized chromophore (CzPT) was
confirmed by various spectroscopic techniques. The IR spectra
showed absorptions at 1726 and 1684 cm−1 related to carbonyl
functions (C=O). The 1H NMR spectrum gave
a triplet at δ
0.81 ppm for three protons (CH3), multiplet at δ 1.07–1.12 ppm for
six protons (CH2CH2CH2), triplet at δ 1.21 ppm for six protons (two
CH3), multiple at δ 1.78 ppm for two protons (CH2), singlet at δ
2.37 ppm (two –COCH3), quartet at δ 4.21 ppm for four protons
(two –OCH2), and triplet at δ 4.51 for two protons (NCH2). The aro-
matic protons resonated as multiplet at δ 7.36–7.78 ppm, while ole-
finic protons resonated as singlet at δ 7.97 ppm (two C=CH). Mass
analysis displayed a molecular ion peak at m/z = 882.50 (with rela-
tive intensity, 16.65%) related to the molecular formula
C50H47N3O8S2.
FIGURE 1 Normalized UV–vis spectra of CzPT in different solvents (a) and linear fitting of absorbance-concentration plot (b)

BAWAZEER ET AL.
907
3.2
|
Absorption spectra and solvatochromism
used in absorption spectral measurements and the corresponding λmax
were recorded. The λmax data showed a red shift with increasing
polarity index from n-hexane to chloroform, 430 to 474 nm, respec-
tively (Table 1). Using solvents with a higher polarity index, namely
acetone and DMF, led to a blue shift, 465 and 468 nm, respectively.
The difference in the maximum energy (Emax) between the most polar
and nonpolar solvent, ΔEmax, was calculated to estimate the value and
sign of solvatochromism (Table 1). The calculated ΔEmax was +5.40 in
which the positive sign is evidence that probe had red shifted and the
CzPT ground state was less polar than the lowest excited state.[45]
The linear solvation-energy relationship (LSER) was applied to
explore CzPT solvatochromism behaviour according to the next
CzPT UV–vis spectra, 1 × 10−4 M solution in different solvents, pro-
duced two bands, a weak one at 396–400 nm and a strong one,
λmax = 429–474 nm. The first band was attributed to π–π* transitions
within conjugated aromatic moieties. While, the latter band was
assigned to intramolecular charge transfer (ICT) that has π–π* transi-
tion characteristics[41] which significantly enhanced its intensity
(Figure 1a). At λmax, the effect of CzPT solution concentration on
absorbance, in chloroform, was studied in the range 1 × 10−6
-
1 × 10−3 M. As shown in Figure 1b, absorbance increases reaching a
plateau at 1 × 10−4 M after which Beer's law was not applicable. The
linear fitting parameter exhibited a high molar extinction coefficient
(ε) 2.04 × 104 L mol−1 cm−1, obtained from the slope, with a good lin-
ear regression, r2 = 0.9649. This deviation from Beer's law may be
because the CzPT molecules underwent H-type aggregation. Such
promoted aggregation was established by increasing the concentra-
tion in solution.[42] In addition, the molar extinction coefficients (ε) in
different solvents ranged from 2.62 × 103 L mol−1 cm−1 in n-hexane
to 2.04 × 104 L mol−1 cm−1 in chloroform (Table 1). The obtained high
ε values endorsed the suggested π–π* characteristics of ICT transition
(λmax) that originated from enhanced delocalization of electrons.[41,43]
Transition band type affected the absorption coefficient value and
expression[46,47]
:
ðXYZÞs = ðXYZÞ0 + aα + bβ + cπꢁ
where (XYZ)S, (XYZ)0, α, β and π* denote solvent absorption λmax in
cm−1, constant, hydrogen bond donor (HBD) or acidity, hydrogen
bond acceptor (HBA) or basicity, and polarizability parameter based
on π–π* absorption of substituted aromatics,[48] respectively. The
coefficients a, b, and c are related coefficients for each polarity scale,
respectively.
Multilinear regression showed good regression (r2 = 0.9953) with
standard deviation (SD) 60.96. The values of absolute coefficients
indicated that solvent HBD property, α, is the most effective parame-
ter in λmax, a = 1781.08. While, the solvent polarizability parameter,
π*, and solvent HBA became the second and third orders, c and
b were 933.90 and 153.76, respectively (Table 2). Additionally, the
HBD coefficient value was ꢂ12 times greater than that of the HBA
coefficient. Therefore, the results clearly showed that multilinear
regression described the CzPT solvatochromism origin.
