Highly fluorescent aryl-cyclopentadienyl ligands and their tetra-nuclear mixed metallic potassium-dysprosium clusters

Article abstract of DOI:10.1039/d0ra05316c

Two alkyl substituted triaryl-cyclopentadienyl ligands [4,4′-(4-phenylcyclopenta-1,3-diene-1,2-diyl)bis(methylbenzene) (1) and 4,4′,4′′-(cyclopenta-1,3-diene-1,2,4-triyl)tris(methylbenzene) (2)] have been synthesized via cross-aldol condensation followed

Full text of DOI:10.1039/d0ra05316c

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Highly fluorescent aryl-cyclopentadienyl ligands
and their tetra-nuclear mixed metallic potassium–
dysprosium clusters†
Cite this: RSC Adv., 2020, 10, 39366
Selvakumar Arumugam, ‡a Pulikanti Guruprasad Reddy, ‡b Maria Francis,b
b
b
a
*
*
Aditya Kulkarni,
Sudipta Roy
and Kartik Chandra Mondal
Two alkyl substituted triaryl-cyclopentadienyl ligands [4,40-(4-phenylcyclopenta-1,3-diene-1,2-diyl)
bis(methylbenzene) (1) and 4,40,400-(cyclopenta-1,3-diene-1,2,4-triyl)tris(methylbenzene) (2)] have been
synthesized via cross-aldol condensation followed by Zn-dust mediated cyclization and acid catalyzed
dehydration reactions. The fluorescence properties of 1 and 2 have been studied in solution and solid
state. The ligands exhibited aggregation-induced emission enhancement (AIEE) in THF/water solution. 1
and 2 have been found to be significantly more fluorescent in the solid state than in their respective
solutions. This phenomenon can be attributed to the strong intermolecular CH/p interactions present
in 1 and 2 which leads to the tight packing of molecules in their solid-state. Both 1, 2 and their
corresponding anions have been studied by theoretical calculations. Ligands 1 and 2 have been shown to
react with anhydrous DyCl3 in the presence of potassium metal at high temperature to afford two
Received 17th June 2020
Accepted 8th October 2020
DOI: 10.1039/d0ra05316c
fluorescent
chloride-bridged
tetra-nuclear
mixed
potassium–dysprosium
metallocenes
rsc.li/rsc-advances
[(Me2Cp)4Dy2IIICl4K2]$3.5(C7H8) (5) and [(Me3Cp)4Dy2IIICl4K2]$3(C7H8) (6), respectively in good yields.
et al., respectively.8,9 However, the main mechanism behind the
AIEE phenomenon is the restriction of the intramolecular
rotation (RIR) in propeller-shaped molecules. RIR has helped to
block the nonradiative pathways resulting in enhanced emis-
sion response in the solid and aggregated states. AIEE has
opened a new channel towards the blooming of novel and
versatile organic luminescent molecules with high emission
efficiency and uorescence quantum yields. A few examples of
AIEE active molecules reported are: aromatic silole derivatives,10
tetraphenylethenes,11 diphenyldi-benzofulvenes,12 pyrene,13 and
thiophene derivatives.14 Thus, AIEE active organic materials are
highly essential for luminescent devices such as OLEDs and
also for other applications in material sciences. Moreover,
designing of blue-emitting organic uorophores has particu-
larly remained to be a challenge because of their low emis-
sion efficiency and poor stability as compared to red and
green-uorophores reported for their outstanding perfor-
mance.15 A few traditional blue-emitting molecules reported
in the literature are anthracene,16 uorene,17 pyrene deriva-
tives,18 and triphenylamine derivatives.19 However, these
molecules largely suffer from the ACQ effect in the aggre-
gated states owing to their planar structures. Subsequently,
the alternative polyaryl cyclopentadiene (Cp)-derivatives, viz.,
1,2,3,4-tetraphenyl-1,3-cyclopentadiene (TPC) and 1,2,3,4,5-
pentaphenyl-1,3-cyclopentadiene (PPCp) have been devel-
oped as functional propeller-shaped molecules.20 Addition-
ally, their utility has been explored in electroluminescent
devices as blue light-emitting layers.20b–f As a part of the
Introduction
The development of stable and p-conjugated organic lumines-
cent materials has received signicant interest for both funda-
mental research and practical applications due to their
potential use as organic light-emitting diodes (OLEDs),1 bio-
logical probes,2 organic solid state lasers,3 uorescent sensors,4
photonic devices,5 and at panel displays and in illumination.6
Most of the reported organic luminescent materials are highly
emissive in dilute solutions and poorly/non-emitting in the
solid state/neat thin solid lms due to the aggregation caused
quenching (ACQ) effect resulting in their unsatisfactory appli-
cations in optoelectronic devices such as OLEDs and lasers.7 In
this context, it is noteworthy to mention that to overcome the
problems associated with ACQ, two interesting photo-
luminescence concepts, i.e., “Aggregation Induced Emission
(AIE)”, and “Aggregation Induced Emission Enhancement
(AIEE)” have been subsequently reported by Tang et al. and Park
aDepartment of Chemistry, Indian Institute of Technology Madras, Chennai 600036,
India. E-mail: csdkartik@iitm.ac.in
bDepartment of Chemistry, Indian Institute of Science Education and Research (IISER),
Tirupati 517507, India. E-mail: roy.sudipta@iisertirupati.ac.in
† Electronic supplementary information (ESI) available: Single crystal X-ray
structures of 1, 2, 5, 6, NMR spectroscopic data, and computational details.
