12-Hydroxy-1-azaperyleneâLimiting Case of the ... - ACS Publications

Article pubs.acs.org/JPCA

12-Hydroxy-1-azaperyleneLimiting Case of the ESIPT System: Enol−Keto Tautomerization in S0 and S1 States Irena Deperasińska,† Daniel T. Gryko,‡ Elena Karpiuk,† Bolesław Kozankiewicz,*,† Artur Makarewicz,† and Joanna Piechowska‡ †

Institute of Physics of the Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw, Poland Institute of Organic Chemistry of the Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland

‡

S Supporting Information *

ABSTRACT: Absorption, fluorescence, and fluorescence excitation spectra of 12-hydroxy1-azaperylene (HAP) and 1-azaperylene were studied in n-alkane matrices at 5 K. Two stable tautomers of HAP, each of them in n-nonane embedded in two sites, were identified and attributed to the enol and keto forms. Theoretical calculations of the energy and vibrational structure of the spectra suggest that tautomer A, with the (0, 0) transition energy at 18 980 ± 10 cm−1 (and 19 060 ± 10 cm−1 in the high energy site), should be identified as the keto form, whereas tautomer B, with the (0, 0) energy at 19 200 ± 20 cm−1 (19 290 ± 20 cm−1), as the enol form. Observation of absorption and fluorescence of both tautomeric forms and lack of large Stokes shift of fluorescence of the keto form classify HAP as the limiting case of the excited-state intramolecular proton transfer system.

I. INTRODUCTION The excited-state intramolecular proton transfer (ESIPT) is one of the most important photochemical reactions in organic systems and applies to many fields of chemistry and molecular biology.1 Aromatic compounds displaying ESIPT, such as benzoxazoles,2 flavones,3 imidazoles,4 or anthraquinones,5 have found many important applications as photoswitches,6 fluorescent sensors,7 laser dyes,8 fluorescence recordings,9 ultraviolet stabilizers,10 proton and metal ion sensors,11 and probes for solvation dynamic12 and biological environments13 and recently in organic light emitting devices.14 It is widely accepted that the fingerprint of ESIPT is a large Stokes shifted fluorescence which manifests significant structure and electronic configuration changes in the electronically excited state of the ESIPT molecule. Most ESIPT molecules contain both a pyridine-type nitrogen atom and a phenolic hydroxyl group.15 In the ground S0 state the molecule has the enol form, with the hydroxyl proton occupying the hydrogen bonding configuration. Promotion of the molecule to the S1 excited state is followed by the transfer of this proton (without a barrier) to the basic nitrogen atom, thus creating the keto form. Therefore, observation of only one form (enol) in the absorption spectrum and another form (keto) in the fluorescence spectrum is characteristic for the ESIPT systems. In spite of a vast amount of research and increasing importance of ESIPT, there are still many important questions worth exploring, like influence of the structure and extension of π-conjugated systems. One of the © 2012 American Chemical Society

most prominent ESIPT systems that undergoes an ultrafast proton transfer free of solvent perturbations is 10hydroxybenzo[h]quinoline (10-HBQ).15 A preliminary spectroscopic study of newly synthesized 12-hydroxy-1-azaperylene (HAP), which incorporates the 10-HBQ moiety and thus was expected to belong to the group of ESIPT molecules, led to a surprising observation. In room temperature solutions no bathochromically shifted emission was observed, presumably owing to the lack of a considerable energy difference between excited states of the hypothetical enol and keto forms.16 The aim of the current study is to shed light upon this intriguing compound and to try to explain its photophysical behavior. Information about structural properties of molecules can be derived (with the use of appropriate theoretical methods) from an analysis of the vibronic pattern of absorption and fluorescence spectra.17 Convenient media for such studies are low temperature n-alkane Shpol’skii matrices where the spectra of embedded organic molecules are frequently composed of vibrational quasi-lines.18 In the present contribution, we study absorption, fluorescence, and fluorescence excitation spectra of HAP in the Shpol’skii matrices of n-heptane and n-nonane at 5 K. As a preliminary step leading to the study of the HAP system, we Received: October 27, 2011 Revised: February 8, 2012 Published: February 8, 2012 2109

dx.doi.org/10.1021/jp2103353 | J. Phys. Chem. A 2012, 116, 2109−2116

The Journal of Physical Chemistry A

Article

extended our investigation to novel 1-azaperylene (AP) in a Shpol’skii matrix of n-heptane. The spectra of AP, which can be considered as an intermediate between perylene and HAP, were previously examined only in solution at room temperature. 16 The molecular structures of both investigated compounds are shown in Figure 1.

Figure 1. Molecular structures of 1-azaperylene (AP) and the enol form of 12-hydroxy-1-azaperylene (HAP).

