Theoretical interpretation of electronic absorption and emission transitions in 9-acridinones

Article abstract of DOI:10.1016/S1386-1425(02)00195-6

Stationary absorption, fluorescence excitation and fluorescence spectra for 9(10H)-acridinone, 9(10-methyl)-acridinone, 2-methyl-9(10-methyl)-acridinone, 2-nitro-9(10-methyl)-acridinone, 9(10-ethyl)-acridinone and 9(10-phenyl)-acridinone dissolved in 1,4-dioxane, methyl alcohol or acetonitrile, as well as the available spectral characteristics reported by others were compared with those predicted theoretically at the semi-empirical PM3/CI (including the solvent effect within the COSMO model) or PM3/S levels of theory, in order to interpret spectral features of the compounds, i.e. the energies and probabilities of S₀ → S_n, S₀ → T₁, T₁ → T₂, S₁ → S₀, T₁ → S₀ and S₁ → T₁ transitions. Calculations at the PM3 and PM3/CI levels of theory enabled the structural changes accompanying S₀ → S₁, S₁ → T₁ and T₁ → S₀ transitions to be investigated; they yielded, moreover, basic physicochemical characteristics of the molecules in the ground and excited electronic states. Theoretically predicted dipole moments and charge distributions in the S₀, S₁ and T₁ states provided further insight into the nature of electronic transitions in 9-acridinones. The predicted characteristics correlate quite well with the available experimental ones, thus providing confirmation of the utility of theory in predicting the features of electronically excited molecules and interpreting the electronic transitions occurring in them.

Full text of DOI:10.1016/S1386-1425(02)00195-6

Spectrochimica Acta Part A 59 (2003) 543ꢁ558
/
www.elsevier.com/locate/saa
Theoretical interpretation of electronic absorption and
emission transitions in 9-acridinones
a
a
b
a,
A. Bou z˙ yk , L. J o´ z´ wiak , A.Yu. Kolendo , J. Bla z˙ ejowski ꢀ
a
Department of Chemistry, University of Gda n´ sk, Sobieskiego 18, 80-952 Gda n´ sk, Poland
b
Department of Chemistry, Kyiv Taras Shevchenko National University, 01033 Kiev, Volodymyrska 64, Ukraine
Received 4 January 2002; received in revised form 10 May 2002; accepted 13 May 2002
Abstract
Stationary absorption, fluorescence excitation and fluorescence spectra for 9(10H)-acridinone, 9(10-methyl)-
acridinone, 2-methyl-9(10-methyl)-acridinone, 2-nitro-9(10-methyl)-acridinone, 9(10-ethyl)-acridinone and 9(10-phen-
yl)-acridinone dissolved in 1,4-dioxane, methyl alcohol or acetonitrile, as well as the available spectral characteristics
reported by others were compared with those predicted theoretically at the semi-empirical PM3/CI (including the
solvent effect within the COSMO model) or PM3/S levels of theory, in order to interpret spectral features of the
compounds, i.e. the energies and probabilities of S 0
/
S , S 0
/
T , T 0
/
T , S 0
/
S , T 0
/
S and S 0
/
T transitions.
1
0
n
0
1
1
2
1
0
1
0
1
Calculations at the PM3 and PM3/CI levels of theory enabled the structural changes accompanying S
0
0
/
S
1
, S
and T transitions to be investigated; they yielded, moreover, basic physicochemical characteristics of the
1
0/T
1
1
0/S
0
molecules in the ground and excited electronic states. Theoretically predicted dipole moments and charge distributions
in the S , S and T states provided further insight into the nature of electronic transitions in 9-acridinones. The
0
1
1
predicted characteristics correlate quite well with the available experimental ones, thus providing confirmation of the
utility of theory in predicting the features of electronically excited molecules and interpreting the electronic transitions
occurring in them.
#
2002 Elsevier Science B.V. All rights reserved.
Keywords: 9-acridinones; Electronic absorption and emission spectra (transitions); Theory; Interpretation; Features of excited states
1
. Introduction
-Acridinones are heterocyclic compounds con-
these molecules the ability to interact specifically
with other molecules from their immediate sur-
roundings [1,2]. These compounds are therefore
convenient models for investigating the features of
entities that are at once aromatic amines and
ketones. Of particular interest is the ability of 9-
9
taining secondary or tertiary amino and keto
fragments within the ring system that confer on
acridinones to absorb UVꢁVIS radiation and emit
it efficiently in the short-wavelength visible region.
The absorption of gaseous 9(10H)-acridinone and
/
ꢀ
8-3410357
Corresponding author. Tel.: ꢂ
/
48-58-3450331; fax: ꢂ
/
48-
5
E-mail
address:
bla@chemik.chem.univ.gda.pl
(J.
9(10-methyl)-acridinone [3], the absorption of
Bla z˙ ejowski).
1386-1425/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 1 3 8 6 - 1 4 2 5 ( 0 2 ) 0 0 1 9 5 - 6

