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ChemComm
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HOMO(-4.77eV)LUMO(-1.20eV) energy gap(3.56eV) corresponds in their spiro ring-opened conformation. On a comparison to
DOI: 10.1039/D0CC03985C
to an absorption transition at 347nm in 2. The estimated absorption phosphorylation at hydroxyl- or amino- nucleophilic centres on
transitions in both 1 and 2 are in good agreement with the the substituents attached, the phosphorylation on xanthene
observed experimental absorption peaks (±25 nm). Absence of any based signalling subunit endorses the methodology of probe
HOMO → LUMO transition in the 400–600 nm region in the design for DCP detection on rhodamine platform.
elucidated structures of 1 and 2 also inferred to their existence of
rhodamine’s spirocyclic conformation. In the diethyl phosphate
appended 1 (1-DP), the energy of HOMO (-4.60eV) was found to be
Conflicts of interest
slightly increased and that of LUMO (-1.73 eV) was more stabilized
in comparison to those corresponding in 1, due to enhanced
conjugation in its ring-opened conformation in 1-DP adduct. As a
result, the HOMO-LUMO energy gap(2.86 eV) in 1-DP adduct
corresponds to a red-shifted absorption transition at 433nm. The
formation of diethyl phosphate derivative of ring-opened 1 was
evidenced from the spectroscopic evidences. It is assumed that the
reaction of 1 as Lewis base with DCP as Lewis acid undergoes
reorganization prior to formation of the 1-DP adduct where the P-O
bond formation compensate highly their combined reorganization
energies. The stability of newly formed P-O bond in 1-DP depends
predominantly on interacting parameters of the two involved
reactants, 1 and DCP. The stabilized energy of formation in the
energy-minimized structure calculation of 1-DP ascertained that as
well. In this context, the chemical potential and HOMO-LUMO
energy gap of the interacting molecules may be taken as the index
of chemical reactivity and subsequent stability of adduct formed. A
correlation of various parameters observed(ESI) for 1 and the
analytes, despite presumed to follow a pre-organizational approach
prior to react for a new adduct formation, predicted reaction
preferences of 1 towards DCP. (a)The HOMO-LUMO energy gap in
DCP(8.06eV) was observed to be higher than that of other analytes
where as that of 1(3.49eV) was lower in comparison to all analytes
studied. (b) The difference in calculated chemical potentials
between 1(3.04 eV) and DCP(4.29 eV) was found to be higher than
those in cases of other analytes. (c) The ground state dipole
moment (g) was estimated to be higher in DCP(4.64D) than other
analytes and lower than that in 1(4.98D), which correlates to a
higher affinity of DCP for adduct formation representing through a
lower difference in g between 1 and DCP over that between 1 and
other analytes. (d) The Mulliken charge over P-atom in
DCP(1.1811e) was calculated to be higher than that over P-atoms in
other organophosphate analytes, in correlation to the charge over
spiro-cyclic carbonyl O-atom(-0.5789e) in 1. Although a detailed
investigation would verify these observations for a comprehension
of reaction mechanism and despite the fact that mechanistic
behaviors of the molecules explained with the gas phase theoretical
calculations would diverge with the processes in solutions, the
preliminary correlations support the probe’s preferences towards
DCP as observed through their photophysical signaling responses.
In summary, 1 was shown to exhibit selective and sensitive
‘turn-on’ signaling in presence of DCP among various
organophosphates, through their signature spectral features
corresponding to DCP-induced spiro-ring opening. 2 also
exhibited similar DCP-induced photophysical signalling
There are no conflicts to declare.
Notes and references
‡ Crystallographic data: The CCDC no. for 1, 2 and 3 are
1963360, 1963358 and 1978815 respectively.
§ BPB wishes to thank to the Director, CSIR-IMMT Bhubaneswar
for requisite permissions and financial support through a CSIR
grant (CSIR-IMMT-MLP-040).
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responses whereas
3
did not show such spectral
enhancements with DCP. The study also revealed to formation
of diethyl phosphate derivatives of the probes (1 and 2)
through phosphorylation at carbonyl end on their spirolactam
4 | J. Name., 2012, 00, 1-3
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