II. EXPERIMENTAL AND COMPUTATIONAL METHODS AP and HAP were prepared using the methods described in the literature.16 Spectroscopic studies were performed with AP and HAP in n-heptane (Uvasol, Merck) and n-nonane (Sigma-Aldrich), concentration 10−5−10−4 M. Liquid samples were bubbled with argon to remove oxygen and subsequently quickly frozen (in liquid nitrogen, at 77 K) before being transferred to a liquid helium optical cryostat. Single-beam absorption spectra were measured with the aid of a homemade cuvette in which two quartz windows were separated by a 1.5 mm Teflon ring. The light from a xenon lamp, which was transmitted through the sample of a solid solution, was analyzed with a McPherson 207 monochromator and detected with an EMI9659 photomultiplier operating in photon counting mode. Fluorescence and fluorescence excitation spectra were measured at 5 K with the photon sampling technique. The excitation source was a Lambda Physics FL1001 dye laser (lasing media were either Coumarin 47, for the 440−480 nm range, or Coumarin 307, for the 480−530 nm range) pumped by an LPX100 excimer laser. Fluorescence photons were dispersed with a McPherson 207 monochromator and detected with an EMI9659 photomultiplier (prepared for pulse mode) and a Stanford Research SR250 boxcar averager. Optimization of the molecular geometry in the electronic ground S0 and excited S1 states and calculations of the energy and the oscillator strengths of electronic transitions were carried out using DFT (B3LYP and TD B3LYP methods with the 6-31G(d,p) basis). Energies of the transition state (energy barriers) were obtained by the QST2 method. Solvent effect (n-nonane and acetonitrile) was calculated within the PCM model. All the calculations were done with the aid of a Gaussian 09 package.19 The Franck−Condon factors were calculated as an approximation of a displaced oscillator.20

Figure 2. Fluorescence (νexc = 22 420 cm−1) and the low energy portion of the fluorescence excitation (νobs = 21 710 cm−1) spectra of AP in n-heptane at 5 K. The calculated vibrational structure is presented in the form of vertical lines at the bottom of the figure.

broad (and relatively strong) phonon side bands. We also observed the higher energy AP site (which had the (0, 0) line at 22 269 cm−1) in an n-heptane matrix, but in the present work we concentrated only on the main site. The vibrational mode frequencies observed in the fluorescence spectrum of AP (Figure 2) are listed in the first column of Table 1. In the third and fourth columns we have provided vibrational frequencies for the parent perylene isolated in Ne matrix21 and in biphenyl and anthracene crystals.22 It is easy to notice similarities in the vibronic patterns of both compounds (perylene and AP). In addition the fluorescence origin is within the energy range expected due to the difference in solvent shift.18 For example, the dominant site of the (0, 0) transition for perylene in an n-nonane matrix appeared at 22 533 cm−1 and in biphenyl and anthracene crystals at 22 457 and 22 263 cm−1, respectively.22,23 The vibrational structure of the electronic spectrum reflects the changes in molecular geometry of the two states taking part in the transition. In the Supporting Information we provide the detailed information concerning optimized bond lengths of the AP molecule in the electronic ground, S0, and excited, S1, states (Figure 1S), as well as frequencies of the normal modes in both electronic states (Table 1S). It can be easily seen that substitution of N atom shortens the bond lengths between this atom and the neighboring C atoms (see the C−C bond lengths on the opposite side of molecule, which remain unchanged by the substitution as compared with perylene). Excitation of AP to its S1 state shortens the central C−C bonds connecting the naphthalene and isoquinoline moieties. The above data were used to calculate the displacement parameters, namely, the projection of the geometry change between the S0 and S1 states onto the normal mode of the S0 state, and the Franck−Condon factors20 for each vibrational mode. The values of the displacement parameters are given in the last column of Table 1S (see Supporting Information), and the Franck−Condon factors, which define the expected vibrational structure, are given at the bottom of Figure 2 in the form

III. RESULTS AND DISCUSSION a. 1-Azaperylene in n-Heptane. The fluorescence spectrum and low energy portion of the fluorescence excitation spectrum of AP in its main site in an n-heptane matrix at 5 K are presented in Figure 2. The maximum of the zero-phonon line of the (0, 0) transition is at 22 044 cm−1 in the fluorescence spectrum and at 22 076 cm−1 in the fluorescence excitation spectrum. Narrow zero-phonon lines are accompanied by 2110



Article

Table 1. Comparison of Fluorescence Spectra Vibrational Frequencies (in cm−1) for AP and Perylene: Experimental Frequencies of AP in an n-Heptane Matrix (First Column), Calculated Frequencies of the Corresponding Normal Modes (Second Column), and Vibrational Frequencies for Perylene Isolated in Ne Matrix and in Biphenyl and Anthracene Crystals (Third and Fourth Columns) AP in n-heptane matrix experiment

calculation

345 419 529 697 769 799 880 951 987 1041 1152 1179 1280 1360 1551 1576 1627 1706 1781 1900 1987 2060 2250 2715 2933