CCDC 2006636, 2006639 for compounds 1, 2; 2006659, 2007965 for complexes
5, 6, respectively. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/d0ra05316c
‡ SA and PGPR contributed equally to this work.
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continuous efforts21–23 in nding the blue-emitting organic
uorophores, Ning et al.22 developed a series of triaryl
substituted Cp ligands with improved photoluminescence
(PL) and high quantum yields.
Apart from their excellent photophysical properties that they
exhibit the Cp ligands are well established for the synthesis of
one of the very important class of organometallic complexes,
known as the sandwich complexes or the metallocenes.24 Since
the discovery of ferrocene,25 the quest for developing new
synthetic routes for novel sandwich complexes are on great
demand because of their potential applications in catalysis,
medicinal-, electro-chemistry, and as fuel additives.26 In this
regard, syntheses of lanthanide-based sandwich complexes27
are noteworthy in recent times, especially because of their
applications as single molecule magnets (SMMs) and single ion
magnets (SIMs).28,29 Herein, we report the syntheses of two new
(AIEE active and blue light emitting) triaryl Cp ligands (Me2Cp–
H) (1) [Me2Cp–H ¼ 4,40-(4-phenylcyclopenta-1,3-diene-1,2-diyl)
Scheme 1 Synthetic routes for 4,40-(4-phenylcyclopenta-1,3-diene-
1,2-diyl)bis(methylbenzene) (1), 4,40,400-(cyclopenta-1,3-diene-1,2,4-
triyl)tris(methylbenzene) (2) and their potassium salts 3, 4.
bis(methylbenzene)], (Me3Cp–H) (2) [Me3Cp–H
¼
4,40,400-
(cyclopenta-1,3-diene-1,2,4-triyl)tris(methylbenzene)] and their
photophysical properties in solution, solid state and as aggre-
gates. Finally, 1 and 2 have been shown to afford the two novel
chloride bridged, tetra-nuclear, mixed potassium–dysprosium
sandwich complexes [(Me2Cp)4Dy2IIICl4K2]$3.5(C7H8) (5) and
[(Me3Cp)4Dy2IIICl4K2]$3(C7H8) (6), respectively in very good
yields.
uorescence spectra of 1 and 2 in DCM shows emission at
455 nm and 470 nm, respectively when excited at 359 nm
(Fig. 1a).
The solid-state photoluminescence (PL) spectra of 1 and 2
display emissions at 466 nm and 480 nm, respectively (Fig. 1b).
Moreover, 1 and 2 illuminate bright green-blue light in their
solid-state upon irradiation with UV-365 nm light as shown in
Fig. 2a. It is worth mentioning that the solid state absorption
and emissions of compounds 1–2 are red-shied with higher
intensity than those observed in solution state PL spectra,
attributing to their solid state packing (Fig. 2b), leading to AIEE
property2,8 (see ESI†). Interestingly, the emission spectra of 1
and 2 in different solvents are inuenced by the nature of the
solvent polarity.22c Emissions with higher intensities were
noticed in non-polar, non-coordinating solvents (n-hexane,
toluene) than those in polar, coordinating (MeCN, THF, Me2CO,
MeOH, EtOH) and polar, non-coordinating (DCM, CHCl3)
Results and discussion
The triaryl substituted cyclopentadienyl ligands 1 and 2 were
synthesized in a three-step synthetic process. Initially, the 1,5-
di-keto compounds (1a, 1b) were synthesized through cross-
aldol condensation between the corresponding aromatic alde-
hyde and acetophenone derivatives in the presence of sodium
hydroxide as a base. Next, the 1,2-diol compounds (2a, 2b) were
obtained by the reductive cyclization of the corresponding 1,5-
di-keto compounds (1a, 1b) in presence of Zn-dust/acetic acid
mixture at 90–100 C.22 Finally, the targeted triaryl substituted
ꢀ
Cp compounds (Me2Cp–H) (1) and (Me3Cp–H) (2) were obtained
by the dehydration of the corresponding 1,2-diol compounds
(2a, 2b) in presence of ethanol and hydrochloric acid under
reux conditions (Scheme 1, see ESI† for details).