544
A. Bou z˙ yk et al. / Spectrochimica Acta Part A 59 (2003) 543ꢁ558
/
these compounds and their derivatives dissolved or
dispersed in media of different polarities, and their
ability to undergo specific interactions have been
fluorescence quantum yield is close to unity in
protic media, above 10% in specifically interacting
polar media, and of the order of a few percent in
neutral solvents such as aliphatic or aromatic
hydrocarbons [20,22,28,29,32]. In relation to this,
fluorescence lifetimes are of the order of nano or
several nanoseconds, while phosphorescence life-
times are measured in seconds [20,22,28,29,32]. It
is ought to be mentioned additionally that not only
thoroughly investigated [4ꢁ
gations have been focused on the photolumines-
cence [10,11,13,15,18ꢁ34] or chemiluminescence
15,35ꢁ40] of electronically excited 9-acridinones
/
17]. Numerous investi-
/
[
/
formed, in the latter case, during highly exother-
mic reactions of 9-substituted acridines with oxi-
dants. The position of the fluorescence bands
depends on the properties of the medium
T 0
/T absorption [17,21,22,26,30,41,42], but also
2
1
the absorption [1,12,15,18,19,34] and emission
[7,15,18,19,23,34] of anionic [1,7,15] and cationic
[12,15,18,19,23,34] forms of 9-acridinones have
[10,11,20,24], the temperature [22,24,25], and the
concentration of the emitting entities [25]. The
Fig. 1. The compounds investigated: 1*
-nitro-9(10-methyl)-acridinone; 5*9(10-ethyl)-acridinone; and 6*
indicated.
/
9(10H)-acridinone; 2*
/
9(10-methyl)-acridinone; 3*
/
2-methyl-9(10-methyl)-acridinone; 4*
/
2
/
/9(10-phenyl)-acridinone. The numbering of the atoms is

A. Bou z˙ yk et al. / Spectrochimica Acta Part A 59 (2003) 543ꢁ
/558
545
spectroscopy of 9-acridinones is quite well under-
stood. This is indeed true with regard to our
empirical knowledge of this subject. Theory, on
the other hand, has been applied only sporadically.
Thus, Sakhno et al. employed CNDO/S and
INDO/S methods to predict the wavenumbers of
electronic transitions in 9(10H)-acridinone [27],
while Ishijima et al. calculated the energies of
electronic transitions and oscillator strengths in
this compound using PPP and CNDO/S methods
with a view to interpret its MCD spectra [43]. SCF
MO LCAO calculations with the solvent simulated
by an external uniform electric field were also
carried out by Korotkova et al. [33] and Sakhno et
al. [44] in attempts to account for differences in the
fluorescence spectra of 9(10H)-acridinone in polar
and non-polar solvents. Attention in the present
publication is focused on the use of theory to
predict the structure and properties of six 9-
acridinones in excited S and T states in relation
1
1
to those in the ground (S ) state and to interpret
0
the features of S 0
/
S , S 0
/
T , T 0
/
T , S 0
/
S ,
0
0
n
0
1
1
2
1
T 0
/S
and S 0
/
T1 transitions. We have also
1
0
1
recorded absorption, fluorescence excitation and
fluorescence spectra of these compounds, which
provided us with the opportunity to compare our
own and other available experimental information
with that arising out of theoretical predictions.
2. Materials and methods
2.1. Chemicals
9
(10H)-acridinone (99%) (1) was purchased
from SigmaꢁAldrich. 9(10-Methyl)-acridinone (2)
was synthesized by the reaction of acridine with
dimethyl sulphate [45]. 2-Methyl-9(10H)-
/
acridinone was prepared following the method
proposed by Drozdov [46]. Accordingly, 2-bromo-
benzoic acid was initially heated with p-toluidine
in the presence of potassium carbonate. The
product obtained was subsequently subjected to
.
. .. . .
Fig. 2. Absorption (*
fluorescence (----) spectra of 1 in 1,4-dioxane (a), CH
and CH
/
), fluorescence excitation (
) and
OH (b)
3
3
CN (c), together with theoretically predicted excitation
(
j, ', ) and emission (I, ^, ) transitions (values for the
cyclization in the presence of POCl to yield 2-
3
gaseous phase are represented by ' and ^ in (b)). PM3/S,
lower values; PM3/CI, higher values.
methyl-9-acridinone. The final product, 2-methyl-
9(10-methyl)-acridinone (3), was prepared by the
reaction of 2-methyl-9-acridinone with dimethyl
been investigated in the past. The above brief
review leaves the impression that the electron
sulphate [47]. Nitration of 2 (at 100 8C) yielded a

546
A. Bou z˙ yk et al. / Spectrochimica Acta Part A 59 (2003) 543ꢁ558
/
hot acetic acid [48]. 9(10-Ethyl)-acridinone (5) was
obtained in the reaction of 1 with iodoethane [49].
The first step in the synthesis of 9(10-phenyl)-
acridinone (6) was the condensation of phenyla-
mine with 2-bromobenzoic acid in the presence of
powdered Cu as catalyst and potassium carbonate
[
46]. The 2-(N-phenylamino)benzoic acid product
was then condensed with iodobenzene to yield 2-
N,N-diphenylamino)benzoic acid [49], the iden-
(
tity of which was confirmed by X-ray analysis [50].
The final product (6) was obtained by cyclizing the
latter compound in the presence of sulphuric acid
[
51]. All substances were repeatedly recrystallized
from ethanol before use. The purity of the
compounds was verified by TLC and their chemi-
cal composition ascertained by elemental analysis
and NMR spectroscopy [52].
2.2. Measurements
The absorption and steady-state fluorescence
spectra were recorded on a Perkinꢁ/Elmer Lambda
18 spectrophotometer and LS-50 spectrofluorom-
eter, respectively. The emission spectra were mea-
sured by adjusting the excitation wavelengths to
the short-wavelength maxima in the absorption
spectra, while fluorescence excitation spectra were
recorded at wavelengths corresponding to the
maxima in the emission spectra. Band intensity
3
in the absorption spectra is given by o (in dm
ꢃ1
ꢃ1
mol cm ), while the intensities of fluorescence
excitation and fluorescence spectra are in arbitrary
units.
Spectral grade 1,4-dioxane, methyl alcohol and
acetonitrile, all from Fluka, were used as solvents
in all the spectroscopic measurements.
2.3. Quantum mechanical calculations
.
. .. . .
Fig. 3. Absorption (*
fluorescence (----) spectra of 2 in 1,4-dioxane (a), CH
and CH
/
), fluorescence excitation (
) and
OH (b)
Unconstrained geometry optimizations of mo-
lecules (Fig. 1) in the ground (S ) and excited
3
0
3
CN (c), together with theoretically predicted excitation
singlet (S ) or triplet (T ) electronic states were
1
1
(
j, ', ) and emission (I, ^, ) transitions in the gaseous
carried out at the semi-empirical PM3 (S state)
0
3
phase (b) and CH CN (c). PM3/S, lower values; PM3/CI,
and PM3/CI (S or T states) levels of theory [53],
1
higher values.
1
with standard procedures being employed together
with the EF method [54,55] implemented in
MOPAC 93 program package [56]. On completion
of each optimization, the Hessian matrix was
mixture of the 2-nitro (85%) (4) and 4-nitro (15%)
isomers, which were separated on the basis of
solubility differences between the compounds in