342 419 541 2 × 342 342 + 419 783 342 + 541 941 976 1051 342 + 782 1183 1264 1370 1555 1593 1623 342 + 1370 419 + 1370 342 + 1555 419 + 1555 2 × 342 + 1370 342 + 541 + 1370 2 × 1370 1370 + 1555

perylene isolated in Ne matrix9

biphenyl (anthracene) crystal10

354 427 546

358 (355) 557 (555) 715 (711)

780

Figure 3. Absorption spectrum of HAP in an n-nonane at 5 K. A more detailed view of structured absorption lines at low energy is shown at the top left corner. The fluorescence spectrum obtained with excitation frequency νexc ≈ 26 810 cm−1 (indicated by arrow) is given at the bottom of the figure.

1106

1291 1372

1311 (1304) 1384 (1382)

1581

1584 (1581)

vely narrow lines in this spectrum (maxima at 17 565 and 17 470 cm−1) are fingerprints of isomer A, while the other, broader fluorescence lines (19 150−19 350 and 17 800− 18 050 cm−1) belong to isomer B. The complex structure of the fluorescence spectrum was confirmed by the fact that the relative intensity of lines attributed to isomers A and B depends on the excitation frequency. In addition, the origin line (the highest energy line) of the fluorescence spectrum (Figure 3) is located at higher energy than the lowest energy absorption line. The two, relatively narrow bands in the absorption spectrum at 26 760 and 28 100 cm−1 we attribute to transitions to higher electronic states with large oscillator strength. To resolve the spectra corresponding to the isomers A and B, we used narrow line excitation provided by a dye laser. Results of our experimental study are summarized in Figure 4, where we present selected fluorescence and fluorescence excitation spectra attributed to the isomers A and B of HAP in an n-nonane matrix at 5 K. A characteristic feature of the fluorescence spectrum of isomer A (Figure 4a) is a lack of the (0, 0) origin line and the presence of vibronic lines (fwhm ≈ 30 cm−1) with maxima (in order of decreasing intensity) at 17 565, 17 470, 18 315, 17 230, 18 520, 18 610, and 17 030 cm−1. A lack of the origin line is difficult to explainwe can only propose that it is due to poor Franck−Condon overlap. Isomer A in an n-nonane matrix occupies two sites. The fluorescence excitation spectrum (analogue of absorption spectrum) of the high energy site (observation frequency at νobs = 17 565 cm−1) has a narrow (0, 0) origin line (fwhm ≈ 20 cm−1) at 19 060 cm−1 and vibronic components at 19 115, 19 215, and 19 430 cm−1. The low energy site contributes to the spectrum when νobs = 17 470 cm−1 and its (0, 0) line has a maximum at 18 980 cm−1. Vibronic components of this low energy site (marked by an asterisk) are mixed with lines attributed to the high energy site. Fluorescence excitation (Figure 4a) and absorption (Figure 3) lines of isomer A are sharp in the limited spectral range (below 19 500 cm−1). At higher energies the spectrum of isomer A becomes broader and weaker, and it is difficult to assign peaks to specific isomer. Such a dramatic broadening of the absorption

1740 (1739) 1938 (1937)

of vertical lines. Calculated frequencies of the vibrational normal modes were scaled by a factor of 0.97. Attribution of vibrational modes observed in the fluorescence spectrum of AP are given in the second column of Table 1. Using the data presented in Figure 2 and Table 1 we concluded that in AP, as in the case of perylene, the most important components of the spectrum are lines corresponding to three modes: 345, 529, and 1360 cm−1 (and their combinations). The first two modes correspond to stretchings along the long and short axes of AP molecule (see Figure 2S). The third mode (which is in the plane) corresponds to quasi-symmetric rotation of each external ring of AP between the short and long axes. b. 12-Hydroxy-1-azaperylene in n-Nonane. The absorption spectrum of HAP in an n-nonane matrix at 5 K is provided in Figure 3. It exhibits two main features: relatively narrow lines located between 18 950 and 19 450 cm−1 and several broad bands at higher energies. Such a spectrum suggests the presence of at least two HAP isomers in the sample. The isomers leading to the narrow and broad bands will be designated A and B, respectively. It is worth mentioning that at the majority of frequencies the absorption spectra of isomers A and B coincide, and it was not easy to find an excitation frequency (νexc) which is absorbed selectively by only one of the isomers. At the bottom of Figure 3, we present a typical fluorescence spectrum (obtained for νexc ≈ 26 760 cm−1), which shows contributions from both isomers. The relati2111



