Synthesis and Opto-electronic Properties of BODIPY o-OPhos Systems

Article abstract of DOI:10.1111/php.13306

Herein, we report the versatile synthetic strategy and opto-electronic properties for the phosphorylation of BODIPY derivatives 5aa-5ak by substituting with an electron-donating/withdrawing group at the ortho position. Nevertheless, this new methodology relatively promotes the tolerance of the aldehyde moiety and the high yield for the synthesis of BODIPY o-OPhos derivatives. The photophysical studies suggest improved optical properties due to the inductive effect of various electron-donating/withdrawing groups. The UV-visible and the emission data suggest that BODIPY o-OPhos derivatives emphasize the property of the excited states with an increase in fluorescence intensity and high quantum yields due to the presence of bulky phospsho-triester at the meso- position which hinders the free rotation around the C-Ar bond and facilitates the development of OLEDs and various organophosphorus warfare agents. Electrochemical studies reveal 5ak depicts the ease of redox activity amongst the 5aa-5ak derivatives. The density functional theory indicates the highest occupied molecular orbital on the BODIPY moiety whereas the lowest unoccupied molecular orbital delocalized on BODIPY and the phospho-triester moieties. Thus, the unique development of the novel BODIPY derivatives with improved optical and redox properties pave the way for fluorescent probes and bioimaging techniques.

Full text of DOI:10.1111/php.13306

PROF. GIRIBABU LINGAMALLU (Orcid ID : 0000-0001-5936-7729)
Article type : Research Article
Synthesis and Opto-electronic Properties of BODIPY o-OPhos Systems
Thipanni Anitha1,3, Madoori Mrinalini2,3, Damera Vani1,3, Seelam Prasanthkumar2,3, Kallu
Rajender Reddy*1,3, and Lingamallu Giribabu*2,3
1Catalysis & Fine Chemicals Division, CSIR-Indian Institute of Chemical Technology (IICT),
Tarnaka, Hyderabad-500007, Telangana, India
2 Polymer & Functional Materials Division, CSIR-Indian Institute of Chemical Technology (IICT),
Tarnaka, Hyderabad-500007, Telangana, India
3Academy of Scientific and Innovation Research (AcSIR), Ghaziabad, New Delhi 201002, India.
*Corresponding authors e-mail: rajender@iict.res.in, rajenderkallu@gmail.com, giribabu@iict.res.in
This article has been accepted for publication and undergone full peer review but has not been through
the copyediting, typesetting, pagination and proofreading process, which may lead to differences
between this version and the Version of Record. Please cite this article as doi: 10.1111/PHP.13306
This article is protected by copyright. All rights reserved

ABSTRACT
Herein, we report the versatile synthetic strategy and opto-electronic properties for the
phosphorylation of BODIPY derivatives 5aa-5ak by substituting with an electron
donating/withdrawing group at the ortho position. Nevertheless, this new methodology relatively
promotes the tolerance of the aldehyde moiety and the high yield for the synthesis of BODIPY o-
OPhos derivatives. The photophysical studies suggest improved optical properties due to the inductive
effect of various electron donating/withdrawing groups. The UV-visible and the emission data suggest
that BODIPY o-OPhos derivatives emphasize the property of the excited states with an increase in
fluorescence intensity and high quantum yields due to the presence of bulky phospsho-triester at the
meso- position which hinders the free rotation around the C-Ar bond and facilitates the development
of OLEDs and various organophosphorus warfare agents. Electrochemical studies reveal 5ak depicts
the ease of redox activity amongst the 5aa-5ak derivatives. The density functional theory indicates the
highest occupied molecular orbital on the BODIPY moiety whereas the lowest unoccupied molecular
orbital delocalized on BODIPY and the phospho-triester moieties. Thus, the unique development of
the novel BODIPY derivatives with improved optical and redox properties pave the way for
fluorescent probes and bioimaging techniques.
This article is protected by copyright. All rights reserved

INTRODUCTION
The BODIPY or boron-dipyrromethene dyes are distinguishable for their inimitable small Stokes shift,
high fluorescence quantum yields, habitually approaching 100% even in water, sharp absorption and
emission peaks to overall brightness, and highly soluble in a range of organic solvents (1). The
precision of modulating these opto-electronic properties of BODIPY act an important building block
of organic fluorophores exhibit distinctive properties such as extended absorption, enhanced
fluorescence emission, absolute quantum yields and better thermal/photostability. The characteristic
properties render BODIPY fluorophores proficient for many opto-electronic and biological
applications (2-9). Thereby utilized as emissive materials in OLEDs, sensitizers in dye-sensitized solar
cells, small molecule based donors in organic solar cells etc (10-13). Moreover, these fluorophores are
repeatedly used in biological applications for labeling nucleotides, amino acids and important tools in
imaging techniques (14-16). Furthermore, BODIPY fluorophores are recently applied in detecting
chemical warfare agents (CWAs) such as organophosphorus agents (OP) that include sarin, soman,
cyclosarin, and tabun are severely toxic chemicals aid to block the function of a key enzyme
acetylcholinesterase in neurotransmission that leads to paroxysm and eventually death by respiratory
paralysis (17-21). In this fluorescent probe for the detection of OP nerve agent the aromatic hydroxyl
group [2-(5,5-difluoro-5H-4λ4,5λ4-dipyrrolo[1,2,-c:2’1’-f][1,3,2]diazaborinin-10-yl)phenol], reacts
with the analyte yields a phosphate ester results in a fluorescent product (19). The non-fluorescent
nature of hydroxyl BODIPY is due to the free rotation around meso C-Ar bond and associated with
high nonradiative deactivation rates. The formation of bulky phosphate ester at ortho position of
phenyl ring of BODIPY sterically hinders the free rotation and restores the fluorescence with enriched
quantum yields. In this manuscript, we designed and synthesized a series of BODIPY fluorophores
with phosphate ester at ortho position of meso- phenyl and varying either electron releasing or
electron withdrawing groups. To get the phosphate ester of BODIPYs we performed the
phosphorylation of phenol derivatives by the reaction between salicylaldehyde and dialkyl phosphites
upon oxidation, however, the aldehyde moiety unaffected by phosphorylation bearing the phosphate
This article is protected by copyright. All rights reserved

ester (3aa to 3ao) further treated for the synthesis of BODIPY core (5aa to 5ak) as shown in Scheme
1 and 2, respectively (22). All the derivatives characterized by various spectroscopic techniques (1H
NMR, 13C NMR, 31P NMR, UV-Visible, fluorescence) and electrochemical methods.
MATERIALS AND METHODS
All chemicals and reagents were obtained commercially either from Sigma-Aldrich and Alfa Aesar used
without any further purification. Analytical reagent (AR) grade solvents used for the reactions while
laboratory reagent (LR) grade solvents utilized for further purifications and column chromatography (23).
All the reactions carried out under nitrogen or argon atmosphere using dry and degassed solvents.
1H Nuclear magnetic resonance (NMR) spectra of salicylaldehyde and BODIPY derivatives recorded
either on a 400 MHz and 500 MHz whereas 13C NMR and 31P NMR recorded on 100 MHz and 162 MHz
Avance spectrometer. The chemical shift values recorded in δ ppm with TMS using CDCl3 as internal
31
standard. The P NMR recorded using 85ꢀ% H3PO4 as external standard. The Electron spray ionization
high resolution mass spectrometer (ESI-HRMS) performed on The Waters 2996 Photodiode array
detector. The [M + H]+ fragments calculated and reported in m/z values. The UV-Vis absorption spectra
of BODIPY o-OPhos derivatives (5aa-5ak) were recorded in CH2Cl2 at a concentration of 1 × 10-5 M
using 1cm quartz cuvette on Shimadzu (Model UV-3600) spectrophotometer at room temperature. The
absorbance of the samples measured in region 250 – 800 nm. The steady-state fluorescence spectra of
solutions were recorded on Fluorolog-3 spectrofluorometer (Spex model, JobinYvon) at excitation
wavelength of 345 and 505 nm at room temperature. The emission maxima of the samples were measured
in wavelength range of 400-800 nm. The lifetime measurements performed on picoseconds time-
correlated single photon (TCSPC) setup of make model Fluoro Log3-Triple Illuminator, IBH Horiba
JobinYvon using a NanoLED of 484 nm (a picoseconds light emitting diode laser). The
photoluminescence decay profiles of the 5aa-5ak analysed as τ and apparent values calculated in ‘ns’.
Cyclic voltammetry experiments of BODIPY o-OPhos derivatives were performed on a PC-controlled CH
instruments model CHI 620C electrochemical analyzer in CH2Cl2 at scan rate of 100 mV/s using 0.1 M
tetrabutylammonium hexafluorophosphate (NBu4PF6)). The glassy carbon, standard calomel electrode
This article is protected by copyright. All rights reserved