A. Bou z˙ yk et al. / Spectrochimica Acta Part A 59 (2003) 543ꢁ
/558
547
true minima [57]. The MOPAC 93 routines were
then used to predict the thermochemical and
physicochemical quantities for the compounds
under investigation [56,57]. Solvent (1,4-dioxane,
CH OH, CH CN) effects were included in the
3
3
ground state geometry optimizations through the
COSMO model [58]. The wavelengths of the
electronic absorption transitions (S 0
/Sn) were
0
calculated either at PM3/CI [56] or PM3/S [59]
levels using the ground state geometries. In the
former case (PM3/CI), the ground and all excited
state configurations, due to excitation within
highest occupied (HOMO)ꢃ
pied (LUMO)ꢂ2 molecular orbitals, were in-
cluded in the CI calculations. In the latter case
PM3/S), however, only the ground and single
excited state configurations, due to excitation
within the HOMOꢃ6 and LUMOꢂ6 molecular
/
3 and lowest unoccu-
/
(
/
/
orbitals, were used [60]. Calculations at the PM3/S
level also provided oscillator strengths [59]. In the
prediction of electronic transitions, solvent effects
were included at the PM3/CI level on the basis of
the COSMO model [58]. The wavelengths of
fluorescence (S 0
/
S ), phosphorescence (T 0
/
S0),
triplet
T transitions (cor-
1
0
1
singletꢁ
/
triplet absorption (S 0
/
T ), tripletꢁ
/
0
1
absorption (T 0
/
T ) and S 0
/
1
2
1
1
responding to the difference between the standard
enthalpies of formation of triplet and singlet
entities) were further predicted at the PM3/CI or
PM3/S level using singlet (S ) or triplet (T )
1
1
geometries. The physicochemical characteristics
of the compounds were extracted either directly
from data files following geometry optimizations
(
HOMO and LUMO energies; dipole moments) or
obtained with the available MOPAC 93 routines
bond orders [61], atomic partial charges [62]). All
(
the characteristics were calculated with respect to
ambient temperature and standard pressure.
.
. .. . .
Fig. 4. Absorption (*
fluorescence (----) spectra of 3 in 1,4-dioxane (a), CH
and CH
/
), fluorescence excitation (
) and
OH (b)
3. Results and discussion
3
3
CN (c), together with theoretically predicted excitation
3.1. Experimental absorption and emission spectra
(
j, ', ) and emission (I, ^, ) transitions in the gaseous
3
phase (b) and CH CN (c). PM3/S, lower values; PM3/CI,
The absorption, fluorescence excitation and
higher values.
fluorescence spectra of the compounds investi-
gated are presented in Figs. 2ꢁ7, together with
the theoretically predicted absorption and fluores-
calculated and verified for positive definiteness in
/
order to assess whether or not the structures were

548
A. Bou z˙ yk et al. / Spectrochimica Acta Part A 59 (2003) 543ꢁ558
/
researchers [3ꢁ7,16,18,20,22]. The bands in the
/
fluorescence excitation spectra are situated in the
same wavelength region as those in the corre-
sponding absorption spectra. However, the fluo-
rescence excitation spectra sometimes display a
more intricate structure than the corresponding
absorption spectra, e.g. in the case of 1, 5 or 6.
Furthermore, the maxima in the absorption and
fluorescence excitation spectra of 4 appear at
noticeably different wavelengths, which suggests
that the solvation of molecules in the S state may
0
differ from that in the relaxed S state.
1
Analysis of the spectra recorded in three sol-
vents of different polarities, and of the ability of 9-
acridinones to participate in H-bonding and
electron-donorꢁacceptor interactions, revealed a
/
number of regularities. To begin with, the absorp-
tion, fluorescence excitation and fluorescence
bands always appeared at the highest wavelengths
when the spectra were recorded in methanol and at
the lowest wavelengths when measured in 1,4-
dioxane. The corresponding bands in acetonitrile,
which has the highest dielectric constant of the
solvents used, lie in between the other two.
Another feature is that the bands appearing
around 300 nm always exhibit the highest intensity
in the spectra recorded in 1,4-dioxane. A further
regularity is that the spectra measured in methanol
always contain fewer bands than those recorded in
1,4-dioxane or acetonitrile. These findings appear
to indicate that 9-acridinones interact more readily
with methanol molecules to form H-bonded com-
plexes such as those postulated by Kokubun [6].
3.2. Theoretical versus experimental electronic
absorption and emission transitions
To facilitate our interpretation of the spectra we
calculated the wavelengths of the electronic transi-
tions in 9-acridinones at the level of semi-empirical
PM3/CI and PM3/S methods; the results are
.
. .. . .
Fig. 5. Absorption (*
fluorescence (----) spectra of 4 in 1,4-dioxane (a), CH
and CH
/
), fluorescence excitation (
) and
OH (b)
3
presented in Figs. 2ꢁ7 and Table 1. The wave-
/
3
CN (c), together with theoretically predicted excitation
lengths predicted by both methods for absorption
transitions are always lower than those corre-
sponding to the band maxima in the experimental
spectra. For fluorescence, the theoretically pre-
dicted wavelengths of the emission transitions are
also somewhat lower than the maxima of the
(
j, ', ) and emission (I, ^, ) transitions in the gaseous
3
phase (b) and CH CN (c). PM3/S, lower values; PM3/CI,
higher values.
cence transitions. In general, our characteristics
compare very well with those obtained by other