Article

absorption lines (see Figure 3) of isomer B have maxima at 19 660, 20 500, 21 800, and 23 150 cm−1. The origin line in the absorption spectrum of isomer B is much weaker compared to the vibronic components (the highest intensity component is located at 20 500 cm−1, ∼1300 cm−1 above the origin energy). This indicates that isomer B undergoes a significant geometrical reorganization when excited from the S0 to the S1 state. According to the above considerations, we determined the (0, 0) transition energy of isomer B to be 19 200 ± 20 cm−1 in its low energy site, and 19 290 ± 20 cm−1 in its high energy site. Our experimental studies prove that HAP has two stable isomers (with (0, 0) transition energies differing by 220−230 cm−1), which in an n-nonane matrix occupy two sites (with (0, 0) transition energies differing by 80−90 cm−1). It seems obvious to expect that the two isomers of HAP should be assigned to the enol and keto forms, where the hydrogen atom is bound either to the oxygen or to the nitrogen atom, respectively. To gain in-depth understanding of the experimental observations, we performed quantum molecular calculations. Over the course of our calculations we have optimized molecular geometries of the enol and keto forms of HAP in both the ground, S0, and excited, S1, electronic states. The optimized bond lengths are given in Table 2S of the Supporting Information, while the data characterizing all calculated vibrational modes of both tautomeric forms are collected in Tables 3S and 4S. The existence of stable enol and keto forms of HAP was also predicted from our calculations performed for isolated (gas phase) HAP, and in n-nonane and acetonitrile solutions. The latter solvent was used in order to control the influence of polarity, as well as to compare our results with previously reported data.16 The energies of both tautomers and their transition energies (which can be considered as energy barriers between them), taken with respect to the energy of the enol form, are given in Table 2. Calculations unambiguously showed

Figure 4. Fluorescence and fluorescence excitation spectra of the A (a) and B (b) isomers of HAP in an n-nonane matrix at 5 K. Frequencies of excitation (fluorescence) and observation (fluorescence excitation) are provided close to the corresponding spectra. Lines attributed to the low energy site are marked by *.

Table 2. Energy Relations between the Enol and Keto Tautomers of HAP in the Electronic Ground, S0, and Lowest Excited Singlet, S1, States and the Energy Barriers between These Two States (Transition States, TS)a

spectrum of isomer A suggests overcrossing the energy barrier (height ∼400 cm−1) leading to another state (or form) of the molecule. The (0, 0) origin of fluorescence of isomer B is composed of two lines, with maxima at 19 200 and 19 290 cm−1 (see Figure 4b). The relative intensity of these two fluorescence lines changed as the frequency of excitation light was varied. We therefore attributed them to two different sites of HAP in an n-nonane matrix (the line corresponding to the lower energy site is indicated by an asterisk). We did not succeed in finding an excitation frequency which led to selective excitation of only one site of the isomer B and which did not also excite fluorescence of isomer A. The origin fluorescence lines of isomer B are accompanied by weakly structured vibronic components located between 17 750 and 18 100 cm−1. The fluorescence excitation lines of isomer B (shown in Figure 4b) are relatively broad (fwhm ≈ 150 cm − 1 ) and contain contributions from both sites. Maxima of these lines (which we attribute to the low energy site) are at 19 200, 19 670, and 20 500 cm−1. In the absorption spectrum presented in Figure 3, the lowest energy origin line attributed to isomer B (which in the fluorescence excitation spectrum was observed at 19 200 cm−1) is hidden under the stronger lines from isomer A. Other

S0 state

gas n-nonane acetonitrile

S1 state

enol form

TS

keto form

(enol form)*

TS

(keto form)*

0 0 0

1095 980 815

410 170 −215

0 0 0

825 790 675

145 −55 −420

a Energies given in cm−1 with respect to the energy of the enol form. Zero-point correction to the energy was introduced.

that for isolated HA, the most stable form in both electronic states is the enol, whereas a polar solvent such as acetonitrile stabilizes the keto form. In an n-nonane solution the enol is the most stable ground state conformation, while in the lowest excited state the keto form predominates. The energy differences between both forms are very small, especially with respect to the uncertainty inherent in the calculations. Nevertheless, it is safe to conclude that HAP is a system characterized by a nearly symmetric doubleminimum potential, especially in the excited S1 state.24 Calculated transition energies and oscillator strengths for the S0 → S1 absorption and S1 → S0 emission are given in Table 3. These values are similar to those obtained for both tautomers 2112



Article

Table 3. Energy (ΔE) and Oscillator Strength (f) of the Transitions between the S0 and S1 States for Both Forms of HAP S0 → S1

gas n-nonane acetonitrile

S1 → S0

enol form

keto form

−1

−1

(enol form)* −1

(keto form)*

ΔE (cm )

f

ΔE (cm )

f

ΔE (cm )

f

ΔE (cm−1)

f

22950 22345 21320

0.33 0.43 0.62

22420 21800 20710

0.28 0.37 0.55

20730 20020 18770

0.32 0.42 0.62

20855 20240 19100

0.26 0.37 0.53

Figure 5. Bond lengths (given in Å) in the proton transfer system, N···H···O, calculated for the enol and keto forms of HAP and 10-HBQ. The bond lengths, which are identical in the S0 and S1 states to an error margin ±0.01 Å, are given only one time.