(SCE) and platinum wire as the working reference and auxiliary electrode. The resultant I vs V plots
obtained for 5aa-5ak and the corresponding redox potentials calculated. Theoretical calculations of
BODIPY o-OPhos derivatives performed using density functional theory (DFT) calculations using the
Gaussian 09 package with a functional basis set of the B3LYP/6-31G (d, p) to determine the nature of
orbital energy levels and the electron donating/accepting ability of BODIPY derivatives in vacuum
confirmed the electron density distribution in BODIPY o-OPhos derivatives (5aa-5ak) (24-29).
Synthesis
General procedure for the phosphorylation of salicylaldehyde derivatives (3aa-3ao): A mixture of
salicylaldehyde (1.0 mmol), H-phosphonate (1.0 mmol) and LiI (1.0 mmol) were taken in 2 mL of MeCN
in a single–neck flask. To the above stirred solution 3.0 equiv. of 70% aq. TBHP added at room
temperature in an open-air atmosphere. The reaction mixture further stirred up to 15 min and progress of
reaction monitored by thin layer chromatography (TLC). The reaction mixture was diluted with ethyl
acetate and washed with sodium thiosulfate. The organic layer was separated and dried with anhydrous
Na2SO4. The excess solvent was removed under reduced pressure. The residue was purified by column
chromatography on silica gel (hexane/ethyl acetate) to afford the pure product. The product was
confirmed by 1H, 13C, 31P NMR, ESI-MS and HRMS analysis.
1
Diethyl (2-formylphenyl) phosphate (3aa): Light yellow oil; 194 mg, 75% yield); H NMR  (400
MHz, CDCl3): 10.40 (s, 1H), 7.90 (dt, J = 7.7, 1.4 Hz, 1H), 7.61 (td, J = 8.4, 1.8 Hz, 1H), 7.46 (td, J =
13
8.3, 0.9 Hz, 1H), 7.32 (dd, J = 7.7, 1.1 Hz, 1H), 4.19-4.32 (m, 4H), 1.36 (td, J = 7.5, 0.9 Hz, 6H); C
NMR  (100 MHz, CDCl3): 188.4, 152.8 (d, J = 6.5 Hz), 135.6, 128.7, 127.3 (d, J = 5.4 Hz), 125.3,
31
121.0, 65.1 (d, J = 5.4 Hz), 16.0 (d, J = 6.5 Hz); P NMR (162 MHz, CDCl3, ppm): δ -6.68; MS (ESI)
m/z = 259 (M+H)+; (ESI-HRMS) calculated for C11H16O5P (M+H)+: 259.07299, found: 259.07279.
1
4-Fluoro-2-formylphenyl diethyl phosphate (3ab): Light yellow oil; (210 mg, 76% yield); H NMR 
1
(400 MHz, CDCl3): H NMR  (400 MHz, CDCl3): 10.33 (s, 1H), 8.00 (dd, J = 2.5, 1.1 Hz, 1H), 7.69
(dd, J = 8.8, 2.5 Hz, 1H), 7.38 (dd, J = 8.8, 1.1 Hz, 1H), 4.19-4.32 (m, 4H), 1.36 (td, J = 7.5, 0.9 Hz, 6H);
13C NMR  (100 MHz, CDCl3): 187.3, 159.5 (d, J = 247.2 Hz), 148.7 (d, J = 6.6, Hz), 128.5(t, J = 5.8
Hz), 123.0 (d, J = 8.0 Hz), 122.4 (d, J = 24.2 Hz), 114.3 (d, J = 24.2 Hz), 65.2 (d, J = 5.8 Hz), 16.0 (d, J =
6.6 Hz); 31P NMR (162 MHz, CDCl3, ppm): δ -6.36; MS (ESI) m/z = 277 (M+H)+; (ESI-HRMS)
This article is protected by copyright. All rights reserved

calculated for C11H15O5FP (M+H)+: 277.06356, found: 277.06344.
1
4-Chloro-2-formylphenyl diethyl phosphate (3ac): Colour less oil; (219 mg, 75% yield); H NMR 
(400 MHz, CDCl3): 10.33 (s, 1H), 7.84 (dd, J = 2.6, 0.9 Hz, 1H), 7.54 (dd, J = 8.8, 2.6 Hz, 1H), 7.45 (dd,
13
J = 8.8, 1.1 Hz, 1H), 4.21-4.30 (m, 4H), 1.36 (td, J = 7.5, 1.1 Hz, 6H); C NMR  (100 MHz, CDCl3):
31
187.1, 151.1 (d, J = 6.6 Hz), 135.2, 131.2, 128.2, 122.7, 65.2 (d, J = 5.8 Hz), 16.0 (d, J = 6.6 Hz); P
NMR (162 MHz, CDCl3, ppm): δ -6.65; MS (ESI) m/z = 293 (M+H)+; (ESI-HRMS) calculated for
C11H15O5ClP (M+H)+: 293.03401, found: 293.03392.
4-Bromo-2-formylphenyl diethyl phosphate (3ad): Dark red oil; (201 mg, 60% yield); 1H NMR  (400
MHz, CDCl3): 10.32 (s, 1H), 8.00 (dd, J = 2.5, 1.1 Hz, 1H), 7.69 (dd, J = 8.8, 2.5 Hz, 1H), 7.38 (dd, J =
8.8, 1.1 Hz, 1H), 4.19-4.32 (m, 4H), 1.36 (td, J = 7.5, 0.9 Hz, 6H); 13C NMR  (100 MHz, CDCl3): 187.0,
151.6 (d, J = 6.6 Hz), 138.1, 131.3, 128.5 (d, J = 5.8 Hz), 123.0, 118.6, 65.2 (d, J = 5.8 Hz), 16.0 (d, J =
6.6 Hz); 31P NMR (162 MHz, CDCl3, ppm): δ -6.85; MS (ESI) m/z = 337 (M+H)+; (ESI-HRMS)
calculated for C11H15O5BrP (M+H)+: 336.98350, found: 336.98376.
Diethyl (2-formy-4-methylphenyl) phosphate (3ae): Light yellow oil; (223 mg, 82% yield); 1H NMR 
(500 MHz, CDCl3): 10.37 (s, 1H), 7.68 (s, 1H), 7.39 (dd, J = 8.5, 1.9 Hz, 1H), 7.34 (dd, J = 8.3, 0.7 Hz,
13
1H), 4.20-4.28 (m, 4H), 2.37 (s, 3H), 1.35 (td, J = 7.4, 1.0 Hz, 6H); C NMR  (100 MHz, CDCl3):
188.7, 150.7 (d, J = 7.3 Hz), 136.3, 135.2, 128.7, 126.9 (d, 5.8 Hz), 120.9, 65. 0 (d, J = 5.8 Hz), 20.5, 16.0
(d, J = 5.8 Hz); 31P NMR (162 MHz, CDCl3, ppm): δ -6.49; MS (ESI) m/z = 273 (M+H)+; (ESI-HRMS)
calculated for C12H18O5P (M+H)+: 273.08864, found: 273.08854.
1
Diethyl (2-formy-5-methylphenyl) phosphate (3af): Colour less oil; (212 mg, 77% yield); H NMR 
(400 MHz, CDCl3): 10.34 (s, 1H), 7.78 (d J = 7.9 Hz, 1H), 7.27 (s, 1H), 7.10 (d, J = 7.9 Hz, 1H), 4.21-
4.30 (m, 4H), 2.24 (s, 3H), 1.36 (t, J = 7.0, 6H); 13C NMR  (125 MHz, CDCl3): 188.2, 152.7 (d, J = 6.6
Hz), 147.4, 128.6, 126.3, 124.9 (d, J = 6.6 Hz), 121.3, 65.0 (d, J = 5.3 Hz), 21.9, 16.0 (d, J = 6.6 Hz); 31P
NMR (162 MHz, CDCl3, ppm): δ -6.55; MS (ESI) m/z = 273 (M+H)+; (ESI-HRMS) calculated for
C12H18O5P (M+H)+: 273.08864, found: 273.08855.
1
Diethyl (2-formy-5-methoxyphenyl) phosphate (3ag): Yellow oil; (199 mg, 69% yield); H NMR 
(400 MHz, CDCl3): 10.25 (s, 1H), 7.85 (dd, J = 8.8, 1.1 Hz, 1H), 6.98 (dd, J = 2.3, 1.1 Hz, 1H), 6.81 (dd,
13
J = 8.8, 2.4 Hz, 1H), 4.21-4.31 (m, 4H), 3.88 (s, 3H), 1.37 (td, J = 7.5, 0.9 Hz, 6H); C NMR  (100
This article is protected by copyright. All rights reserved