Compounds 1 and 2 are thoroughly characterized by IR,
NMR, and mass spectrometric analysis (see ESI†). The molec-
ular structures of 1 and 2 are determined by single-crystal X-ray
diffraction studies. Aer successful syntheses and character-
ization of 1 and 2, we have investigated their photophysical
properties in solution (Fig. 1) as well as in solid state using UV-
visible (Fig. 1b), diffuse reectance spectroscopy (DRS), and
photoluminescence (PL) spectroscopic techniques. Fig. 1a
shows UV-visible absorption and emission spectra of 1 and 2 in
DCM, where both of these compounds display absorption at
359 nm (HOMO to LUMO). The p–p* transitions of the conju-
gated aromatic phenyl moieties (see ESI† for TD-DFT calcula-
tions) and core Cp units in 1 and 2 (DELUMO–HOMO ¼ 5.32 (1),
Fig. 1 (a) UV-visible absorption (left) and emission spectra (right) of 1
and 2 in DCM; (b) solid-state DRS-UV (left) and emission spectra (right)
of 1 and 2; (c) PL spectra of 1 (left); (d) PL spectra of 2 (right) in different
5.29 (2) eV) are responsible for this absorption. The solvents.
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times higher in the solid state (2.25 ns (1), 1.6 ns (2)) than those
in solutions (0.3 ns (1), 0.2 ns (2)) (Fig. S2†). The quantum yields
of 1 and 2 are found to be 4.5% and 10.3%, respectively in
toluene (see ESI†).22
Moreover, a detailed AIEE studies of 1–2 were investigated in
THF : water or acetone : water mixture by sequential addition of
different fractions of water into THF or acetone. According to
our ndings, compounds 1 and 2 exhibited highest uores-
cence emissions when the fractions of water were 60%
(acetone : water mixture, see ESI†) and 80% (THF : water
mixtures, Fig. 3), respectively. The increase of uorescence
intensity can be attributed to the AIEE effect caused by the
formation of molecular nano-aggregates in the miscible solvent
pair, which can restrict the intermolecular rotations of mole-
cules resulting in increased uorescence emission.8,22
The detailed AIEE investigations of these compounds are
described in ESI.† In addition, to understand the mechanism
for orescence emission of compounds 1 and 2 in the solid or
aggregated states, we have investigated the relationship
between their structure and photophysical properties. The
molecular structures of compounds 1 and 2 adopt non-coplanar
geometry and possess different packing patterns in the crystal
lattice as shown in Fig. 4 (top) (also see Fig. S10–S14, ESI†).
Briey, due to strong C–H/p interactions exerted between the
molecules of 1 or 2 can led to 1D J-type molecular aggregation of
molecular columns in the crystal lattice (Fig. 2, middle), this
means intermolecular motions are not free between the mole-
cules hence enhanced PL intensity observed (for detailed
mechanistic ESI†).
Fig. 2 Ligand 1 with UV light (365 nm (a)) and its packing along 1D
chain (top, left). Ligand 2 with UV light (365 nm (b)) and its packing
along 1D chain (top, right). Intermolecular C–HCp/pCp interactions
(middle) shown in space filling model along 1D chain leading to much
brighter emission of 2 than that of 1. Molecular electrostatic potential
(MEP) surfaces of two interacting neighbouring molecules of 1
(bottom, left) and 2 (bottom, right).