optical energy gap, Eg, which was determined by Tauc's equation[44]
:
r
ðαhνÞ = Bðhν−EgÞ
where B is the energy independent constant and the exponent r = ½, or
2, for direct or indirect conditions, respectively, and allowed transition
band. The graphical representation of (αhν)r vs. (hν), at different
r values, was used to estimate Eg by extrapolating the linear portion of
the curve to intercept the abscissa axis at r = 2. Therefore, the optical
band gap could being estimated and was found to be in the range of
2.84–2.66 eV (Table 1). This value was low enough to reflect the ease
of electronic transition between HOMO and LUMO levels. Therefore it
led to relocation of electrons and left a hole due to facilitated electronic
transitions. The values appeared to reflect the closeness of the optical
and electronic bands, which is preferable for optical properties.[45]
The molecule that exhibited solvatochromism was differentially
solvated in both ground and excited states. To explore the CzPT
derivative solvatochromism, solvents with diverse polarity index were
3.3
|
Fluorescence spectra
The CzPT fluorescence spectra in chloroform, concentration range
1 × 10−6 to 5 × 10−4 M, showed the effect of solution concentration on
both intensity and maximum wavelength (Figure 2). Increasing the solu-
tion concentration led to a red shift of λem along with an intensity
increase until it reached a maximum shift (10 nm) at 1 × 10−5 M concen-
tration. At higher concentrations, >1 × 10−5 M, the λem shifted to higher
TABLE 1 CzPT absorption λmax, extinction coefficient (ε), maximum energy (Emax) and absorption optical energy gap (Eg(Abs)) in different
solvents
Solvent
Hexane
CH2Cl2
CHCl3
Polar index
εr
1.88
μ (D)
0.08
1.14
1.14
2.7
λ
max (nm)
ε (mol−1 cm−1
2.62 × 103
1.69 × 104
1.87 × 104
1.14 × 104
1.05 × 104
)
Emax (kcal/mol)
66.49
Eg(Abs) (eV)
2.66
0.1
3.1
4.1
5.1
6.4
430
471
474
465
468
8.93
4.89
60.70
2.50
60.32
2.48
Acetone
DMF
20.56
36.71
61.49
2.48
3.81
61.09
2.50
εr dielectric constant and μ dipole moment.

908
BAWAZEER ET AL.
TABLE 2 The absorption and
fluorescence spectra multilinear
regression parameters
Absorption
Fluorescence
Parameter
Value
Standard error ( )
128.84
Value
Standard error ( )
249.53
Intercept
22111.01
−1781.08
153.76
−933.90
0.9953
60.96
3311.96
−4991.20
−500.89
−391.10
0.9707
α
976.37
1891.03
β
301.42
583.78
π*
r2
SD
105.36
204.06
118.07
FIGURE 3 Normalized fluorescence spectra of CzPT, 1 × 10−5 M,
FIGURE 2 Effect of CzPT concentration on the fluorescence
performance in chloroform
in different solvents
wavelengths but was accompanied by a dramatic decrease in intensity.
This behaviour may originate from excited molecules aggregating with
unexcited molecules to form differently excited complexes, excimer or
exciplex, which may or may not luminesce or luminesce at different fre-
quencies compared with the monomeric excited molecule. Additionally,
increasing the concentration led to a decrease in intermolecular mean
distance and consequently molecule excitation energy was transmitted
to adjacent molecules even as far as 100 nm.[42,49]
The fluorescence spectra of CzPT, 1 × 10−5 M, in solvents with
different polarity displayed one peak that affected by solvent polarity
(Figure 3). Stokes' shift, in cm−1, Δꢀν = ꢀνabs −ꢀνem , fundamentally origi-
nates from the structural relaxation of the molecular skeleton in the
excited state. In general, the calculated Stokes' shift (ΔꢀνÞ of CzPT
decreased with increasing polarity of the solvents, i.e. for less polar
hexane, Δꢀν = 3801 cm−1, while in DMF it was 2676 cm−1 (Table 3).
The Lippert–Mataga equation was applied to interpret the spec-
tral shifts of the CzPT derivative due to solvent molecule reor-
ientation that was described by the solvent orientation polarizability
light in vacuum, a is solvent cavity (Onsager cavity radius), εr is the
dielectric constant and n is the refractive index.
The Lippert–Mataga plot, Δꢀν versus Δf, exhibited poor linearity,
with a regression coefficient (r2) of 0.5087, neglecting n-hexane
(Figure 4a). This poor linear regression coefficient suggested that
Lippert–Mataga did not account for additional factors such as fluo-
rophore hydrogen bonding and ICT.[51]
To overcome Lippert–Mataga shortages, the LSER, as shown in
the following equation,[46,47] was employed to describe the CzPT–
solvent interaction and its effect on Stokes' shifts:
ðXYZÞs = ðXYZÞ0 + aα + bβ + cπꢁ
where (XYZ)S is the Stokes' shift, and other parameters (XYZ)0, α, β, π*,
a, b, and c[48] have been described before.