MHz, CDCl3): 187.1, 165.4, 154.4 (d, J = 6.6 Hz), 130.3, 120.8 (d, J = 5.8 Hz), 111.7, 105.9, 65. 1 (d, J
31
= 5.8 Hz), 55.8, 16.0 (d, J = 6.6 Hz); P NMR (162 MHz, CDCl3, ppm): δ -6.96; MS (ESI) m/z = 289
(M+H)+; (ESI-HRMS) calculated for C12H18O6P (M+H)+: 289.08355, found: 289.08350.
1
4-(Tert-butyl)-2-formylphenyl Diethyl phosphate (3ah): Light yellow oil; (220 mg, 70% yield); H
NMR  (400 MHz, CDCl3): 10.40 (s, 1H), 7.89 (dd, J = 2.5, 1.1 Hz, 1H), 7.62 (dd, J = 8.6, 2.6 Hz, 1H),
7.38 (dd, J = 8.6, 0.9 Hz, 1H), 4.20-4.30 (m, 4H), 1.30 (td, J = 7.4, 0.9 Hz, 6H), 1.32 (s, 9H); 13C NMR 
(100 MHz, CDCl3): 188.8, 150.6 (d, J = 6.6 Hz), 148.4, 132.9, 126.5 (d, J = 6.6 Hz), 125.2, 120.5, 65.0
31
(d, J = 5.8 Hz), 34.5, 31.1, 16.0 (d, J = 6.6 Hz); P NMR (162 MHz, CDCl3, ppm): δ -6.44; MS (ESI)
m/z = 315 (M+H)+; (ESI-HRMS) calculated for C15H24O5P (M+H)+: 315.13559, found: 315.13555.
1
5-(Diethylamino)-2-formylphenyl diethyl phosphate (3ai): Dark red oil; (221 mg, 67% yield); H
NMR  (500 MHz, CDCl3): 10.07 (s, 1H), 7.43 (dd, J = 2.2, 1.0 Hz, 1H), 6.62 (dd, J = 2.2, 1.0 Hz, 1H),
6.48 (dd, J = 9.0, 2.2 Hz, 1H), 4.20-4.28 (m, 4H), 3.42 (q, J = 10.0, 4H), 1.36 (td, J = 7.5, 1.0 Hz, 6H),
13
1.21 (t, J = 7.0, Hz, 6H); C NMR  (100 MHz, CDCl3): 186.1, 155.0 (d, J = 6.6 Hz), 153.2, 130.3,
115.4 (d, J = 5.8 Hz), 108.0, 101.5, 64.8 (d, J = 5.8 Hz), 44.8, 16.0 (d, J = 6.6 Hz), 12.3; 31P NMR (162
MHz, CDCl3, ppm): δ -6.80; MS (ESI) m/z = 330 (M+H)+; (ESI-HRMS) calculated for C15H25O5NP
(M+H)+: 330.14649, found: 330.14644.
1
4-Allyl-2-formyl-6-methoxyphenyl diethyl phosphate (3aj): Gray solid; (92 mg, 28% yield); H NMR
 (400 MHz, CDCl3): 10.37 (s, 1H), 7.28 (d, J = 2.0 Hz, 1H), 7.02 (d, J = 1.9 Hz, 1H), 5.87-5.97 (m, 1H),
5.12-5.14 (m, 1H), 5.08-5.11 (m, 1H), 4.22-4.31 (m, 4H), 3.91 (s, 3H), 3.40 (d, J = 6.7 Hz, 2H), 1.36 (td,
J = 7.5, 1.2 Hz, 6H); 13C NMR  (100 MHz, CDCl3): 189.1, 151.5 (d, J = 2.9 Hz), 140.9 (d, J = 8.0 Hz),
138.1, 136.1, 128.9 (d, J = 3.6 Hz), 119.0, 118.4, 116.8, 64.8 (d, J = 5.8 Hz), 56.3, 39.7, 16.0 (d, J = 6.6
Hz); 31P NMR (162 MHz, CDCl3, ppm): δ -6.06; MS (ESI) m/z = 329 (M+H)+; (ESI-HRMS) calculated
for C15H22O6P (M+H)+: 329.11485, found: 329.11489.
1
Diethyl (1-formylnaphthalen-2-yl) phosphate (3ak): Dark red oil; (154 mg, 50% yield); H NMR 
(400 MHz, CDCl3): 10.85 (s, 1H), 9.24 (d, J = 8.6 Hz, 1H), 8.09 (d, J = 9.0 Hz, 1H), 7.84 (d, J = 8.0 Hz,
13
1H), 7.61-7.69 (m, 2H), 7.53 (t, J = 7.2 Hz, 1H), 4.22-4.32 (m, 4H), 1.37 (td, J = 7.5, 0.8 Hz, 6H); C
NMR  (100 MHz, CDCl3): 190.9, 154.9 (d, J = 6.6 Hz), 136.9, 130.8 (d, J = 8.7 Hz), 129.8, 128.2,
126.3, 125.3, 120.3 (d, J = 6.6 Hz), 119.7, 65.2 (d, J = 5.8 Hz), 16.0 (d, J = 6.6 Hz); 31P NMR (162 MHz,
This article is protected by copyright. All rights reserved

CDCl3, ppm): δ -6.79; MS (ESI) m/z = 309 (M+H)+; (ESI-HRMS) calculated for C15H18O5P (M+H)+:
309.08864, found: 309.08853.
1
2-Formylphenyl dimethyl phosphate (3al): Light yellow oil; (120 mg, 52% yield); H NMR  (400
MHz, CDCl3): 10.40 (d, J = 0.7 Hz, 1H), 7.90 (dt, J = 9.1, 1.4 Hz, 1H), 7.61 (td, J = 8.7, 1.8 Hz, 1H),
7.45 (dt, J = 9.2, 0.9 Hz, 1H), 7.32 (t, J = 7.7 Hz, 1H), 3.92 (s, 3H), 3.90 (s, 3H); 13C NMR  (100 MHz,
CDCl3): 188.2, 152.3 (d, J = 6.6 Hz), 135.7, 129.0, 127.2 (d, J = 6.6 Hz), 125.5, 120.9, 55.2 (d, J = 5.8
Hz); 31P NMR (162 MHz, CDCl3, ppm): δ -4.45; MS (ESI) m/z = 231 (M+H)+; (ESI-HRMS) calculated
for C9H12O5P (M+H)+: 231.04169, found: 231.04168.
2-Formylphenyl diisopropyl phosphate (3am): Light yellow oil; (200 mg, 70% yield); 1H NMR  (400
MHz, CDCl3): 10.42 (s, 1H), 7.90 (dt, J = 9.2, 1.4 Hz, 1H), 7.59 (td, J = 9.0, 1.8 Hz, 1H), 7.49 (dt, J =
8.4, 1.1 Hz, 1H),7.28 (t, J = 7.8 Hz, 1H), 4.75-4.83 (m, 2H), 1.38 (d, J = 6.2 Hz, 6H), 1.31 (d, J = 6.2 Hz,
13
6H); C NMR  (100 MHz, CDCl3): 188.6, 153.0 (d, J = 7.3 Hz), 135.5, 128.4, 127.2 (d, J = 5.8 Hz),
125.1, 121.1, 74.1 (d, J = 5.8 Hz), 23.4 (d, J = 5.3 Hz); 31P NMR (162 MHz, CDCl3, ppm): δ -8.35; MS
(ESI) m/z = 287 (M+H)+; (ESI-HRMS) calculated for C13H20O5P (M+H)+: 287.10429, found:
287.10423.
1
Dibutyl (2-formylphenyl) phosphate (3an): Light yellow oil; (239 mg, 76% yield); H NMR  (400
MHz, CDCl3): 10.42 (d, J = 0.7 Hz, 1H), 7.90 (dt, J = 9.1, 1.4 Hz, 1H), 7.60 (td, J = 8.3, 1.8 Hz, 1H),
7.47 (dt, J = 8.3, 1.2 Hz, 1H), 7.30 (t, J = 7.8 Hz, 1H), 4.14-4.22 (m, 4H), 1.64-1.71 (m, 4H), 1.34-1.44
13
(m, 4H), 0.92 (t, J = 7.3 Hz, 6H); C NMR  (125 MHz, CDCl3): 188.4, 152.9 (d, J = 5.8 Hz), 135.6,
128.6, 127.2 (d, J = 5.8 Hz), 125.3, 121.0, 68.7 (d, J = 5.8 Hz), 32.1 (d, J = 5.8 Hz), 18.5, 13.4; 31P NMR
(162 MHz, CDCl3, ppm): δ -6.44; MS (ESI) m/z =315 (M+H)+; (ESI-HRMS) calculated for C15H24O5P
(M+H)+: 315.13559, found: 315.13551.
Ethyl (2-formylphenyl) phenylphosphonate (3ao): Color less oil; (148 mg, 51% yield); 1H NMR  (400
MHz, CDCl3): 10.34 (d, J = 0.7 Hz, 1H), 7.85-7.92 (m, 3H), 7.59-7.64 (m, 1H), 7.48-7.56 (m, 3H), 7.44
(d, J = 8.3 Hz, 1H), 7.26 (t, J = 7.6 Hz, 1H), 4.22-4.32 (m, 2H), 1.35 (t, J = 6.7 Hz, 3H); 13C NMR  (100
MHz, CDCl3): 188.5, 152.6 (d, J = 7.3 Hz), 135.5, 133.2, 131.7 (d, J = 10.2 Hz), 128.8, 128.6, (d, J = 5.1
Hz), 127.5 (d, J = 5.1 Hz), 125.1, 121.7, 63.5 (d, J = 5.8 Hz), 16.2 (d, J = 5.8 Hz); 31P NMR (162 MHz,
CDCl3, ppm): δ 16.07; MS (ESI) m/z = 291 (M+H)+; (ESI-HRMS) calculated for C15H26O4P (M+H)+:
This article is protected by copyright. All rights reserved