The contour plots of the Laplacian for ligands 1–2 are shown
in Fig. 4, (bottom). The electron density greater than 0.2,
negative Laplacian V2r(r) and negative H(r) (Table S5†) at the
bond critical point indicate an electron sharing covalent bond
between Cp and the phenyl rings. The Bader charge on phenyl
ring is slightly positive (+0.007), indicating a possible very weak
charge transfer from Cp-ring to phenyl ring of 1–2. The contour
plots show charge accumulation near to the C-atoms in both Cp
and phenyl rings supporting the electron sharing interactions
(Fig. 4, bottom). The extracted parameters (Table S5†) of each
molecule of 1–2 are very similar, suggeting that the differences
in their luminescence properties are solely due to their differ-
ences in the molecular packing in solid state (Fig. 2, also see
ESI† for detailed structure descriptions (1–2) and correlation).
Aer completing the PL studies of 1 and 2, we explored their
applicability as the stabilizing ligands for the syntheses of rare
solvents. For example, the emission of 1 in n-hexane and
toluene are slightly red-shied with high intensity when
compared to the emission in polar solvents (Fig. 1c). Likewise,
the similar trend was noticed for 2, but the emission in n-
hexane is slightly blue-shied with higher intensity than in
toluene (Fig. 1d). Moreover, the quenching of uorescence
activity was noticed for both the compounds 1–2 in polar
solvents like, DCM, acetone and methanol as shown in Fig. 1c
and d (also see ESI, Fig. S6†). This is probably due to the
unchanged singlet excited state of 1 and reduced non-emissive
decay with decreasing solvent polarity (Fig. S6†).22c,29 In polar,
coordinating solvents (MeOH, EtOH, MeCN, THF, Me2CO)
(Fig. S4–S6†) the electrons in the excited states of molecules can
undergo relaxation via radiative processes due to the possible
Cp–H/solvent interactions (donor atom of solvent interacting
with acidic Cp–H of ligands 1–2, see ESI†), leading to the
observed decrease in PL intensity. In case of non-polar, non-
coordinating solvents, like toluene and n-hexane; such solvent
interactions with MenCp–H (1, 2) are not observed leading to
high PL intensity. The AIEE properties of 1 and 2 were studied in
acetone/water and THF/water mixtures which were further
correlated with their respective solid state structures and 3D
molecular packing diagrams (see ESI† for details).
The uorescence lifetimes of 1–2 were measured both in
solution- and solid states which were found to be nearly 7–8
Fig. 3 Fluorescence spectra of (a) 1 and (b) 2 in water/THF mixture
with the increases of the water fractions, starting from 10–90%.
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Fig. 5 HOMO and LUMO of Me2Cp–H (1) (a and b) and Me2Cpꢁ anion
(c and d) calculated at M06-GD3/def2TZVP level of theory (in gas
phase). Energies are in eV.
towards moisture and air, hence stored under inert atmosphere.
The disappearance of the Cp–H resonances for KCp salts in the
1H-NMR spectra was indicative of the formation of the 6p
electronic aromatic Cp core.
NBO analysis (Fig. 5) of Me2Cpꢁ at M06-GD3/def2TZVP level
of theory indicates that the HOMO consists of the p-cloud
(Fig. 5c) in the central Cp-core and the phenyl rings, while the
LUMO is composed of vacant p* orbitals (Fig. 5d). The NBO
analysis indicates covalent C–C s-bonds with high occupancy
(1.96–1.97) for all ve C–C bonds of the Cp-core, with WBI
(Wiberg Bond Indices) values ranging from 1.22–1.41, indicating
partial double bond character consistent with the aromaticity.
The C–C double bonds carry a low occupation of 1.70–1.77e. The
NBO analysis also indicates the existence of highly conjugated
p-cloud in the central Cp-core in both the Cpꢁ anions (see ESI†).
The energies of HOMO and LUMO of the anions (MenCpꢁ)
are higher than those of their corresponding protonated neutral
analogues (1–2). Moreover, the HOMO–LUMO energy gaps of
the anions are found to be smaller than those of their neutral
analogues (1–2) (Table S7†).
Fig. 4 Molecular structures of 1–2 (top); color codes: carbon: grey;
hydrogen: yellow. Laplacian contour plots of ligands 1–2 (bottom).
earth,31 Dy(III)-based sandwich24–27 complexes. Initially, we con-
verted 1 and 2 into their corresponding potassium cyclo-
pentadienyl salts, (Me2Cp)K(THF) (3) and (Me3Cp)K(THF) (4) by
separately reacting 1 and 2 with K-metal (1.2 equiv) for 24 h in
THF at room temperature (Scheme 1). In case of complex 3, the
color of the reaction mixture changed from yellow to dark blue
upon reaction completion as indicated by the complete
consumption of the metallic potassium. This might be due to
the possible, facile charge transfer from the central anionic-Cp
ring to the adjacent phenyl ring of 3, leading to a quinone like
bonding situation (partial CPh–CCp double bond) in certain
rotamers of 3. Free rotation of phenyl ring around CPh–CCp
bond can increase the delocalization of electron densities with
a lower HOMO–LUMO energy gap of 3 producing a blue color.