HAP can be observed in Figure 6. For both tautomers we can observe vibrational frequencies typical of perylene and its

of HAP. Calculations yielded a slightly lower absorption energy for the keto form (21 800 cm−1 in n-nonane) compared to that of the enol (22 345 cm−1), whereas for emission the keto form has a higher calculated transition energy (20 240 cm−1) than the enol (20 020 cm−1). Therefore, the identification of the two HAP tautomers with the aid of calculations is a difficult task. The calculated bond lengths of the optimized enol and keto forms of HAP are given in Table 2S. The effect of the OH substitution concerns primarily the ring adjacent to this substituent, while the remaining part of HAP is hardly affected (as compared with AP, see Figure 1S). In Figure 5 we list bond lengths (d) characterizing the N···H···O system in the enol and keto forms of HAP, compared to a typical ESIPT molecule such as 10-HBQ (i.e., in the ground state the only stable form is enol, whereas in the S1 state the molecule relaxes without barrier to the keto form). The most important observation is that the distance between the N and O atoms is considerably shorter (2.54 Å) in HAP than it is in 10-HBQ (2.60 Å). This is (partly) due to the increased rigidity of the HAP molecule. Furthermore, the hydrogen bonding lengths in the enol (N···H) and keto (O···H) forms of 10-HBQ (both equal to 1.69 Å) are longer (by 0.06−0.1 Å) compared to the corresponding bond lengths in HAP. The shorter distances have to be connected with stronger interactions in HAP than in 10-HBQ,and it seems to be the most probable reason for barriers for the proton transfer between the enol and keto forms of the HAP molecule. From a spectroscopic point of view, substitution of the OH group leads to a larger distortion of symmetry compared to perylene and AP. More vibrations have a nonzero displacement parameter, and thus a larger number of vibrational modes contribute to the electronic transition. The complexity of the calculated fluorescence spectra of the enol and keto forms of

Figure 6. Calculated Franck−Condon factors for the vibrational S1 → S0 (fluorescence) transitions in the enol and keto forms of HAP.

relatives, such as those at ∼350 and ∼550 cm−1. The spectra of both forms differ the most between 1200 and 1600 cm−1. In the case of the enol form there are several lines, among them three with relatively big and comparable intensity. This type of intensity distribution (with overlapping lines) may lead to observation of a broad band, such as that observed for the isomer B around 17 900 cm−1 (see Figure 4b). In the case of the keto form, there is a single, intense line at ∼1550 cm−1. Such a spectrum is reminiscent of the fluorescence spectrum of isomer A (see Figure 4a). Thus, we propose that the experimentally distinguished isomer A be assigned to the keto 2113



Article

tautomers of HAP have stable local potential energy minima separated by low energy barriers not only in the electronic lowest excited state, S1, but also in the ground state, S0. HAP is reminiscent of the system with nearly symmetric, doubleenergy-minimum potential for the enol−keto tautomerization in both electronic states. Each form has its own absorption and fluorescence spectra. However, a bathochromic shift of fluorescence attributed to the keto form (which typically is regarded as an indicator of an uprising of this form) is not observed. Thus, HAP can be considered as the limiting case of the ESIPT system, constituting the first example of an aromatic compound possessing an N···H−O hydrogen bond with two stable tautomeric forms, in the ground and excited electronic states. Stabilization of the keto form in polar solvents and the enol form in nonpolar solvents is correlated with a significant difference in fluorescence quantum yield in solution.16 Our detailed study has led to the following notable findings: (1) Experimental evidence shows the existence of two isomers of HAP, and theoretical calculations support their identification as the enol and keto forms. The energy and vibrational structure of the spectra suggest that the experimentally distinguished isomer A, which has the (0, 0) transition energy at 18 980 ± 10 cm−1 in the low energy site (and 19 060 ± 10 cm−1 in the high energy site), should be identified with the keto form of HAP, whereas the isomer B, with the (0, 0) transition energy at 19 200 ± 20 cm−1 in the low energy site (and 19 290 ± 20 cm−1 in the high energy site), with the enol form. (2) The unexpectedly weak stabilization of the keto form of HAP in the excited S1 state (and weak stabilization of the enol form in the S0 state) is most probably connected with the rigidity of the perylene skeleton. The geometrical constraints force the N and O atoms closer than in more flexible 10-HBQ (which is an ESIPT chromophore). (3) The fluorescence spectrum of AP in an n-heptane matrix at 5 K (treated as a link between the well-known compound perylene and HAP) was in good agreement with the calculated vibrational modes. Finally, we would like to mention that the presented work leaves many interesting questions unanswered and thus opens the door for further investigation. The lack of a (0, 0) line in the fluorescence spectrum of isomer A (Figure 4a) is intriguing. Furthermore, one should expect that if a sufficiently high excitation energy is used, so that the energy barrier in the S1 state is overcrossed, the relative intensity of fluorescence attributed to isomers A and B, which corresponds to relative population of the keto and enol forms of HAP, should reach a constant value. However, our experiment showed that this ratio is wavelength dependent within the broad absorption range presented in Figure 3. This observation is in line with the conclusion that the dynamics of the proton transfer reaction in the S1 state depend strongly on the complex multidimensional potentials involved in the process.24−26 A very strong evidence for the coexistence of the enol and keto forms of HAP in the electronic ground state would be provided to identify the O·H and NH stretching vibrations in the infrared spectrum of this compound. Such the identification is usually a difficult task27 because the energy barrier separating both forms is smaller than the frequencies attributed to