291.07807, found: 291.07796.
General procedure for synthesis BODIPY o-OPhos derivatives (5aa-5ak): The ortho-phosphate
coupled salicylaldehyde derivative 3a (2.05 mmol) and pyrrole 4a (3.43 g, 51 mmol) stirred at room
temperature under nitrogen atmosphere. Subsequently, two drops of trifluoroacetic acid were added and
reaction mixture stirred up to 10 min followed by quenching with 0.1 N NaOH and extracted with ethyl
acetate. The organic layer was separated and dried over anhydrous Na2SO4. The excess solvent removed
under reduced pressure and residue further purified by column chromatography on silica gel (hexane/ethyl
acetate) to afford the dipyrromethane intermediate as a white solid. DDQ (300 mg, 1.32 mmol) added to
the stirred solution of dipyrromethane dissolved in dry CH2Cl2 (50 mL) at room temperature under
nitrogen atmosphere. The stirring continued up to 6 h and Et3N (2 mL, 14.4 mmol) was added to the
solution, followed by the drop wise addition of BF3·OEt2 (3 mL, 24.3 mmol) and the solution was stirred
overnight. After the completion of reaction, the reaction mixture evaporated under reduced pressure. The
crude product was purified by column chromatography on silica gel using hexanes/ethyl acetate results
1
13
31
BODIPY o-OPhos derivatives. The product was confirmed by H, C, P NMR, ESI-MS and HRMS
analysis.
8-[2-Diethylphosphoryloxyphenyl]-4,4-difluoro-4-bora-3a,4a-diaza-s indacene (5aa): Red solid; (198
mg, 23% yield); 1H NMR  (400 MHz, CDCl3): 7.93 (s, 2H), 7.52-7.57 (m, 2H), 7.41 (d, J = 8.0 Hz, 1H),
7.29-7.35. (m, 1H), 6.86 (d, J = 4.1 Hz, 2H), 6.52 (d, J = 3.7 Hz, 2H), 3.81-3.94 (m, 4H), 1.13 (td, J = 7.0,
13
1.1 Hz, 6H); C NMR  (100 MHz, CDCl3): 148.2 (d, J = 6.6 Hz), 144.5, 142.2, 135.3, 131.6, 131.4,
125.1 (d, J = 7.3 Hz), 124.5, 120.5, 118.5, 64.7 (d, J = 6.6 Hz), 15.7 (d, J = 6.6 Hz); 31P NMR (162 MHz,
CDCl3, ppm): δ -7.40; MS (ESI) m/z = 421 (M+H)+; (ESI-HRMS) calculated for C19H21O4N2BF2P
(M+H)+: 421.12946, found: 421.14380.
8-[5-Fluoro,2-Diethylphosphoryloxyphenyl]-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene
(5ab):
Orange solid; (269 mg, 30% yield); 1H NMR  (500 MHz, CDCl3): 7.93 (s, 2H), 7.53 (dd, J = 9.1, 4.5 Hz,
1H), 7.22-7.26. (m, 1H), 7.16 (dd, J = 7.9, 3.2 Hz, 1H), 6.88 (d, J = 4.2 Hz, 2H), 6.54 (d, J = 4.1 Hz, 2H),
13
3.81-3.92 (m, 4H), 1.13 (td, J = 7.0, 1.0 Hz, 6H); C NMR  (125 MHz, CDCl3): 157.7-157.6 (d, J =
247.0 Hz), 145.0, 144.3 (d, J = 8.1 Hz), 140.4, 135.0, 131.3, 126.6 (t, J = 7.2 Hz), 122.1 (d, J = 7.2 Hz),
118.8, 118.3 (d, J = 6.3 Hz), 64.8 (d, J = 6.3 Hz), 15.7 (d, J = 6.3 Hz); 31P NMR (162 MHz, CDCl3, ppm):
This article is protected by copyright. All rights reserved

δ -7.12; MS (ESI) m/z = 439 (M+H)+; (ESI-HRMS) calculated for C19H20O4N2BF3P (M+H)+:
439.12004, found: 439.13338.
8-[5-Chloro,2-Diethylphosphoryloxyphenyl]-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene
(5ac):
Brown solid with green luster; (475 mg, 51% yield); 1H NMR  (400 MHz, CDCl3): 7.93 (s, 2H), 7.51 (d,
J = 1.4 Hz, 2H), 7.41 (s, 1H), 6.87 (d, J = 4.1 Hz, 2H), 6.54 (d, J = 4.0 Hz, 2H), 3.81-3.94 (m, 4H), 1.13
13
(td, J = 7.0, 1.1 Hz, 6H); C NMR  (125 MHz, CDCl3): 146.9 (d, J = 6.3 Hz), 145.1, 140.2, 135.1,
131.5, 131.3, 130.9, 130.2, 126.6 (d, J = 7.2 Hz), 121.8, 118.9, 64.9 (d, J = 7.2 Hz), 15.7 (d, J = 6.3 Hz);
31P NMR (162 MHz, CDCl3, ppm): δ -7.39; MS (ESI) m/z = 455 (M+H)+; (ESI-HRMS) calculated for
C19H20O4N2BClF2P (M+H)+: 455.09048, found: 455.09312.
8-[5-Bromo,2-Diethylphosphoryloxyphenyl]-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene
(5ad):
1
Brown solid with green luster; (408 mg, 40% yield); H NMR  (500 MHz, CDCl3): 7.93 (s, 2H), 7.65
(dd, J = 8.8, 2.4 Hz, 1H), 7.55 (dd, J = 2.4, 1.0 Hz, 1H), 7.45 (dd, J = 8.8, 1.0 Hz, 1H), 6.87 (d, J = 4.2
13
Hz, 2H), 6.54 (d, J = 4.1 Hz, 2H), 3.82-3.93 (m, 4H), 1.13 (td, J = 7.1, 1.0 Hz, 6H); C NMR  (100
MHz, CDCl3): 147.4 (d, J = 5.8 Hz), 145.1, 140.1, 135.0, 134.4, 133.7, 131.3, 127.0 (d, J = 7.3 Hz),
122.1, 118.9, 117.5, 64.9 (d, J = 6.6 Hz), 15.7 (d, J = 6.6 Hz); 31P NMR (162 MHz, CDCl3, ppm): δ -7.50;
MS (ESI) m/z = 499 (M+H)+; (ESI-HRMS) calculated for C19H20O4N2BBrF2P (M+H)+: 499.03997,
found: 499.04449.
8-[5-Methyl,2-Diethylphosphoryloxyphenyl]-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene
(5ae):
Brown solid with green luster; (170 mg, 19% yield); 1H NMR  (500 MHz, CDCl3): 7.91 (s, 2H), 7.42 (d,
J = 8.5 Hz, 1H), 7.33 (dd, J = 8.3, 2.3 Hz, 1H), 7.20 (s,1H), 6.88 (d, J = 4.1 Hz, 2H), 6.52 (d, J = 3.5 Hz,
13
2H), 3.80-3.91 (m, 4H), 2.39 (s, 3H), 1.12 (td, J = 7.0, 0.7 Hz, 6H); C NMR  (125 MHz, CDCl3):
146.0 (d, J = 6.3 Hz), 144.4, 142.5, 135.3, 134.4, 132.1, 131.7, 131.5, 124.9 (d, J = 7.2 Hz), 120.3, 118.5,
64.6 (d, J = 7.2 Hz), 20.6, 15.7 (d, J = 6.3 Hz); 31P NMR (162 MHz, CDCl3, ppm): δ -7.20; MS (ESI) m/z
= 435 (M+H)+; (ESI-HRMS) calculated for C20H23O4N2BF2P (M+H)+: 435.14511, found: 435.15714.
8-[4-Methyl, 2-Diethylphosphoryloxyphenyl]-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (5af):
Brown solid with green luster; (427 mg, 48% yield); 1H NMR  (400 MHz, CDCl3): 7.90 (s, 2H), 7.36 (s,
1H), 7.28 (d, J = 7.5, Hz, 1H), 7.12 (d, J = 7.8 Hz, 1H), 6.88 (d, J = 3.6 Hz, 2H), 6.51 (d, J = 4.0 Hz, 2H),
13
3.79-3.92 (m, 4H), 2.46 (s, 3H), 1.12 (t, J = 7.0 Hz, 6H); C NMR  (100 MHz, CDCl3): 148.0 (d, J =
This article is protected by copyright. All rights reserved