The solvent Stokes' shift showed a good regression coefficient
(r2 = 0.9707) compared with the Lippert–Mataga plots and the
obtained coefficients were displayed in Table 2. The coefficients abso-
lute value revealed that the Stokes' shifts were affected greatly by the
solvent hydrogen bond donating capability, HBD, or acidity in which
the HBA or basicity comes in the second position. Additionally, the
HBD coefficient absolute value, a, was ꢂ10 and was 13 times higher
parameter (Δf) and expressed by this equation[50]
:
À
Á
ꢀ
ꢁ
ꢀ
ꢁ
2 μe −μg
ϵr −1
2ϵr + 1
n2 −1
2n2 + 1
Δꢀν = ꢀνa −ꢀνf =
2 ðΔfÞ + constantΔf =
−
hca3
where Δꢀν is Stokes' shift (cm−1), μe is the excited state dipole, μg
is the ground state dipole, h is Planck's constant, c is the velocity of
than that of HBA and the dipolarity/polarizability,
b and c,
respectively.

BAWAZEER ET AL.
909
TABLE 3 CzPT maximum λem
,
Solvent
Hexane
CH2Cl2
CHCl3
Δf
α
β
π*
λ
em (nm)
Δꢀν (cm−1
3801
)
ϕf
Eg(em)
Stokes' shift (Δꢀν), emission optical energy
gap (Eg(em)), quantum yield (ϕf) and
solvents orientation polarizability (Δf)
−0.0014
0.2171
0.1504
0.2841
0.2744
0
0
−1.23
0.73
0.69
0.62
0.88
528
535
522
528
522
0.728
0.776
0.825
0.662
0.628
2.41
2.35
2.36
2.38
2.32
0.13
0.2
0.08
0
0.1
0.1
0.48
0.69
2292
2049
Acetone
DMF
2348
2676
FIGURE 4 (a) Lippert–Mataga plot of Δꢀν vs. Δf; (b) linear relationship between experimental and predicted Δꢀν of CzPT
To examine LSER quality, the predicted Stokes' shifts, obtained
using the estimated parameters from LSER, were correlated graphi-
cally to the experimental values as displayed in Figure 4b. A good
linear relationship was obtained that had slope and regression
coefficient values almost at unity, with slope 0.9927 and
r2 = 0.9902, respectively. Therefore, the solvatochromic origin of
=
FIGURE 5 The CzPT optimized
structure in hexane (H atoms were hidden
for clarity)

910
BAWAZEER ET AL.
the CzPT derivative was explained using the multilinear regression
model.
decreased in highly polar solvents to reach 0.628 in DMF, the most
polar solvent.
Finally, CzPT relative quantum yield (ϕ) in different solvents was
assessed by quinine sulfate in 0.1 M H2SO4 as standard.[52] As shown
in Table 3, quantum yield increased when increasing the solvent polar-
ity and reached a maximum in CHCl3 of 0.825, after which it
3.4
|
Computational aspects
3.4.1
|
Quantum chemical studies
The CzPT derivative was optimized in the gaseous state and then in
hexane and DMF as solvent to study the solvent effect using DFT
quantum chemical calculations. In gaseous and solvated states, the
CzPT optimized structures have almost planar configuration in which
the carbazole and thiazolidinone moieties were co-planar. Both phenyl
rings and oxobutanoate groups were perpendicular and tilted with
respect to the carbazole plane, respectively (Figure 5). Complete lists
of DFT obtained bond length, bond angle and dihedral angles are
shown in Tables S1–S3.
Frontier molecular orbitals, HOMO and LUMO, have noteworthy
roles in understanding ICT.[53–55] HOMO revealed the electron dona-
tion ability, which appeared to spread over electron-rich moieties,
while LUMO presented electron acceptability, which appeared local-
ized on electron-deficient moieties.[56] The gaseous and solvated fron-
tier orbitals 3D-plots demonstrated HOMO were concentrated mainly
on π-orbitals of carbazole and heteroatoms of thiazolidinone and
oxobutanoate groups, while LUMO were concentred on π*-orbitals of
these moieties. The red and green colours were designated as wave
function positive and negative phases[57] (Figure 6).
In the gaseous state, EHOMO and ELUMO were −5.63 and
−4.03 eV, respectively, with an exhibited energy gap of ΔEH-
= 1.60 eV. In the solvated state, hexane solvation led to a slight
L
decrease in both EHOMO and ELUMO, by 0.03 eV and so the energy gap
was maintained at 1.60 eV. In contrast, DMF solvation led to an
increase in EHOMO and ELUMO, with respect to the gaseous state, and
were −5.72 and −4.15 eV, respectively, but ΔEH-L was slightly
FIGURE 6 Frontier HOMO and LUMO of CzPT in gaseous state
FIGURE 7 TD-DFT electronic spectra of
CzPT in hexane and DMF

BAWAZEER ET AL.