Such delocalization might have reduced in the most stable
rotational conformation of 3, leading to the light-yellow color.
Another possibility is that the reaction of 1 with potassium
metal proceeds via a radical intermediate affording the potas-
sium salt 3.
Me2Cp–H (1) was further optimized in singlet diradical
excited state (1*), which is 3.06 eV (70.6 kcal molꢁ1) higher in
energy than its closed shell singlet ground state. This difference
in energy is very close to the energy of the photon (ꢂ360 nm,
Fig. 1) required to excite 1 / 1*. The a-SOMO and b-SOMO of
1* are given in Fig. 6.
The reaction between (MenCp)K(THF) salts (3–4) and anhy-
drous DyCl3 either in toluene or THF at high temperature in
The ltration of the blue reaction mixture, followed by
removal of THF under high vacuum yielded 3 as a pale-yellow
solid. In contrast, 2 did not show any color change of the
reaction mixture. Instead, the formation of yellow precipitate
was observed aer 24 h. The pure, yellow solid of 4 was obtained
upon ltration, followed by the subsequent drying under high
vacuum. These KCp salts (3–4) are found to be highly sensitive
Fig. 6 a- and b-SOMO of Me2Cp–H (1*) singlet biradical state (in gas
phase) calculated at UM062x(GD3)/Def2TZVPP//BP86(GD3)/Def2TZVPP
level of theory.
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˚
and 1.43 A) and other two m-bridged Cl-atoms (Cl4, Cl2) above
+
(1.76 and 1.80 A) the Dy2K2-plane (Fig. 7). Two K and Dy3+ ions
˚
occupy the body and wing positions, respectively. Each K+ ion is
centered between two phenyl rings showing h6 coordination
˚
with K–C distance in the range of 3.0729(12)–3.502(3) A. On the
hand, each Dy3+ ion is sandwiched between two cyclo-
pentadienyl rings showing h5 coordination with Dy–C distances
˚
in the range of 2.644(3)–2.768(3) A. This adopts a bent metal-
locene structure with the corresponding angles (Cp–Dy–Cp
centroid) in the range of 129.73–130.85ꢀ (5). These bending
angles are signicantly lower than those in the previously re-
ported neutral [(Cpttt)2DyCl] (147.59ꢀ)28b and cationic complexes
Scheme 2 Syntheses of complexes [(Me2Cp)4Dy2IIICl4K2]$3.5(C7H8)
(5) and [(Me3Cp)4Dy2IIICl4K2]$3(C7H8) (6).
[Dy(Cp*)2{m-(Ph)2BPh2}]
(152.56(7)ꢀ)28d
and
(134.00ꢀ),28g
[Dy(Cpttt)2][B(C6F5)4]
(BC6F5)4]
a pressure tube at 110 ꢀC does not lead to the isolation of
desired MenCp-containing Dy-complexes. However, the one pot
synthetic approach became successful (Scheme 2). A 1 : 2 : 2
molar mixture ꢀof anhydrous DyCl3, MenCp–H and K-metal in
toluene at 110 C stirred for two days under argon atmosphere
leading to the formation of light-yellow turbid reaction mixture.
Upon ltration of the reaction mixture, the clear ltrate was
concentrated and stored at room temperature for 4 days to
produce the light yellow blocks of [(Me2Cp)4Dy2IIICl4K2]$
3.5(C7H8) (5) or [(Me3Cp)4Dy2IIICl4K2]$3(C7H8) (6) in 71–72%
yields, respectively. The molecular structures of complexes 5
and 6 were determined by X-ray single crystal diffraction at 200
K. The structure renement and selected bond parameters for
complexes 5 and 6 are given in the ESI.†
[(h5-CpiPr5)Dy(h5-Cp*)
(162.507(1)ꢀ).28c In addition, the Dy–Cpcen distances in 5 vary in
˚
the range of 2.391–2.423 A which is very close to that of
ttt
28b
˚
[(Cp )2DyCl] (2.413 A) and greater than that of the corre-
ttt
+
28b
˚
sponding cationic complex [(Cp )2Dy] (2.309–2.324 A).