6.6 Hz), 144.2, 142.6, 135.4, 131.4, 131.2, 125.4, 124.2 (d, J = 6.6 Hz), 121.0, 118.4, 64.7 (d, J = 6.6
Hz), 21.4, 15.7 (d, J = 7.3 Hz); 31P NMR (162 MHz, CDCl3, ppm): δ -7.52; MS (ESI) m/z = 435 (M+H)+;
(ESI-HRMS) calculated for C20H23O4N2BF2P (M+H)+: 435.14511, found: 435.15689.
8-[4-Methoxy,2-Diethylphosphoryloxyphenyl]-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene
(5ag):
1
Brown solid with green luster; (305 mg, 33% yield); H NMR  (400 MHz, CDCl3): 7.89 (s, 2H), 7.33
(dd, J = 8.5, 1.1 Hz, 1H), 7.11 (dd, J = 2.3, 1.1 Hz, 1H), 6.90 (d, J = 4.1 Hz, 2H), 6.86 (dd, J = 8.5, 3.0
13
Hz, 1H), 6.51 (d, J = 4.1 Hz, 2H), 3.79-3.93 (m, 7H), 1.12 (td, J = 7.0, 0.9 Hz, 6H); C NMR  (100
MHz, CDCl3): 162.2, 149.2 (d, J = 6.6 Hz), 144.0, 142.6, 135.4, 132.3, 131.4, 118.3, 117.5 (d, J = 6.6
Hz), 110.7, 106.5, 64.7 (d, J = 6.6 Hz), 55.7, 15.7 (d, J = 6.6 Hz); 31P NMR (162 MHz, CDCl3, ppm): δ -
7.55; MS (ESI) m/z = 451 (M+H)+; (ESI-HRMS) calculated for C20H23O5N2BF2P (M+H)+: 451.14002,
found: 451.13531.
8-[5-Diethylamino,2-Diethylphosphoryloxyphenyl]-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene
(5ah): Purple solid; (352 mg, 35% yield); 1H NMR  (400 MHz, CDCl3): 7.84 (s, 2H), 7.26 (dd, J = 8.8,
1.1 Hz, 1H), 7.00 (d, J = 4.0 Hz, 2H), 6.79 (s, 1H), 6.54 (dd, J = 8.6, 1.9 Hz, 1H), 6.49 (dd, J = 4.0, 15
Hz, 2H), 3.76-3.90 (m, 4H), 3.43 (q, J = 7.0 Hz, 4H), 1.24 (t, J = 7.0 Hz, 6H), 1.09 (td, J = 6.9, 0.9 Hz,
13
6H); C NMR  (100 MHz, CDCl3): 150.6, 149.6 (d, J = 6.6 Hz), 144.1, 142.5, 135.4, 133.4, 131.2,
31
117.7, 112.0, 107.5, 103.5, 64.6 (d, J = 6.6 Hz), 44.7, 15.7 (d, J = 6.6 Hz), 12.4; P NMR (162 MHz,
CDCl3, ppm): δ -7.39; MS (ESI) m/z = 492 (M+H)+; (ESI-HRMS) calculated for C23H30O5N3BF2P
(M+H)+: 492.20296, found: 492.20325.
8-[2-Diethylphosphoryloxynapthyl]-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (5ai): Brown solid
with green luster; (280 mg, 29% yield); 1H NMR  (400 MHz, CDCl3): 8.40 (d, J = 9.0 Hz, 1H), 7.95 (s,
2H), 7.91 (d, J = 8.6 Hz, 1H), 7.73 (d, J = 9.0 Hz, 1H), 7.64 (d, J = 8.1 Hz, 1H), 7.43-7.51 m, 2H), 6.67
(d, J = 4.1Hz, 2H), 6.44 (d, J = 3.6 Hz, 2H), 3.85-3.94 (m, 4H), 1.16 (td, J = 7.0, 0.9 Hz, 6H); 13C NMR 
(100 MHz, CDCl3): 151.4 (d, J = 6.6 Hz), 146.3 (d, J = 6.6 Hz), 144.8, 141.3, 136.0, 133.3, 131.8, 131.3,
127.9, 127.8, 125.9, 125.5, 119.0, 118.7, 64.8 (d, J = 5.8 Hz), 15.8 (d, J = 6.6 Hz); 31P NMR (162 MHz,
CDCl3, ppm): δ -7.35; MS (ESI) m/z = 471 (M+H)+; (ESI-HRMS) calculated for C23H23O4N2BF2P
(M+H)+: 471.14511 found: 471.15865.
8-[2-Dimethylphosphoryloxyphenyl]-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (5aj): Black solid
This article is protected by copyright. All rights reserved

1
with green luster; (169 mg, 21% yield); H NMR  (400 MHz, CDCl3): 7.92 (s, 2H), 7.50-7.58 (m, 2H),
7.42 (d, J = 6.3 Hz, 1H), 7.33. (t, J = 7.5 Hz, 1H), 6.87 (d, J = 4.2 Hz, 2H), 6.53 (d, J = 4.0 Hz, 2H), 3.51
13
(d, J = 11.3 Hz, 6H); C NMR  (100 MHz, CDCl3): 148.0 (d, J = 6.6 Hz), 144.6, 142.0, 135.3, 131.7,
31
131.5 (d, J = 6.6 Hz), 125.2 (d, J = 6.6 Hz), 124.8, 120.6, 118.6, 54.8 (d, J = 6.6 Hz); P NMR (162
MHz, CDCl3, ppm): δ -5.18; MS (ESI) m/z = 393 (M+H)+; (ESI-HRMS) calculated for C17H17O4N2BF2P
(M+H)+: 393.09816, found: 393.11089.
8-[2-Isopropylphosphoryloxyphenyl]-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (5ak): Brown solid
with green luster; (212 mg, 23% yield); 1H NMR  (400 MHz, CDCl3): 7.91 (s, 2H), 7.61 (d, J = 8.3 Hz,
1H), 7.53 (td, J = 7.3,1.7 Hz, 1H), 7.40 (dt, J = 9.0,1.4 Hz, 1H), 7.30 (t, J = 7.4 Hz, 1H), 6.85 (d, J = 4.2
Hz, 2H), 6.51 (d, J = 3.5 Hz, 2H), 4.33-4.44 (m, 2H), 1.54 (d, J = 6.2 Hz, 6H), 1.09 (d, J = 6.1 Hz, 6H);
13C NMR  (100 MHz, CDCl3): 148.6 (d, J = 6.5 Hz), 144.5, 142.5, 135.4, 131.4 (t, J = 5.4 Hz), 125.0
31
(d, J = 7.6 Hz), 124.2, 120.1, 118.5, 74.0 (d, J = 7.6 Hz), 23.2 (dd, J = 14.1, 4.3 Hz); P NMR (162
MHz, CDCl3, ppm): δ -9.13; MS (ESI) m/z = 449 (M+H)+; (ESI-HRMS) calculated for C21H25O4N2BF2P
(M+H)+: 449.16076, found: 449.17662.
RESULTS AND DISCUSSION
Phosphorylation of the salicylaldehyde derivatives (3aa-3ao)
<Scheme 1>
In this report, we have focused on the phosphorylation of salicylaldehyde derivatives for the
preparation of 2-formyl aryl phosphate esters. Substrate scope of salicylaldehyde derivatives using
various dialkyl phosphites as shown in Scheme 1. We began our substrate scope using our previous
conditions, 1.0 mmol of salicylaldehyde 1a and 1.0 mmol of diethyl phosphite 2a in the presence of
1.0 equiv. of LiI and 3.0 equiv. of 70% aq TBHP at room temperature and provide the corresponding
O-P coupled product 3aa in 75% yield. (22) Halo substituted salicylaldehyde derivatives such as -F, -
Cl and -Br smoothly reacted with 2a, resulting in the desired coupling products in good yields with
good halo functional group tolerance (Scheme 1, 3ab-3ad). Salicylaldehyde bearing with electron
This article is protected by copyright. All rights reserved