A. Bou z˙ yk et al. / Spectrochimica Acta Part A 59 (2003) 543ꢁ
/558
549
These findings suggest that the wavelengths of
theoretically predicted transitions would better fit
the experimental spectra if they were scaled, i.e.
multiplied by certain factors. Such scaling factors
for absorption transitions can be obtained by
averaging the ratios of the wavelengths of long-
wavelength bands in absorption (fluorescence
excitation) spectra to those of the corresponding
electronic transitions*both determined by us. In
/
the case of absorption transition in CH CN, the
3
respective scaling factors are 1.059 and 1.099 for
data originating from the PM3/CI and PM3/S
methods. The theoretically predicted wavelengths
of T 0
/
T transitions compare very well with the
2
1
experimentally determined ones in the case of 1
and 5, while for 2 the theoretically predicted
wavelengths are somewhat lower than the empiri-
cal ones. The wavelengths of hypothetical S 0
/
T1
0
transitions and the energy gap between the S and
T states, given in Table 1, complete the informa-
1
1
tion obtained by theoretical methods. Despite a
certain inconsistency in the results, both theore-
tical methods provide quite good predictions of
the electronic transition energies in 9-acridinones
and facilitate the interpretation of experimental
spectra.
3.3. Structure of electronically excited versus
ground state molecules
The structures of the compounds investigated
Fig. 1) in the ground (S ) and electronically
(
excited (S , T ) states are presented in Fig. 8,
0
1
1
while Table 2 sets out those structural parameters
that change most markedly following the electro-
nic excitation of 9-acridinones. As can be seen,
excitation to the S state increases the symmetry of
1
1
excitation to the T state lowers the symmetry of
and lowers the symmetry of 2 and 6, while
1
only 2. In other cases, electronic excitation does
not affect the symmetry. According to the results
of theoretical calculations, 9(10H)-acridinone is
non-planar in the S and T states but planar in the
S1 state. It is predicted that the other 9-acridinones
investigated here are non-planar in all three
.
. .. . .
Fig. 6. Absorption (*
fluorescence (----) spectra of 5 in 1,4-dioxane (a), CH
and CH
/
), fluorescence excitation (
) and
OH (b)
3
3
CN (c), together with theoretically predicted excitation
0
1
(
j, ', ) and emission (I, ^, ) transitions in the gaseous
phase (b) and CH CN (c). PM3/S, lower values; PM3/CI,
3
higher values.
electronic states. The Cꢀ
/
C bond lengths of the
short-wavelength bands in the spectra, while in the
case of phosphorescence the trend is reversed.
lateral benzene rings in 9-acridinones (C C /
(1) (2)
C C ) do not change substantially during elec-
(7) (8)

550
A. Bou z˙ yk et al. / Spectrochimica Acta Part A 59 (2003) 543ꢁ558
/
applies to the Nꢀ
/
C bonds of the central ring
/N (13)). It is interesting, however,
(N
C
C
(
10) (12) (10)
that transformation of 9-acridinones from the S0
to the S or T states alters the lengths of C C /
C C and N(10)C(12)/N(10)C(13) bonds in 1, 2, 5
1
1
(1) (2)
(7) (8)
and 6. The lengths of the C O
(
after excitation from the S to the S (more) or T
bond increase
and the bond orders correspondingly decrease)
(9) (15)
0
1
1
(
less) states. An exception is the S 0
/
T transition
1
0
in 4, during which the length of the C O
bond
(9) (15)
is reduced; the bond order increases correspond-
ingly. Neither the N(10), C(9) and O(15), nor the C(9),
N(10) and A(16) atoms are ever linear: electronic
excitation alters the form of this non-linearity. The
values of the dihedral angles indicate that the
lateral benzene rings of 9-acridinones are only
slightly non-planar in the ground and excited
states. The central rings of the compounds are
non-planar to a much greater degree, and this non-
planarity changes as a result of electronic excita-
tion. The considerable influence of solvents on the
structure of the 9-acridinone ring system should
also be noted: polar solvents (CH OH, CH CN)
3
3
cause the central ring in the ground electronic state
to flatten.
3.4. Properties of electronically excited versus
ground state molecules
Basic thermodynamic (Df,298H8, 298S8) and
physicochemical (HOMO and LUMO energies,
dipole moments) characteristics of 9-acridinones in
the ground (S ) and excited (S , T ) states are given
0
1
1
in Table 3. The standard enthalpies of formation
of gaseous 9-acridinones are all positive: the lowest
is for molecules in the S state and the highest for
0
those in the S state. Df,298H8 values for com-
1
pounds in the T state lie between the other two.
1
Like standard enthalpies of formation, entropies
are characteristic features of 9-acridinones, rising
as the molecular masses of the compounds do so.
In the case of 9(10H)-acridinone, the value of
.
. .. . .
Fig. 7. Absorption (*
fluorescence (----) spectra of 6 in 1,4-dioxane (a), CH
and CH
/
), fluorescence excitation (
) and
OH (b)
3
3
CN (c), together with theoretically predicted excitation
2
98S8 is highest when the molecules are in the S
0
(
j, ', ) and emission (I, ^, ) transitions in the gaseous
phase (b) and CH CN (c). PM3/S, lower values; PM3/CI,
3
state, lower when they are in the S state, and
1
lowest when they are in the T state.
1
higher values.
According to Koopman’s theorem, the negative
energies of LUMO and HOMO (Table 3), respec-
tively, approximate the electron affinity and the
tronic excitation: inspection of the bond order
values makes this immediately apparent. The same