form of HAP, and isomer B to the enol form. This assignment was used in the description of vibrational structure of the spectra provided in the last columns of Tables 4 and 5. Table 4. Vibrational Progression of Lines Observed in the Fluorescence, Fluorescence Excitation, and Absorption Spectra Which Were Attributed to Isomer A (in Its High Energy Site)a experiment νi 19060 18840 18610 18520 18315 18100 17890 17565 17470 17230 17030 19060 19115 19215 19430

Δν = ν(0, 0) − νi

calculations

Fluorescence 0 (0, 0) 220 245 450 440 540 549 and/or 569 745 748 and/or 783 960 957 1170 1170 1495 1491 and/or 1503 1590 1531 1830 245 + 1531 2030 440 + 1531 Fluorescence Excitation and/or Absorption 0 (0, 0) 55 56 155 166 370 350 and/or 406

Calculated vibrational frequencies (in cm−1) are given for the keto form of HAP.

a

Table 5. Vibrational Progression of Lines Observed in the Fluorescence, Fluorescence Excitation, and Absorption Spectra Which Were Attributed to Isomer B (in Its Low Energy Site)a experiment νi

Δν = ν(0, 0) − νi

calculations

Fluorescence 19200 0 (0, 0) 17896 1304 1250, 1318, 1335, 1387 Fluorescence Excitation (flexc) and Absorption (abs) 19200 (flexc) 0 (0, 0) 19660 (abs) 460 441 19670 (flexc) 470 ∼20500 (abs) 1300 1261, 1318, 1356, 1390 ∼21000 (abs) 1800 441 + 1318, 441 + 1356, 441 + 1390 ∼21750 (abs) 2550 2 × 1318, 2831 ∼23000 (abs) 3900 3 × 1318

Calculated vibrational frequencies (in cm−1) are given for the enol form of HAP.

a

The results of our calculations and interpretation of the spectra of HAP are not as explicit as in the case of AP. It seems that our calculations do not correctly estimate the displacement parameters for the out-of-plane vibrational modes which contribute to the experimentally observed absorption (and fluorescence excitation) spectrum of isomer A. A larger, out-of plane deformation of the HAP molecule, which was not taken into account by our calculations, results in a lower intensity of the (0, 0) line with respect to the vibronic components.

IV. CONCLUSIONS AND SUMMARY The most important finding resulting from both photophysical measurements and calculations is that the enol and keto 2114