911
changed (1.58 eV). Hexane slightly stabilized both molecular orbitals,
while DMF de-stabilized both, which may suggest that HOMO and
LUMO have almost the same degree of polarity.
tions did not account for the effect of spin-orbit coupling and molecu-
lar vibrational motion.[58,59]
The generated TD-DFT electronic spectra of CzPT in hexane and
DMF showed one band at 515 and 520 nm, respectively (Figure 7).
The DFT calculated band resulted from the overlapping of many tran-
sitions, as shown in Table 4. The data indicated transitions at 525 and
537 nm in hexane and DMF, respectively, which mainly originated
from HOMO!LUMO transitions with highest oscillator strength,
0.578 and 0.556, and contribution, 83% and 91%, respectively. More-
over, the molecular orbitals HOMO, HOMO-1, and HOMO-2 were
the donors, while only LUMO and LUMO+1 were the acceptors in
other electronic transitions at long or shorter wavelengths. Finally, the
comparison of experimental data with TD-DFT electronic spectra, rev-
ealed the presence of a calculated λmax band at higher wavelengths
than the experimental, which may be because the TD-DFT calcula-
3.4.2
|
Crystal shape effect
Hirshfeld demonstrated a procedure to put the closest model of a crys-
tal inside a crystal packing system using Crystal explorer software
3.1.[60] The CzPT derivative was adjusted using the VESTA package to
be suitable for crystal building.[61] A 3D-model of the compound was
optimized first and the crystal was established through normalized con-
tact distance (dnorm) and curvedness types (Figure 7). The model of
dnorm type differentiates the contact features between molecular sur-
faces in crystal packing by colour indicators. Red, white, and blue col-
ours, refer to strong, moderate, and weak interactions, respectively.
The strength of contact depends on the length of H-bonding between
surfaces, according to van der Waals radii. The short distance depicted
by red spot points to strong contact, while blue and white point to long
and moderate lengths, respectively. Several red spots surround oxygen
atoms and reflect the significant role of oxygen atoms in contact prefer-
ences between neighbouring crystals inside packing. Furthermore, the
curvedness type divided the surface into several portions suitable for
contact. Side chains may prevent perfect contact between the closest
crystals and packing may be yielded with many imperfections.[62] It is
known that the crystal features and geometry of a compound deter-
mine its physicochemical properties, particularly its photophysical
properties during electron transfer processes.[63] The unit cell was dem-
onstrated via the VESTA package to visualize the most fitted shape of
unit cell that seemed to be a face-centred cubic shape (Figure 8). The
volume of the unit cell was 15 059.2 Å, a = b = c = 24.6945 Å and
α = β = γ = 90o. In addition, the X-ray diffraction (XRD) pattern was
obtained using Crystal Maker software (Figure 9) to determine
d-spacing (0.10 Å) and particle size (24.69 Å). Small d-spacing between
the inner levels in the crystal, may lead to subsequent emission of light
at a lower energy levels and causes photophysical properties. Also, the
reduced uniformity of the crystal feature may lead to dislocation or
anomalous arrangement of crystals with irregular spacing, which
automatically enhance the optical properties of such crystals.
TABLE 4 TD-DFT absorption electronic transitions of CzPT in
hexane and DMF
Transition
(nm)
Osc.
strength
Major contributions
Hexane
551
0.046
0.232
HOMO-2!LUMO (96%)
536
HOMO-2!LUMO+1 (78%), HOMO-
1!LUMO+1 (19%)
525
507
0.578
0.338
HOMO!LUMO (83%)
HOMO-1!LUMO (43%),
HOMO!LUMO+1 (43%)
DMF
537
515
511
0.556
0.171
0.049
HOMO!LUMO (91%)
HOMO-1!LUMO+1 (82%)
HOMO-2!LUMO+1 (27%), HOMO-
1!LUMO (32%), HOMO!LUMO
+1 (31%)
508
0.453
HOMO-1!LUMO (49%),
HOMO!LUMO+1 (51%)
FIGURE 8 dnorm (a), curvedness (b) and unit cell (c) of CzPT compound

912
BAWAZEER ET AL.
FIGURE 9 Theoretical XRD
pattern of CzPT compound
4
|
CONCLUSION
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A new chromophore, 3,6-bis (thiazolidin-5-one-2-yl)carbazole (CzPT)
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hexylcarbazole
with
2
moles
of
ethyl-2-aceto-2-(5-oxo-
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How to cite this article: Bawazeer TM, Althagafi I, Morad M,
et al. Luminescence feature of new 3,6-di(thiazolidin-5-one-2-
yl)-carbazole derivative: synthesis, photophysical properties,
density functional theory studies, and crystal shape effect.
Luminescence. 2021;36:904–913. https://doi.org/10.1002/
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