A. Bou z˙ yk et al. / Spectrochimica Acta Part A 59 (2003) 543ꢁ
/558
551
Table 1
Singletꢁ
singletꢁtriplet (S
/
triplet (S
0
0
/
T
1
) and tripletꢁ
) energy gaps in 9-acridinones (nm)
/
triplet (T
1
0
/
T
2
) absorption transitions, singletꢁ
/
singlet (S
1
0/S
0
) phosphorescence transitions and
/
1
0T
/
1
Compound
Method
Solvent
Transition (energy gap) Refs.
S
0
0/T
1
T
1
0/T
2
S
1
0/S
0
S
1
0T
1
/
1
Experimental
Ethanol
Ethanol (77 K)
Methylcyclohexane/
575
[41]
[20,22]
[20]
475
491
2
CH
-methylbutane (77 K)
PM3/CI
3
CN
CN
448
99
477
572
573
561
565
621
908
4
PM3/S
CH
3
2
Experimental
Cyclohexane
,4-Dioxane
Benzene
640
625
630
[42]
[42]
1
[17]
[42]
6
40
CHCl
-Propanol
Acetone
3
623
590
615
582
610
570
[42]
[17]
2
[42]
CH
CH
3
OH
CN
[42]
[42]
3
H
Ethanol (77 K)
2
Oꢂ
/
ethanol
[17]
[20,22]
[20]
475
485
Methylcyclohexane/
2
-methylbutane (77 K)
CH CN
PM3/CI
3
451
94
580
581
565
573
611
926
959
992
4
PM3/S
CH
3
3
CN
CN
478
3
4
5
PM3/CI
CH
456
580
583
566
574
644
499
483
PM3/S
CH
3
3
CN
CN
PM3/CI
CH
457
4
558
549
553
541
613
82
PM3/S
CH
3
CN
494
Experimental
Ethanol
Ethanol (77 K)
580
[22,26]
[22]
475
557
562
605
PM3/CI
CH
3
CN
CN
500
4
569
570
915
53
PM3/S
CH
3
478
6
Experimental
Ethanol (77 K)
Ethanol (72 K)
Methylcyclohexane/
471
475
489
[20]
[22]
[20]
2
CH
-methylbutane (77 K)
PM3/CI
PM3/S
3
CN
414
4
516
504
513
504
547
926
36
CH
3
CN
465
first ionization potential of a molecule [64]. The
ionization potentials (in eV) of 9(10H)-acridinone
9(10-phenyl)-acridinone (7.46 [65]) are on average
0.974 eV lower than negative HOMO energies.
This value can thus be used to correct the
ionization potentials of 9-acridinones in the
(7.60 [65] or 7.69 [66]), 9(10-methyl)-acridinone
7.53 [65]), 9(10-ethyl)-acridinone (7.49 [65]) and
(

Table 2
Structural characteristics of 9-acridinones in the ground (S
theory
0
) and excited (S
1
, T
1 0 1 1
) electronic states predicted at the PM3 (PM3-COSMO) (S ) or PM3/CI (S , T ) levels of
a
Compound Medium Bond lengths a
a
Bond orders
Angle
Dihedral angles
(
Fig. 1)
C
C
(1)
(7)
C
C
(2)
/
C
(9)
O
(15)
N
N
(10)
C
C
(12)
/
C
C
(1)
(7)
C
C
(2)
/
C
(9)
O
(15)
N
N
(10)
C
C
(12)
/
N
(10)
C
(9)
O
A
(15)
/
C
C
(3)
C
C
(2)
(7)
C
C
(1)
C
C
(11)
(14)
/
C
C
(11)
C
(12)
N
(10)
C
C
(13)
(14)
/
C
C
(12)
C
C
(11)
C
(9)
C
C
(14)
/
(8)
(10)
(13)
(8)
(10)
(13)
C
(9)
N
(10)
(16)
(6)
(8)
(12)
N
(10)
C
(13)
(11)
(9)
C
(14)
(13)
S
0
state
1
Gaseous 1.39
,4-Di- 1.39
oxane
1.22
1.23
1.42
1.42
1.46
1.46
1.86
1.85
1.09
1.09
170/170
170/161
0
0
ꢃ
/
19/19
10/ꢃ
/
10
1
ꢃ19/19
/
10/ꢃ10
/
CH
CH
3
OH 1.38
CN 1.38
1.24
1.24
1.41
1.41
1.48
1.48
1.83
1.83
1.10
1.10
173/165
173/165
0
0
ꢃ
/
15/15
6/ꢃ
/
6
3
ꢃ15/15
/
6/ꢃ
/
6
2
3
Gaseous 1.39
,4-Di- 1.38
oxane
1.22
1.23
1.43
1.43
1.46
1.46
1.85
1.85
1.07
1.07
177/160
177/161
0
0
ꢃ
/
9/9
2/ꢃ
/
2
1
ꢃ
/
9/9
2/ꢃ
/
2
CH
CH
3
OH 1.38
CN 1.38
1.24
1.24
1.42
1.42
1.48
1.48
1.83
1.83
1.08
1.08
178/164
178/164
0
0
ꢃ
/
7/7
0
0
3
ꢃ
/
7/7
Gaseous 1.39
1.22
1.23
1.24
1.24
1.43
1.43
1.42
1.42
1.44/
1
1.85
1.85
1.83
1.83
1.07
1.07
177/160
177/160
178/164
178/164
0
0
0
0
ꢃ
/
9/9
9/9
7/7
7/7
2/ꢃ
1/ꢃ
1/ꢃ
1/ꢃ
/
2
.46
1
,4-Di- 1.39/
oxane 1.38
OH 1.39/
.38
CN 1.39/
.38
1.45/
1.46
1.46/
1.48
1.46/
1.48
ꢃ/
/
1
CH
3
3
1.08/1.09
1.08/1.09
ꢃ/
/
1
1
CH
ꢃ/
/
1
1
4
Gaseous 1.40/
.39
,4-Di- 1.40/
oxane 1.39
OH 1.40/
.38
CN 1.40/
.38
1.22
1.23
1.24
1.24
1.42/1.43
1.41/1.43
1.40/1.43
1.40/1.43
1.40/
1.46
1.40/
1.46
1.41/
1.47
1.41/
1.47
1.86
1.86
1.84
1.84
1.13/1.06
1.14/1.06
1.18/1.07
1.17/1.07
177/165
179/166
178/173
179/173
0
0
0
0
ꢃ
/
8/7
6/5
1/2
1/1
1/ꢃ2
/
1
1
ꢃ/
0
CH
3
3
ꢃ/
3/ꢃ
/
3
1
CH
ꢃ/
2/ꢃ
/
2
1
5
6
Gaseous 1.39
,4-Di- 1.38
oxane
1.22
1.23
1.43
1.43
1.46
1.47
1.85
1.85
1.07
1.07
178/157
178/158
0
0
3/ꢃ
/
3
4/ꢃ
/
4
1
3/ꢃ
/3
5/ꢃ
/
5
CH
CH
3
OH 1.38
CN 1.38
1.24
1.24
1.42
1.42
1.48
1.48
1.83
1.83
1.09
1.08
177/162
178/163
0
0
2/ꢃ
/2
5/ꢃ
/
5
3
3/ꢃ
/3
4/ꢃ
/
4
Gaseous 1.39
1.22
1.43
1.46
1.85
1.07
173/167
0
ꢃ
/
14/14
6/ꢃ6
/