donating substituent at different positions simply couple with 2a to afford respective phosphate esters
in good yields (Scheme 1, 3ae-3ag). In continuation, the reaction performed with bulky group
substituted 5-(tert-butyl) salicylaldehyde with 2a afforded the target product 3ah in 70% yield and this
result indicates that there is no steric effect on this transformation. Further, we examined the
reactivity of 4-(diethylamino)-2-hydroxybenzaldehyde and 5-allyl-2-hydroxy-3-methoxybenzaldehyde
with 2a, resulted 3ai and 3aj in 67% and 28% yields respectively. Similarly, 2-hydoxy-1-
naphthaldehyde could involve in this reaction with 2a and provided the corresponding coupling
product in 50% yield (Scheme 1, 3ak). In further extension of this protocol, the reaction examined
with different dialkyl phosphites with salicylaldehyde derivatives, furnished the respective products in
52-76% yields (Scheme 1, 3al-3an). Interestingly, ethyl phenylphosphinate reacted well with simple
salicylaldehyde and provided the 3ao in 51% yield (Scheme 1).
The synthesized phosphorylated salicylaldehyde substrates further treated as starting materials
for the synthesis of BODIPY o-OPhos derivatives (5aa-5ak). In 2016, Kim group prepared the
BODIPY o-OPhos for the detection of organophosphorus nerve agents (19). They initiated the
synthesis with salicylaldehyde and pyrrole to develop BODIPY o-OH, a fluorogenic probe. Later,
BODIPY o-OH probe upon phosphorylation using diethyl chlorophosphate and base resulted in the
formations of BODIPY o-OPhos. This compound ensured a great fluorescence “turn-on” response.
Taking a clue from this work as well as our previous work on phenol phosphate, however, we made
an attempt to synthesize the phosphate esters functionalized BODIPY derivatives at meso position.
<Scheme 2>
BODIPY o-OPhos derivatives were conveniently synthesized by simple condensation of
pyrrole (4a) with the corresponding dialkyl (2-formylaryl) phosphates, followed by oxidation and
treatment with BF3·OEt2. The crude product purified by column chromatography on silica gel using
hexane/ethyl acetate as the mobile phase to afford BODIPY o-OPhos derivatives 5aa-5ak in 19% -
51% yield. Moreover, the reaction performed between diethyl (2-formylphenyl) phosphate and pyrrole
under experimental conditions provides the corresponding BODIPY in 23% yield (Scheme 2 5aa). 5-
halo 2-formyl phenyl phosphate esters such as –F, -Cl and -Br well tolerated and afforded the
This article is protected by copyright. All rights reserved

respective BODIPY substrates in low to moderate yields (Scheme 2 5ab-5ad). Nevertheless, the 2-
formyl phenyl phosphate esters bearing electron donating substitutents reacted with pyrrole, furnished
the 5ae-5ah up to 48% yield. Gratifyingly, 2-formyl naphthyl phosphate esters provided the resultant
BODIPY o-OPhos with extended conjugation in 29% yield (Scheme 2 5ai). In addition, 2-formyl
phenyl dimethyl phosphate esters and diisopropyl phosphate esters could also react with 4a and
respective BODIPY o-OPhos substrates were obtained up to 23% yield (Scheme 2 5aj and 5ak). The
resulting products were isolated and characterized by various spectroscopic techniques (1H NMR, 13C
31
NMR, P NMR, HRMS analysis, absorption, emission that includes both steady-state emission and
singlet state lifetimes), theoretical methods and electrochemical methods. The structural integrity of
13
31
all BODIPY derivatives was confirmed by 1H NMR, C NMR, P NMR, and HRMS analysis (See
Supporting Information).
Theoretical Calculations
Theoretical calculations of 5aa-5ak were performed to evaluate the electron donating/ accepting
nature using density functional theory (DFT) calculations employing the Gaussian 09 package with a
functional basis set of the B3LYP/6-31G (d, p) to determine the orbital energy levels and electron
density distribution of BODIPY derivatives in vacuum (Table S1). Minimum energy conformation
suggests that highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbitals
(LUMO) lying on the BODIPY moiety due to discrepancy in electron density distribution amongst the
donor/acceptor units with LUMO energy levels extending towards the phosphate ester. The resulting
HOMO and LUMO values are in the range of -5.388 to -6.013 eV and -2.721 to -2.912 eV. The
calculated band gap values obtained were 2.667 – 3.103 eV attributed to N, N diethyl derivative depict
the lowest band gap of 2.667 eV due to strong +I effect designate the impact of electron releasing and
withdrawing ability on the band gap of BODIPY derivatives as shown in energy level diagram (Fig.
1). Thus, permit the modulating of opto-electronic properties for application in organic light emitting
diodes (Table S1) (30).
<Figure 1>
This article is protected by copyright. All rights reserved

Photophysical Studies
UV-visible optical absorption studies of BODIPY derivatives were performed in dichloromethane at a
concentration of 1 × 10-5 M. Absorption spectra of 5aa - 5ak showed the absorption maxima at 337
and 505 nm which were assigned to the localized aromatic π–π* transitions.(31-34) However, 5ai
possess aryl substituent depict red shift of high energy absorption band to 365 nm whereas 5ah
exhibits hypsochromic shift lower energy absorption band to 498 nm and the shoulder observed at 553
nm owing to the strong electron releasing ability of N, N diethyl moiety, increase the electron density
at the nitrogen atom, decrease the n–π* transition energy and thereby result the bathochromic shifts
towards the longer wavelength. Consequently, the presence of electron releasing or electron
withdrawing groups on meso- phenyl position of BODIPY showed less impact on absorption maxima
except in case of 5ah. Further the presence of various electron releasing groups of phosphate ester has
not much impact on ground state electronic properties (Fig. 2).
<Figure 2>
<Figure 3>
Later, emission studies of BODIPY derivatives were performed at excitation wavelength of 345 and
505 nm. 5aa - 5ak displayed the emission maxima at 519 nm, 521 nm and 526 nm. However, 5ag
showed the blue shift in emission maxima at 519 nm. The electron donating groups such as methyl on
ortho/para position in 5ae, 5af and n-methyl derivatives of phosphate ester depict the enhancement in
fluorescence intensity. In addition, 5ah displayed the quenching in the emission maxima whereas the
other BODIPY derivatives suggest negligible changes in the emission spectrum. Subsequently, the
fluorescence quantum yields of the BODIPY derivatives were calculated using BODIPY as reference
and the values are in range of 0.3–0.5 respectively (35,36). In contrast, the presence of –OH group at
its ortho position of meso- phenyl has promote free rotation around meso C-Ar bond of BODIPY and
become non-fluorescent (19). The singlet state energies (E0-0) of all BODIPY derivatives estimated
from excitation and emission spectra are presented in Table 1 and found in range of ~2.40 eV. Thus,
This article is protected by copyright. All rights reserved

these studies revealed that significant changes in excited state preoprty and high quantum yield
facilitates the remarkable candidates for OLEDs and biological applications (Fig. 3).
<Figure 4>
Eventually, the photoluminescence decay studied for the BODIPY derivatives using time
correlated single photon counting (TCSPC) experiments in CH2Cl2 performed using 484 nm LED
source and emission monitored at 521 nm exhibit monoexponential decay profiles and lifetime values
found typically in ns regime (37). The BODIPY derivatives 5aa, 5ac, 5ad displayed absolute lifetime
values between 4.66 and 5.22 ns, however, fluorine linked 5ab leads to decrease in lifetime values to
3.99 ns owing to strong –I effect. Furthermore, the increase in the electron density due to presence of
methyl group indicate minor increase in lifetime values from 4.90-5.22 ns for 5ae, 5af, 5ag, 5aj and
5ak. Nevertheless, 5ah suggest insignificant lifetime values whereas 5ai exhibits enhanced lifetime
values of 6.65 ns (Fig. 4). Thereby, the photophysical properties of the synthesized BODIPY
derivatives with altering inductive effect and extended π-conjugation point towards the importance of
variable electrophilicity on the BODIPY.
<Table 1>
Electrochemical Properties
The cyclic voltammetry studies carried out to understand the electrochemical behaviour of
BODIPY derivatives using glassy carbon, calomel electrode and platinum (Pt) wire as the respective
working, reference, auxiliary electrodes and supporting electrolyte (0.1 M NBu4PF6) in CH2Cl2 at a
scan rate of 100 mV/s. The electrochemical data were presented in Table 1. Each BODIPY o-OPhos
derivative undergoes one or two reversible reductions and quasi-reversible reductions under
experimental conditions. 5ab, 5ac, 5ad, 5ag, 5ai revealed that the oxidation potentials at 0.84 V and
1.29 V and reduction at -0.74 V, -0.82 and -1.09 V. 5ae and 5af suggest oxidation at 0.83-0.86 V and
reduction at -0.82 and 0.74 V respectively. Nonetheless, the methyl, ethyl, isopropyl linked phosphate-
BODIPY derivatives amongst them the methyl and isopropyl groups exhibit oxidation around 0.90 V
whereas the ethyl moiety at 0.71 V. On the other hand, 5ah reveal maximum redox potentials at 1.34
This article is protected by copyright. All rights reserved