The Arcen1/K/Arcen2 (Ar ¼ 4-methylphenyl unit) angles are
found to be in the range of 113.97–116.84ꢀ (5–6). The K/K and
˚
˚
Dy/Dy distances in the K2Cl4Dy2 core are 4.363 A and 8.233 A,
respectively. Moreover, the Dy–Cl and K–Cl bond distances in 5
˚
are in the range of 2.5903(8)–2.6185(12) A and 3.0279(12)–
˚
3.4657(12) A, respectively.
It is to be noted that the Dy–Cl distances reported here fall in
the similar range of those reported previously in the complex,
ttt
28b
˚
[Dy(Cp )2Cl] (2.5400(13) A). The weak C–H/p interactions
exerted between the molecules of 5 led to the supramolecular
2D network in the crystal lattice (see ESI†).
Structural description of complex 5
The UV/vis spectrum of 5, recorded in acetonitrile (MeCN)
solution shows three absorption maxima at 232, 262 and
354 nm. The excitations of MeCN solution of 5 at 262, 320 and
354 nm lead to the ligand-centered emissions in the visible
range (426 nm) of spectrum (Fig. 9). The emission band of 5 is
blue shied by 30 nm when it is compared with that of neutral
ligand 1. The quantum yield of complex 5 is 0.8% in MeCN
solution which is approximately six times lower than that of its
neutral ligand (Me2Cp–H, 1), suggesting the signicant
quenching of uorescence emission in 5. The UV/vis/NIR
measurement of complex 5 in the range of 200–2000 nm did
not show absorption bands other than those seen in the UV/vis
region (262, 320 and 354 nm).
Complexes 5 and 6 are iso-structural; hence, only the structure
of 5 (Fig. 7) is described here (see ESI† for molecular structure of
6). Complex [(Me2Cp)4Dy2IIICl4K2]$3.5(C7H8) (5) crystallizes in
ꢀ
triclinic P1 space group. It possesses a buttery like Dy2K2Cl4
core (Fig. 8) with two m3-bridged Cl-atoms (Cl3, Cl1) below (1.02
Fig. 7 Molecular structure of 5; the hydrogen atoms are omitted for
the clarity. Selected bond lengths (A˚) and bond angles (ꢀ) are as follows:
Cl1–Dy2 2.6185(8), Cl2–Dy2 2.5874(8), Cl3–Dy1 2.5993(8), Cl4–Dy1
2.5903(8); Cl1–K2 3.0279 (12), Cl1–K1 3.0559(11), Cl2–K1 3.1805(11),
Cl3–K1 3.1404(12); Dy2–Cl1–K2 129.24 (3), Dy2–Cl1–K1 97.95 (3), K2– Fig. 8 Non planar Dy2K2Cl4 core along with chelating aromatic units
Cl1–K1 91.61 (3).
of complex 5.
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shown that the ligands 1 and 2 could be effectively utilized to
obtain the novel chloride bridged, mixed-metallic tetra-nuclear
potassium–dysprosium sandwich complexes (5–6). The metal (K
and K/Dy) complexes (4–5) display uorescence emission in the
visible region of the wavelength. Utilization of these complexes
as precursors for the lower coordinate Dy-cations are underway.
Conflicts of interest
There are no conicts to declare.
Acknowledgements
Fig. 9 UV/vis absorption (green line) and emission (blue, orange and
red lines when excited at 262, 320 and 354 nm, respectively) spectra of
complex 5 in MeCN solution.
SR and KCM gratefully acknowledge SERB, New Delhi for their
individual ECR grants (ECR/2016/000733 for SR; ECR/2016/
000890 for KCM). SA, MF thank CSIR for SRF and JRF, respec-
tively. PGR thanks IISER Tirupati for Postdoctoral Fellowship.
AK thanks KYPY for nancial support.
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In conclusion, two alkyl-substituted triaryl-cyclopentadiene
derivatives 1 and 2 have been synthesized and shown to
display captivating uorescence glow in the solid state upon
irradiation with UV-lamp. The central ve membered ring to
ring direct electrostatic interaction along the 1D-chain has been
found to be crucial for exhibiting a better uorescence property
by 2 than 1. Theoretical calculations and structure–property 10 L. Chen, Y. Jiang, H. Nie, P. Lu, H. H. Y. Sung, I. D. Williams,
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