Article

2 1994, 1603−1994. (f) Bulska, H.; Grabowska, A.; Grabowski, Z. R. J. Lumin. 1986, 35, 189−197. (5) (a) Jung, H. S.; Kim, H. J.; Vicens, J.; Kim, J. S. Tetrahedron Lett. 2009, 50, 983. (b) Van Benthem, M. H.; Gillispie, G. D. J. Phys. Chem. 1984, 88, 2954. (c) Smith, T. P.; Zaklika, K. A.; Thakur, K.; Barbara, P. F. J. Am. Chem. Soc. 1991, 113, 4035. (d) Schmidtke, S. J.; Underwood, D. F.; Blank, D. A. J. Am. Chem. Soc. 2004, 126, 8620. (6) (a) Rode, M. F.; Sobolewski, A. L. J. Phys. Chem. A 2010, 114, 11879. (b) Sobolewski, A. L.; Domcke, W.; Hättig, C. J. Phys. Chem. A 2006, 110, 6301−6306. (c) Nowak, M. J.; Nowacki, J.; Rode, M. F.; Sobolewski, A. L. ChemPhysChem 2009, 10, 2290−2295. (7) (a) Kim, J. S.; Quang, D. T. Chem. Rev. 2007, 107, 3780. (b) In Chemosensors: Principles, Strategies, and Applications; Wang, B., Anslyn, E. V., Eds.; Wiley: New York, 2011; pp 253−273. (8) (a) Chou, P. T.; McMorrow, D.; Aartsma, T. J.; Kasha, M. J. Phys. Chem. 1984, 88, 4596. (b) Acuna, A. V.; Amat-Guerri, F.; Catalán, J.; Costella, A.; Figuera, J.; Munoz. J. Chem. Phys. Lett. 1986, 132, 576. (c) Sakai, K. I.; Tsuzuki, T.; Itoh, Y.; Ichikawa, M.; Taniguchi, Y. Appl. Phys. Lett. 2005, 86, 081103. (9) (a) Kim, S.; Park, S. Y. Adv. Mater. 2003, 15, 1341. (b) Kim, S.; Park, S. Y.; Tashida, I.; Kawai, H.; Nagamura, T. J. Phys. Chem. B 2002, 106, 9291. (10) Catalán, J.; del Valle, J. C.; Claramunt, R. M.; Sanz, D.; Dotor, J. J. Lumin. 1996, 68, 165. (11) (a) Roshal, A. D.; Grigorovich, A. V.; Doroshenko, A. O.; Pivovarenko, V. G. J. Phys. Chem. A 1998, 102, 5907. (b) Landge, S. M.; Tkatchouk, K.; Benitez, D.; Lanfranchi, D. A.; Elhabiri, M.; Goddard, W. A. III; Aprahamian, I. J. Am. Chem. Soc. 2011, 133, 9812. (12) Parsapour, F.; Kelley, D. F. J. Phys. Chem. 1996, 100, 2791. (13) Sytnik, A.; Kasha, M. Proc. Natl. Acad. Sci. U.S.A. 1994, 91, 8627. (14) (a) Kim, S.; Seo, J.; Jung, H. K.; Kim, J. J.; Park, S. Y. Adv. Mater. 2005, 17, 2077. (b) Park, S.; Kwon, J. E.; Kim, S. H.; Seo, J.; Chung, K.; Park, S.-Y.; Jang, D.-J.; Medina, B. M.; Gierschner, J.; Park, S.-Y. J. Am. Chem. Soc. 2009, 131, 14043. (15) (a) Martinez, M. L.; Cooper, W. C.; Chou, P. T. Chem. Phys. Lett. 1992, 193, 151. (b) Chou, P. T.; Wei, C. Y. J. Phys. Chem. 1996, 100, 17059. (c) Takeuchi, S.; Tahara, T. J. Phys. Chem. A 2005, 109, 10199−10207. (d) Paul, B. K.; Guchhait, N. J. Lumin. 2011, 131, 1918−1926. (e) Higashi, M.; Saito, S. J. Phys. Chem. Lett. 2011, 2, 2366−2371. (f) Piechowska, J.; Gryko, D. T. J. Org. Chem. 2011, 76, 10220. (16) Gryko, D. T.; Piechowska, J.; Gałez̨ owski, M. J. Org. Chem. 2010, 75, 1297−1300. (17) (a) Lambert, W. R.; Felker, P. M.; Syage, J. A.; Zewail, A. H. J. Chem. Phys. 1984, 81, 2195. (b) Baranov, V. I. J. Appl. Spectrosc. 2000, 67, 198. (c) Klaumünzer, B.; Kröner, D.; Saalfrank, P. J. Phys. Chem. B 2010, 114, 10826−10834. (d) Dierksen, M.; Grimme, S. J. Chem. Phys. 2004, 120, 3544. (18) Gooijer, C.; Ariese, F.; Hofstraat, J. W. Shpol’skii Spectroscopy and Other Site-Selection Methods; Wiley & Sons: New York, 2000. (19) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery , J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Keith, T.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09, revision B.01; Gaussian Inc.: Wallingford, CT, 2010. (20) Berces, A.; Zgierski, M. Z.; Yang, D.-S. In Computational Molecular Spectroscopy; Jensen, P., Bunker, P., Eds.; John Wiley: Chichester, U.K., 2000; p 119.

mentioned vibrations. Thus, it will be the subject of forthcoming investigation. These results are not only of theoretical significance in the sense that they provide new insight into factors influencing the occurrence of excited-state intramolecular proton transfer, but they may also open the door to practical applications: 1-hydroxy-1-azaperylene serves as the first example of new class of molecules which can be suitable for fluorescent platforms.

■

ASSOCIATED CONTENT

S Supporting Information *

Optimized structure and coordinate displacement vectors of AP; frequencies, reduced masses, and IR intensities of vibrational modes of AP and HAP; bond lengths and transition energies of HAP. This material is available free of charge via the Internet at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Author

*Phone (+48-22) 843 66 01-3285; fax (+48-22) 843 09 26; e-mail [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS Theoretical calculations were performed at the Interdisciplinary Center of Mathematical and Computer Modeling (ICM) of the Warsaw University under the computational grant no. G-32-10. This work was also supported by the European Regional Development Fund TEAM Program (Foundation for Polish Science, TEAM-2009-4/3). We thank Eva Nichols (Caltech) for amending the manuscript.