V and -0.87 V. Thus, the redox potentials of BODIPY derivatives propose the better
oxidation/reduction tendency for 5ah due owing to electron withdrawing N, N diethyl linked BODIPY
sustain the modifications in photophysical and electrochemical properties (Fig. 5 and Table 1).
<Figure 5 >
Further we executed thermogravimetric analysis of these compounds to understand the thermal
stability, which are very essential for optoelectronic applications. For this reason, we have executed
thermal stability of BODIPY o-OPhos compounds by using thermogravimetric analyses. It was well
known in literature that BODIPY derivatives are thermally stable above 200oC.38 No mass loss is
almost observed for the samples below the 150oC temperature as shown in the Supporting
Information. The decomposition of samples starts at ~200oC and continues up to 250oC, weight loss in
this temperature range is ~30% that belongs to the loss of phosphate ester from BODIPY o-OPhos.
The second decomposition was also observed in between 250-300oC that corresponds to weight loss
hydroxyl group on meso- phenyl ring of BODIPY.
In summary, we highlighted the phosphorylation reaction to synthesize the BODIPY o-OPhos
derivatives linked electron donating and withdrawing substituents. The unambiguous approach
replaces the existing synthetic strategies to design various BODIPY derivatives. Additionally, the
photophysical and electrochemical studies exploited to understand the nature of
electrophilicity/nucleophilicity in BODIPY o-OPhos derivatives. Theoretical and photophysical
properties propose that 5aa-5ak linked electron donor/acceptor moieties such as methyl, ethyl,
isopropyl and halogens on BODIPY o-OPhos derivatives conspicuously affect the electron density
distribution, band gap and quantum yields as a consequence leads enhanced fluorescence and
photoluminiscence decay profiles. Cyclic voltammetric studies suggest readily oxidixable nature of
5ab, 5ac and 5ah derivatives initiate the changes in redox behaviour of BODIPY o-OPhos based -
conjugated system. Finally the thermal behavior suggests that BODIPY o-OPhos are stable >200oC.
Hence, the optical and electrochemical properties of BODIPY promote the development of OLEDs,
chemical warfare agents and biological applications.
This article is protected by copyright. All rights reserved

ACKNOWLEDGEMENTS:
T.A, D.V and M.M thank UGC, DST and CSIR for fellowships. S.P. gratefully acknowledges the
DST-Inspire Faculty fellowship program under the project code: (DST/INSPIRE/04/2015/001457).
L.G thanks to CSIR (MLP-0051 & MLP-0060) for financial support of this work. Authors thanks to
Dr. Pratyay Basak for helping TG/DTA data. K.R.R. thanks the Director, CSIR‐IICT, for financial
support. (Manuscript No. IICT/Pubs./2020/056)
SUPPORTING INFORMATION
Additional supporting information may be found online in the Supporting Information section at the
end of the article.
1. Characterization data of salicylaldehyde derivatives (3aa-3ao)
1
2. H, 13C, 31P NMR of salicyladehyde derivatives (3aa-3ao)
3. Characterization data of BODIPYo-OPhos derivatives (5aa-5ak)
1
4. H, 13C, 31P NMR of of BODIPYo-OPhos derivatives (5aa-5ak)
5. TGA/DTG spectra of investigated BODIPY o-Ophos with a heating rate 10oC min_1 under
nitrogen gas.
6. Theoretical calculations of BODIPYo-OPhos derivatives (5aa-5ak)
Table S1. The HOMO-LUMO energy level distribution in BODIPYo-OPhos derivatives
REFERENCES
1. Use the Liu, Z., Z. Jiang, M. Yan and X. Wang (2019) Recent Progress of BODIPY Dyes With
Aggregation-Induced Emission. Front. Chem. 7, 712.
2. Kaur, P., and S. Singh (2019) Recent Advances in the Application of BODIPY in Bioimaging
and Chemosensing. J. Mat. Chem. C, 7, 11361-11405.
This article is protected by copyright. All rights reserved

3. Kolemen, S. and E. U. Akkaya (2018) Reaction-based BODIPY Probes for Selective Bio-
Imaging. Coord. Chem. Rev., 354, 121-134.
4. Ho, D., R. Ozdemir, H. Kim, T. Earmme, H. Usta and Ch. Kim (2019) BODIPY-Based
Semiconducting Materials for Organic Bulk Heterojunction Photovoltaics and Thin-Film
Transistors. ChemPlusChem, 84, 18-37
5. Li, G., W.-W. Xiong, P. -Y. Gu, J. Cao, J. Zhu, R. Ganguly, Y. Li, A. C. Grimsdale and Q.
Zhang (2015) 1,5,9-Triaza-2,6,10-triphenylboracoronene: BN-Embedded Analogue of
Coronene, Org. Lett., 17, 560–563
6. Ni, Y. and J. Wu (2014) Far-red and Near Infrared BODIPY dyes: Synthesis and Applications
for Fluorescent pH Probes and Bio-Imaging. Org. Biomol. Chem., 12, 3774-3791.
7. Lu, H., J. Mack, Y. Yang and Z. Shen (2014) Structural Modification Strategies for the
Rational Design of Red/NIR Region BODIPYs. Chem. Soc. Rev. 43, 4778-4823.
8. Boens, N., V. Leen and W. Dehaen (2012) Fluorescent indicators based on BODIPY. Chem.
Soc. Rev., 41, 1130-1172.
9. Loudet, A. and K. Burgess (2007) BODIPY Dyes and Their Derivatives:ꢀ Syntheses and
Spectroscopic Properties. Chem. Rev., 107, 4891-4932.
10. Shah, Md. F., A. Mirloup, T. H. Chowdhury, S. Alexandra, A. S. Hanbazazah, A. Ahmed, J. –
J. Lee, N. Leclerc, M. A. Shakour and A. Islam (2019) A Near-Infrared Thienyl-BODIPY Co-
Sensitizer for High-Efficiency Dye-Sensitized Solar Cells. Sustain. Energy Fuels, 3, 2983-
2989.
11. Chapran, M., E. Angioni, N. J. Findlay, B. Breig, V. Cherpak, P. Stakhira, T. Tuttle, D.
Volyniuk, J. V. Graulevicius, Y. A. Nastishin, O. D. Lavrentovich and P. J. Skabara (2017) An
This article is protected by copyright. All rights reserved

Ambipolar BODIPY Derivative for a White Exciplex OLED and Cholesteric Liquid Crystal
Laser toward Multifunctional Devices. ACS Appl. Mater. Interfaces, 9, 4750-4757.
12. Rao, R. S., A. Bagui, G. H. Rao, V. Gupta and S. P. Singh (2017) Achieving the Highest
Efficiency Using a BODIPY Core Decorated With Dithiafulvalene Wings for Small Molecule
Based Solution-Processed Organic Solar Cells. Chem. Commun., 53, 6953-6956.
13. Yang, B., J. Xiao, J. I. Wong, J. Guo, Y. Wu, L. Ong, L. L. Lao, F. Boey, H. Zhang, H. Y.
Yang and Q. Zhang (2011) Shape-Controlled Micro/Nanostructures of 9,10-
Diphenylanthracene (DPA) and Their Application in Light-Emitting Devices. J. Phys. Chem.
C., 115, 7924–7927.
14. Bui, H. T., D. K. Mai, B. Kim, K. –H. Choi, B. J. Park, H. –J. Kim and S. Cho (2019) Effect
of Substituents on the Photophysical Properties and Bioimaging Application of BODIPY
Derivatives with Triphenylamine Substituents. J. Phys. Chem. B, 123, 5601-5607.
15. Sun, J., H. Yang, O. Simalou, K. Lv, L. Zhai, J. Zhao and R. Lu (2019)
Mechanofluorochromic Behaviors of Triphenylamine Functionalized Salicylaldimine
Difluoroboron Complexes. New J. Chem., 43, 10134-1014.
16. Li, Y., N. Song, L. Chen, S. Liu and Z. Xie (2017) Synthesis of a Near‐Infrared BODIPY Dye
for Bioimaging and Photothermal Therapy. Chem. Asian J., 13, 989-995.
17. Jang, Y., T. –I. Kim, H. Kim, Y. Choi and Y. Kim (2019) Synthesis of a Near‐Infrared
BODIPY Dye for Bioimaging and Photothermal Therapy. ACS Appl. Bio Mater., 2,
2567−2572.
18. Lu, Z., W. Fan, X. Shi, C. A. Black, C. Fan and F. Wang (2018) A Highly Specific BODIPY-
Based Fluorescent Probe for the Detection of Nerve-Agent Simulants. Sens. Actuator B:
Chem., 255, 176-182.
This article is protected by copyright. All rights reserved