Table 2 (Continued)
a
a
Compound Medium Bond lengths a
Fig. 1)
Bond orders
Angle
Dihedral angles
(
C
C
(1)
(7)
C
C
(2)
/
C
(9)
O
(15)
N
N
(10)
C
C
(12)
/
C
C
(1)
(7)
C
C
(2)
/
C
(9)
O
(15)
N
N
(10)
C
C
(12)
/
N
(10)
C
(9)
O
A
(15)
/
C
C
(3)
C
C
(2)
(7)
C
C
(1)
C
C
(11)
(14)
/
C
C
(11)
C
(12)
N
(10)
C
C
(13)
(14)
/
C
C
(12)
C
C
(11)
C
(9)
C
C
(14)
/
(8)
(10)
(13)
(8)
(10)
(13)
C
(9)
N
(10)
(16)
(6)
(8)
(12)
N
(10)
C
(13)
(11)
(9)
C
(14)
(13)
1,4-Di- 1.38
oxane
1.23
1.43
1.47
1.84
1.07
173/169
0
ꢃ
/
14/14
7/ꢃ
/
7
CH
CH
3
OH 1.38
CN 1.38
1.24
1.24
1.41
1.41
1.48
1.48
1.82
1.82
1.10
1.10
179
179
0
0
ꢃ
/
2/2
1/ꢃ
/
1
3
ꢃ
/
1/1
0
0
S
1
state
1
Gaseous 1.39/
.38
1.23
1.23
1.23
1.23
1.23
1.23
1.39/1.42
1.39/1.44
1.39/1.44
1.47/1.39
1.43/1.40
1.43/1.39
1.34/
1.52
1.73
1.72
1.71
1.81
1.71
1.72
1.25/1.18
1.22/1.13
1.24/1.12
1.08/1.28
1.14/1.22
1.14/1.22
177/180
172/166
172/164
170/157
172/170
175/170
0
0
1
2
3
4
5
6
Gaseous 1.40/
.38
1.34/
1.52
1/ꢃ
1/ꢃ
0/ꢃ
/
1
ꢃ
/
9/17
11/ꢃ
/3
1
Gaseous 1.40/
.38
1.30/
1.53
/1
ꢃ
/
9/17
10/ꢃ
/2
1
Gaseous 1.38
1.39/
1
/1
ꢃ
/
25/11
12/12
14/5
1/ꢃ
/
14
9
.38
Gaseous 1.38/
1.52/
1.34
1
ꢃ/
9/ꢃ
/
1
.40
Gaseous 1.38/
.40
1.51/
1.34
1/ꢃ
/1
ꢃ/
ꢃ
/
2/ꢃ7
/
1
T
1
state
1
Gaseous 1.38/
.37
1.23
1.23
1.23
1.22
1.23
1.23
1.44/1.38
1.45/1.39
1.45/1.39
1.39/1.45
1.39/1.45
1.39/1.45
1.40/
1.52
1.75
1.73
1.73
1.88
1.73
1.73
1.10/1.22
1.09/1.19
1.09/1.19
1.19/1.11
1.20/1.08
1.19/1.09
173/165
177/159
177/158
170/154
175/159
178/164
0
ꢃ
/
15/15
7/ꢃ
3/ꢃ
3/0
/
7
1
2
3
4
5
6
Gaseous 1.38/
.37
1.41/
1.54
0/1
1
3/ꢃ
/7
ꢃ
/
/1
1
Gaseous 1.39/
.37
1.39/
1.54
4/ꢃ
/7
ꢃ/
1
Gaseous 1.43/
.39
1.18/
1.40
1/0
1
ꢃ
/
10/10
12/ꢃ
8/ꢃ
3/ꢃ
/
12
1
Gaseous 1.37/
.38
1.54/
1.40
ꢃ
/
5/7
/
6
1
Gaseous 1.37/
.38
1.53/
1.40
0
0/2
/
1
1
˚
Bond lengths are in A and bond angles in degrees; bond orders originate from rotationally invariant bond order analysis [61].
a
0
The values for the gaseous medium (S state) were taken from our previous work [63].