■

REFERENCES

(1) (a) Kwon, J. E.; Park, S. Y. Adv. Mater. 2011, 23, 3615−3642. (b) Fang, C.; Frontiera, N. N.; Tran, R.; Mathies, R. A. Nature 2009, 462, 200−204. (c) Iijima, T.; Momotake, A.; Shinohara, Y.; Sato, T.; Nishimura, Y.; Arai, T. J. Phys. Chem. A 2010, 114, 1603−1609. (d) Shono, H.; Ohkawa, T.; Tomoda, H.; Mutai, T.; Araki, K. ACS Appl. Mater. Interfaces 2011, 3, 654−657. (e) Chen, K.-Y.; Cheng, Y.-M.; Lai, C.-H.; Hsu, C.-C.; Ho, M.-L.; Lee, G.-H.; Chou, P.-T. J. Am. Chem. Soc. 2007, 129, 4534−4535. (2) (a) Mordziński, A.; Grabowska, A.; Kuhnle, W.; Krowczyński, A. Chem. Phys. Lett. 1983, 101, 291. (b) Frey, W.; Laermer, F.; Elsaesser, T. J. Phys. Chem. 1991, 95, 10391. (c) Das, K.; Sarkar, N.; Majumda, D.; Bhattacharyya, K. Chem. Phys. Lett. 1992, 198, 443. (d) Fores, M.; Duran, M.; Sola, M.; Adamowicz, L. J. Phys. Chem. A 1999, 103, 4413. (e) Wang, H.; Zhang, H.; Abou-Zied, O. K.; Yu, C.; Romesberg, F. E.; Glasbeek, M. Chem. Phys. Lett. 2003, 367, 599. (f) Rini, M.; Dreyer, J.; Nibbering, E. T. J.; Elsaesser, T. Chem. Phys. Lett. 2003, 374, 13. (3) (a) McMorrow, D.; Kasha, M. J. Phys. Chem. 1984, 88, 2235. (b) Strandjord, A. J. G.; Smith, D. E.; Barbara, P. F. J. Phys. Chem. 1985, 89, 2362. (c) Chou, P.-T.; Chen, Y.-C.; Yu, W.-S.; Chen, Y.-M. Chem. Phys. Lett. 2001, 340, 89. (d) Svechkarev, D. A.; Karpushina, G. V.; Lukatskaya, L. L.; Doroshenko, A. O. Cent. Eur. J. Chem. 2008, 6, 443−449. (e) Svechkarev, D. A.; Dereka, B. A.; Doroshenko, A. O. J. Phys. Chem. A 2011, 115, 4223−4230. (4) (a) Druzhinin, S. I.; Rodchenkov, G. M.; Uzhinov, B. M. Chem. Phys. 1988, 128, 383. (b) LeGourrierec, D.; Kharlanov, V. A.; Brown, R. G.; Rettig, W. J. Photochem. Photobiol., A 2000, 130, 101. (c) Chen, K.-Y.; Cheng, Y.-M.; Lai, C.-H.; Hsu, C.-C.; Ho, M.-L.; Lee, G.-H.; Chou, P.-T. J. Am. Chem. Soc. 2007, 129, 4534−4535. (d) Kanda, T.; Momotake, A.; Shinohara, Y.; Sato, T.; Nishimura, Y.; Arai, T. Bull. Chem. Soc. Jpn. 2009, 82, 118−120. (e) Kaczmarek, Ł.; Balicki, R.; Lipkowski, J.; Borowicz, P.; Grabowska, A. J. Chem. Soc., Perkin Trans. 2115



Article

(21) Joblin, C.; Salama, F.; Allamandola, L. J. Chem. Phys. 1999, 110, 7287−7297. (22) Walla, P. J.; Jelezko, F.; Tamarat, Ph.; Lounis, B.; Orrit, M. Chem. Phys. 1998, 233, 117−125. (23) Pirotta, M.; Renn, A.; Werts, M. H. V.; Wild, U. P. Chem. Phys. Lett. 1996, 250, 576−582. (24) McCarthy, A.; Ruth, A. A. Phys. Chem. Chem. Phys. 2011, 13, 7485−7499. (25) Chen, K. Y.; Hsien, C. C.; Cheng, Y. M.; Lai, C. H.; Chou, P. T. Chem. Commun. 2006, 4395−4397. (26) Schriever, C.; Barbatti, M.; Stock, K.; Aquino, A. J. A.; Tunega, D.; Lochbrunner, S.; Riedle, E.; de Vivie-Riedle, R.; Lischka, H. Chem. Phys. 2008, 347, 446−461. (27) Mordziński, A.; Nowak, M. J.; Lipkowski, J. J. Mol. Struct. 1990, 219, 209−214.

2116


12-Hydroxy-1-azaperyleneâLimiting Case of the ... - ACS Publications

Recommend Documents

12-Hydroxy-1-azaperyleneâLimiting Case of the ... - ACS Publications