19. Kim, T. –I., S. B. Maity, J. Bouffard and Y. Kim (2016) Molecular Rotors for the Detection of
Chemical Warfare Agent Simulants. Anal. Chem., 88, 9259-9263.
20. Roacho, R. I., A. J. Metta-Magaña, E. Peña-Cabrera and K. H. Pannell (2013) Synthesis,
structural characterization, and spectroscopic properties of the ortho, meta, and para isomers
of 8‐(HOCH2‐C6H4)‐BODIPY and 8‐(MeOC6H4)‐BODIPY, J. Phys. Org. Chem., 26,
345−351.
21. Hu, R., E. Lager, A. Aguilar-Aguilar, J. Liu, J. W. Y. Lam, H. H. Y. Sung, I. D. Williams, Y.
Zhong, K. S. Wong, E. Peña-Cabrera and B. Z. Tang (2009) Twisted Intramolecular Charge
Transfer and Aggregation-Induced Emission of BODIPY Derivatives. J. Phys. Chem. C, 113,
15845−15853.
22. Anitha, T., K. C. Ashalu, M. Sandeep, A. Mohd, J. Wencel-Delord, F. Colobert and K. R.
Reddy (2019) LiI/TBHP Mediated Oxidative Cross‐Coupling of P (O)–H Compounds with
Phenols and Various Nucleophiles: Direct Access to the Synthesis of Organophosphates. Eur.
J. Org. Chem., 2019, 7463-7474.
23. Perrin, D. D., W. L. F. Armarego and D. R. Perrin (1980) Purification ofLaboratory
Chemicals, Oxford, UK.
24. Frisch, M. J., G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. Robb, A. J. R. Cheeseman, V.
G. Zakrzewski, J. A. Montgomery, R. E. Stratmann, J. C. Burant, S. Dapprich, J. M. Millam,
A. D. Daniels, K. N. Kudin, M. C. Strain, O. Farkas, et al., (2009) Gaussian 09, Gaussian,
Inc., Pittsburgh PA,
25. Dennington, R., T. Keith and J. Millam (2009) GaussView, version 5, Semichem Inc.,
Shawnee Mission KS.
26. O’Boyle, N. M., A. L. Tenderholt and K. M. Langner (2008) cclib: A Library for Package-
Independent Computational Chemistry Algorithms. J. Comput. Chem., 29, 839–845.
This article is protected by copyright. All rights reserved

27. Cossi, M., V. Barone, R. Cammi and J. Tomasi (1996) Ab Initio Study of Solvated
Molecules: A New Implementation of the Polarizable Continuum Model. Chem. Phys. Lett.,
255, 327–335.
28. Becke, D., (1993) Density‐Functional Thermochemistry. III. The Role of Exact Exchange. J.
Chem. Phys., 98, 5648–5652.
29. Peterson, G. A., and M. A. Al-Laham (1991) A Complete Basis Set Model Chemistry. II.
Open‐Shell Systems and The Total Energies of the First‐Row Atoms. J. Chem. Phys., 94,
6081–6090.
30. Sunahara, H., Y. Urano, H. Kojima and T. Nagano (2007) Design and Synthesis of a Library
of BODIPY-Based Environmental Polarity Sensors Utilizing Photoinduced Electron-Transfer-
Controlled Fluorescence ON/OFF Switching. J. Am. Chem. Soc., 129, 5597-5604.
31. Li, J., C. Yang, X. Peng, Y. Chen, Q. Qi, X. Luo, W.-Y. Lai and W. Huang (2018) Stimuli-
Responsive Solid-State Emission from o-Carborane–Tetraphenylethene Dyads induced by
Twisted Intramolecular Charge Transfer in the Crystalline State. J. Mater. Chem. C., 6, 19-28.
32. Li, J., X. Peng, C. Huang, Q. Qi, W.-Y. Lai and W. Huang (2018) Control of Circularly
Polarized Luminescence from a Boron Ketoiminate-based π-Conjugated Polymer via
Conformational Locks. Polym. Chem., 9, 5278–5285.
33. Wan, Y., J. Li, X. Peng, C. Huang, Q. Qi, W.-Y. Lai and W. Huang (2017) Intramolecular
Charge Transfer induced Emission from Triphenylamine-o-Carborane Dyads. RSC Adv., 7,
35543–35548.
34. Duvva, N., K. Sudhakar, D. Badgujar, R. Chitta and L. Giribabu (2015) Spacer Controlled
Photo-Induced Intramolecular Electron Transfer in a Series of Phenothiazine-Boron
Dipyrromethene Donor–Acceptor Dyads. J. Photochem. Photobiol. A: Chem., 312, 8-19.
This article is protected by copyright. All rights reserved

35. Giribabu, L., K. Jain, K. Sudhakar, N. Duvva and R. Chitta (2016) Light Induced
Intramolecular Electron and Energy Transfer Events in Rigidly Linked Borondipyrromethene:
Corrole Dyad. J. Lumin., 177, 209−218.
36. Aijun, C., X. Peng, J. Fan, X. Chen, Y. Wu and B. Guo (2007) Synthesis, Spectral Properties
and Photostability of Novel Boron–Dipyrromethene Dyes. J. Photochem. Photobiol. A: Chem.,
186, 85–92.
37. Soni, D., N. Duvva, D. Badgujar, T. K. Roy, S. Nimesh, G. Arya, L. Giribabu and R. Chitta
(2018) Hypochlorite-Mediated Modulation of Photoinduced Electron Transfer in a
Phenothiazine-Boron Dipyrromethene Electron Donor-Acceptor Dyad: A Highly Water
Soluble "Turn-On" Fluorescent Probe for Hypochlorite, Chem. Asian J., 13, 1594-1608.
38. Bumagina, N. A., A. Kriskaya, E. V. Anita, M. B. Berezin and A. I. V’yugin (2018) Effect of
Aklyl, Aryl, and meso-Aza Substitution on the Thermal Stability of BODIPY. Rus. J. Inorg.
Chem. 63, 1326-1332.
FIGURE CAPTIONS
Scheme 1. Phosphorylation of salicylaldehyde derivatives under oxidative conditions.
Scheme 2. Substrate scope of BODIPY o-OPhos derivatives.
Figure 1. HOMO-LUMO energy levels of BODIPY o-Ophos derivatives.
This article is protected by copyright. All rights reserved

Figure 2. UV-vis optical absorption spectra of BODIPY o-OPhos derivatives 5aa-5ak in
CH2Cl2 at a concentration of 1×10-4 M.
Figure 3. Emission studies of BODIPY o-OPhos derivatives 5aa-5ak in CH2Cl2 at excitation
wavelengths of a) 345 and b) 505 nm.
Figure 4. Photoluminescence decay profiles of BODIPY o-OPhos derivatives 5aa-5ak in CH2Cl2 at
an excitation wavelength of 484 nm LED source at 25 °C.
Figure 5. Cyclic Voltammetry of BODIPY o-OPhos derivatives 5aa-5ak in CH2Cl2 in 0.1 M
NBu4PF6 at a scan rate of 100 mV/s.
This article is protected by copyright. All rights reserved

Table 1. Photophysical, electrochemical, band gap and quantum yield calculations of
BODIPY o-OPhos derivatives
a
b
d
c
(ns)
BODIPY
o-Ophos
derivative
λ abs
λ ems
E0-0
Oxidation
potential
(V)e
Reduction HOMO LUMO
potential
(V)f
Band Gap Quantum
(nm) (nm)
(eV)
(eV)g
(eV)h
(eV)i
yield
(Φ)j
2.421
2.409
2.409
2.409
2.421
2.416
2.421
-
5aa
5ab
5ac
5ad
5ae
5af
505
505
505
505
505
505
505
520
525
525
525
520
522
520
-
5.22
3.96
4.66
4.51
5.03
4.90
4.41
-
0.71
0.87
-0.87
-0.74, -1.09
-0.82
-5.877
-5.959
-6.013
-5.986
-5.877
-5.877
-5.987
-5.388
-2.776
-2.857
-2.911
-2.884
-2.775
-2.775
-2.884
-2.721
3.101
3.102
3.102
3.102
3.102
3.102
3.103
2.667
0.50
0.32
0.48
0.36
0.48
0.49
0.50
0
0.84
0.87
-0.74, -1.09
-0.74
0.86
0.83
-0.82
5ag
5ah
0.89, 1.29
1, 1.34
-0.82
498,
553
-0.87
2.415
5ai
5aj
5ak
505
505
505
522
522
522
6.65
4.25
5.51
0.51, 0.82
0.90
-0.80
-0.34, -0.79
-0.83
-5.823
-5.877
-5.986
-2.721
-2.775
-2.884
3.102
3.112
3.102
0.51
0.50
0.49
2.416
2.416
0.87
aUV-Visible absorption maxima values recorded in CH2Cl2.
bEmission maxima values obtained in CH2Cl2 at 25°C.
cLifetime values studied in CH2Cl2 at 25°C using 484 nm LED source.
d Singlet state energies as estimated by the intersection between the absorption and the emission spectra (int: E0-0 –1240/int).
e, f The oxidation and reduction potentials from cyclic voltammograms of BODIPY o-OPhos derivatives performed at a scan rate
of 200 mV s−1 in CH2Cl2 using 0.1 M tetrabutylammonium hexafluorophosphate (TBAPF6).
g,h HOMO and LUMO energy level calculations using the Gaussian 09 package with a functional basis set of the B3LYP/6-31G
(d, p).
iBand gap values calculated from the optimized dye structures using EHOMO-ELUMO
.
jFluorescence quantum yield calculations by integrating the fluorescence bands using BODIPY as a reference.
This article is protected by copyright. All rights reserved

php_13306_f1.jpg
This article is protected by copyright. All rights reserved

php_13306_f2.jpg
This article is protected by copyright. All rights reserved

php_13306_f3.jpg
This article is protected by copyright. All rights reserved

php_13306_f4.jpg
This article is protected by copyright. All rights reserved

php_13306_f5.jpg
This article is protected by copyright. All rights reserved