554
A. Bou z˙ yk et al. / Spectrochimica Acta Part A 59 (2003) 543ꢁ558
/
ground electronic state. The HOMO energies of 9-
acridinones in the S and T states are comparable,
but much higher than those in the S state. This
LUMO energies are very reliable. These energies
of gaseous 9-acridinones are quite similar in the
ground and excited electronic states; however,
these quantities are lower in polar solvents.
Dipole moments (m) are a reflection of non-
uniform negative charge distribution within mole-
cules. The dipole moments (in D), measured in
benzene, of 9(10H)-acridinone (6.0 [20]), 9(10-
methyl)-acridinone (5.3 [20] or 5.39 [67]), and
9(10-phenyl)-acridinone (5.4 [20]) compare reason-
1
1
0
means that the ionization of such molecules would
require much less energy. The negative LUMO
energies are unexpected: this suggests that follow-
ing electron attachment, 9-acridinones form stable
negative ions in both ground (S ) and excited (S ,
0
1
T ) states. As this characteristic was not confirmed
1
experimentally, we do not think that the predicted
Fig. 8. PM3 (the ground (S ) state) and PM3/CI (the excited (S
0
1
, T
1
) electronic states) optimized geometries of 9-acridinones (the point
group symmetry is indicated in parentheses following the numbering of molecules).

A. Bou z˙ yk et al. / Spectrochimica Acta Part A 59 (2003) 543ꢁ
/558
555
Table 3
Physicochemical characteristics of 9-acridinones in the ground (S
0
1 1
) and excited (S , T ) electronic states predicted at the PM3 (PM3-
COSMO) (S ) or PM3/CI (S
0
1
, T
1
) levels of theory
a
a
Compound
Medium
D
f,298H8
298S8
Energy
m
Relative atomic charge
(
Fig. 1)
HOMO
LUMO
C
(9)
N
(10)
O
(15)
S
0
state
1
Gaseous
57
39
11
11
428
459
505
527
460
536
ꢃ
/
8.5
8.6
8.6
8.6
ꢃ
/
0.6
0.7
0.9
0.9
3.8
0.39
0.43
0.47
0.47
0.18
0.18
0.22
0.22
ꢃ
/
0.34
0.40
0.51
0.51
1
,4-Dioxane
ꢃ
/
ꢃ
/
4.7
7.0
7.0
ꢃ
/
CH
CH
3
OH
CN
ꢃ
/
ꢃ
/
ꢃ
/
3
ꢃ/
ꢃ/
ꢃ/
2
3
4
5
6
Gaseous
,4-Dioxane
65
48
22
22
ꢃ
/
8.4
8.5
8.6
8.6
ꢃ
/
0.6
0.7
1.0
1.0
4.0
4.9
7.0
7.1
0.39
0.42
0.47
0.47
0.15
0.16
0.19
0.19
ꢃ
/
0.34
0.40
0.51
0.51
1
ꢃ
/
ꢃ
/
ꢃ
/
CH
CH
3
OH
CN
ꢃ
/
ꢃ
/
ꢃ
/
3
ꢃ/
ꢃ/
ꢃ/
Gaseous
,4-Dioxane
26
9
ꢃ
/
8.4
8.4
8.5
8.5
ꢃ
/
0.6
0.7
1.0
1.0
3.9
4.8
6.9
7.0
0.39
0.42
0.47
0.47
0.16
0.16
0.19
0.19
ꢃ
/
0.34
0.40
0.51
0.51
1
ꢃ
/
ꢃ
/
ꢃ
/
CH
CH
3
OH
CN
ꢃ17
/
ꢃ
/
ꢃ
/
ꢃ
/
3
ꢃ17
/
ꢃ/
ꢃ/
ꢃ/
Gaseous
,4-Dioxane
27
23
96
97
ꢃ
/
9.0
9.0
8.7
8.7
ꢃ
/
1.3
1.3
1.3
1.3
8.9
10.5
13.8
13.9
0.39
0.42
0.48
0.48
0.18
0.19
0.25
0.25
ꢃ
/
0.33
0.39
0.50
0.50
1
ꢃ
ꢃ
ꢃ
/
ꢃ
/
ꢃ
/
ꢃ
/
CH
CH
3
OH
CN
/
ꢃ
/
ꢃ
/
ꢃ
/
3
/
ꢃ/
ꢃ/
ꢃ/
Gaseous
,4-Dioxane
40
23
2
ꢃ
/
8.4
8.5
8.6
8.6
ꢃ
/
0.6
0.7
1.0
1.0
4.1
5.0
7.1
7.1
0.39
0.42
0.47
0.47
0.14
0.15
0.17
0.17
ꢃ
/
0.34
0.40
0.51
0.51
1
ꢃ
/
ꢃ
/
ꢃ
/
CH
CH
3
OH
CN
ꢃ
/
ꢃ
/
ꢃ
/
3
ꢃ
/3
ꢃ/
ꢃ/
ꢃ/
Gaseous
,4-Dioxane
200
182
156
155
ꢃ
/
8.4
8.5
8.5
8.5
ꢃ
/
0.5
0.7
1.0
1.0
4.7
5.6
7.9
7.9
0.39
0.42
0.47
0.47
0.22
0.23
0.28
0.27
ꢃ
/
0.34
0.40
0.51
0.51
1
ꢃ
/
ꢃ
/
ꢃ
/
CH
CH
3
OH
CN
ꢃ
/
ꢃ
/
ꢃ
/
3
ꢃ/
ꢃ/
ꢃ/
S
1
state
1
Gaseous
Gaseous
Gaseous
Gaseous
Gaseous
Gaseous
431
434
391
377
415
570
401
ꢃ
/
2.8
2.7
2.6
3.5
2.7
2.7
ꢃ
/
0.4
0.4
0.4
1.1
0.4
0.8
4.0
4.3
0.32
0.31
0.31
0.36
0.31
0.31
0.51
0.47
0.46
0.49
0.46
0.56
ꢃ
/
0.32
0.32
0.32
0.28
0.32
0.32
2
3
4
5
6
ꢃ/
ꢃ/
ꢃ/
ꢃ/
ꢃ/
4.2
ꢃ/
ꢃ/
ꢃ/
10.0
4.5
ꢃ/
ꢃ/
ꢃ/
ꢃ/
ꢃ/
ꢃ/
4.5
ꢃ/
T
1
state
1
Gaseous
Gaseous
Gaseous
Gaseous
Gaseous
Gaseous
299
304
266
257
284
440
394
ꢃ
/
2.9
2.9
2.8
3.6
2.8
2.8
ꢃ
/
0.4
0.4
0.4
1.1
0.4
0.6
4.8
5.5
0.32
0.31
0.30
0.36
0.30
0.31
0.46
0.44
0.45
0.49
0.44
0.51
ꢃ
/
0.34
0.35
0.35
0.29
0.35
0.35
2
3
4
5
6
ꢃ/
ꢃ/
ꢃ/
ꢃ/
ꢃ/
5.5
ꢃ/
ꢃ/
ꢃ/
12.2
5.6
ꢃ/
ꢃ/
ꢃ/
ꢃ/
ꢃ/
ꢃ/
6.3
ꢃ/
D
f,298H8 (kJ molꢃ1) denotes the standard enthalpy of formation; 298S8 (J molꢃ1 ꢃ1) is the entropy; HOMO and LUMO (eV)
K
ꢃ30
indicate the energies of the HOMO and LUMO; m, in Debyes (1 Debyeꢄ
/
3.336ꢅ/10
Cm), is the dipole moment; relative atomic
charges are derived from Mulliken population analysis [62].
a
0
Values for the gaseous medium (S state) were taken from our previous work [63].
ably well with those predicted at the PM3 level in
,4-dioxane. Compound 4 can be regarded as
highly polar, since its dipole moment is relatively
high; this quantity is smaller in the less-polar 9-
acridinones, i.e. 1, 2, 3, 5 and 6. The theoretical
value of a dipole moment depends substantially on
1

556
A. Bou z˙ yk et al. / Spectrochimica Acta Part A 59 (2003) 543ꢁ558
/
the solvent in which it is measured and increases as
its polarity does so. On comparing predicted m
values of gaseous 9-acridinones, the following
indicate that the process is accompanied by
changes in electron density distribution. This effect
is demonstrated directly in Fig. 9 and in Table 3,
where the relative atomic charges on selected
atoms are given. Theory predicts that the principal
changes in electron density accompanying the
sequence can be noted: m (T )ꢀ
/
m (S )ꢀ
/
m (S0).
Abdullah and Kemp reported a value of m (T ) for
1
1
n
9
(10-methyl)-acridinone equal to 5.85 D [42],
which corresponds quite well to the value of 5.46
D predicted at the PM3/CI level. On the other
hand, the value of m of 7.287 D for this compound
S00
/
S and T 0
/
S0 transitions occur within the
1
1
heterocyclic N atom and the adjacent C atom (Fig.
9). Furthermore, changes in electron density occur
in one of the lateral benzene rings containing this
C atom. The keto group, and the substituents in
positions 2 and 10, participate only slightly in the
electronic transitions within the ground and ex-
cited states. Atomic charges are a quantitative
reflection of electron density changes; these values
in the S state reported by Koutek [67] is much
1
higher than that predicted at the PM3/CI level and
seems to have been overestimated. Dipole mo-
ments may be considered a measure of the ability
of 9-acridinones in various electronic states to
participate in non-specific interactions with other
molecules. The data in Table 3 can thus serve as a
convenient source of information enabling the
features of such interactions to be predicted.
for C , N and O(15) atoms are given in Table 3.
(10)
(9)
Theory predicts that there is always a negative
charge deficiency at the C(9) and N(10) atoms and
an excess of negative charge at the O(15) atom
(oxygen is the most electronegative of the elements
present in 9-acridinones). The atomic charges
change slightly at the C(9) and O(15) atoms and
substantially at the N(10) atom following electronic
excitation, which is demonstrated directly in Fig.
3.5. Electron density changes accompanying
electronic excitation
The theoretically predicted changes of dipole
moments caused by electronic excitation (Table 3)
Fig. 9. Changes in electron densities accompanying S
and filled circles the increase of the electron density at a given atom; the area of the circles is proportional to the absolute value of the
0
0/S
1
and T
1
0
0/S transitions in 9-acridones. Empty circles indicate the decrease
electron density change at a given atom.

A. Bou z˙ yk et al. / Spectrochimica Acta Part A 59 (2003) 543ꢁ
/558
557
9
(
. Without doubt, the electron density changes
Fig. 9) indicate that the electronic transitions
must be accompanied by dipole moment
changes*an effect predicted by theory (Table 3)
and proven experimentally [42].
(KBN) under grant 3 T09A 083 16 (contract No.
1177/T09/99/16).
/
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