J . Phys. Chem. 1989, 93, 1826-1832 (1394 and 1404 cm-]) for the identical H-N-0 angle bends, because the use of one H-N-0-H torsion does not treat the two bends equivalently. Replacement of the H-N-H bend with the second symmetry-equivalent H-N-0-H torsion (set B) yields equal intrinsic frequencies for the two H-N-0 bends. However, the intrinsic frequency for the torsions is unusually large (1 17 1 cm-') compared to the corresponding normal-coordinate torsion frequency of 450 cm-' (not given in Table XI). Set B thus illustrates the result of not choosing the minimal number of torsions in obtaining a vibrationally complete set of internal coordinates. Set C accounts for the symmetry of the H-N-O bends and yields a physically reasonable intrinsic frequency for the torsion (457 cm-') as well. To further illustrate the importance of symmetry, consider the CZh(anti) conformer of hydrazine, N2H4,shown in Chart 111. (X and Y are points midway between the hydrogens at each end of the molecule.) In the above chart all four H atoms are symmetrically equivalent. Consider three sets of internal coordinates that are complete, satisfy the symmetry requirements for angle bends, and use the minimal number of coordinates (12). These three sets, denoted as D, E, and F, have the five stretches, the four H-N-N angle bends, and the two H-N-H bends in common. Sets D, E, and F include the Ha-N-N-H,, H,-N-N-Hd, and X-N-N-Y torsions, respectively. The intrinsic frequencies obtained by using these three sets are given in Table XII. For set F, symmetry-equivalent internal coordinates have equal intrinsic frequencies, but the same is not true for sets D and E. That set
F properly accounts for the symmetry of hydrazine is a direct result of the symmetrical nature of the X-N-N-Y torsion. Sets D and E, on the other hand, include the Ha-N-N-H, and Ha-N-N-Hd torsions, respectively, which do not treat all four symmetrically equivalent hydrogen atoms equally. In the case of the C2 (gauche) conformer of hydrazine, all four hydrogen atoms are no longer equivalent to each other. Rather, only the Ha-Hd and Hb-H, pairs are equivalent (see Chart IV). Since the Ha-Hb and H,-Hd pairs are not symmetrically equivalent, the choice of an appropriate torsion angle is more flexible. That is, the Ha-N-N-Hd, Hb-N-N-H,, and X-N-N-Y torsions (sets G, H, and I, respectively, in Table XII) all properly account for the symmetry of the gauche conformer of hydrazine. However, the Ha-N-N-H, torsion (set J in Table XII) fails in this regard since Ha and H, are not equivalent. The above observations suggest the following guidelines for using torsion angles in computing intrinsic frequencies: (1) The minimum number of torsions sufficient to attain completeness should be used. (2) The torsion angles used must treat symmetrically equivalent atoms in an equivalent manner. Registry No. H20, 7732-18-5; NH,, 7664-41-7; CH,, 74-82-8; CHECH, 74-86-2;CH,=CH2, 74-85-1; CH,-CH3,74-84-0; CHI-CH2-CH2, 75-19-4; CH,-(CH2)2-CH2, 287-23-0; CH2-(CH2),-CH2, 287-92-3; CH2-(CHI),-CHI, 110-82-7;benzene, 71-43-2;bicyclobutane,
-
I
157-33-5.
Phosphorescence of trans-Stllbene, Stilbene Derivatives, and Stilbene-like Molecules at 77 K Helmut Gorner Max-Planck- Institut fur Strahlenchemie, 0-4330 Miilheim an der Ruhr, West Germany (Received: July 8, 1988)
For some rigid stilbene analogues and various trans- 1,2-diarylethyIenes, including styrylpyridines, dipyridylethylenes, and a series of substituted stilbenes, phosphorescence spectra and lifetimes ( T ~ were ) determined in nonpolar and polar glasses at 77 K, partly in the presence of 2-10% ethyl iodide. The triplet energies range from 52.2 kcal/mol for indenot2,l-aIindene to 45.2 kcal/mol for trans-4-nitro-4'-methoxystilbene. The T~ values are in the IO-ms domain, and they are shorter when the internal or external heavy-atom effects are involved. The quantum yield of phosphorescence (a,) of trans-4-nitrostilbene and the parent stilbene is 3 X and 51 X respectively. The aPvalues reflect the changes in the quantum yield of intersystem crossing (ais)and the ratio of the rate constants for the radiative (k,) and nonradiative (k",) triplet decay , and ais,values transitions. These values are of the order of k, = 0.05 s-' and k,, = 100 s-l, as concluded from the T ~ aP, of 4-aceto-, 4-benzoyl-, and 4-nitrostilbene in several glassy media.
Introduction Generally, information about the triplet state of aromatic molecules is easily obtained from the phosphorescence spectra in glassy media.' However, phosphorescence is difficult to observe with compounds containing a styrene or stilbene chromophore.24 To the best of our knowledge, only a few studies have been published on the phosphorescence of trans-stilbene and stilbene-like compound^.^-^ Not even for tran~-4-nitrostilbenes,6-~ where the (1) Birks, J. B. Photophysics of Aromaric Molecules; Wiley-Interscience: London, 1970. (2) Lamola, A. A.; Hammond, G. S . ; Mallory, F. B. Phorochem. Phorobiol. 1965, 4 , 259. (3) Saltiel, J.; Khalil, G.-E.; Schanze, K. Chem. Phys. Lett. 1980, 70, 233; Ibid. 1980, 73, 199. (4) (a) Piister, D. Diplomarbeit, Universitat Gottingen, 1983. (b) Liitke, W. Private communication. ( 5 ) Ikeyama, T.; Azumi, T. J . Phys. Chem. 1985,89, 5332; Ibid. 1988,92, 1383. (6) Bent, D. V.;Schulte-Frohlinde, D. J . Phys. Chem. 1974, 78, 446 and 451.
quantum yield of fluorescence (af)is generally small while that equals up to 0.9), has for intersystem crossing is substantial (+is phosphorescence data been reported so far. Saltiel et al. have reported phosphorescence maxima (Amax) of 580 and 601 nm for trans-stilbene and the rigid analogue indeno[2,1-~]indene,re~pectively.~ The former value is confirmed here, whereas the latter is slightly revised. The energy of the triplet state ( E T ) of stilbene has been determined by other methods, such as UV/vis absorption under high pressure of oxygen9 or in a heavy-atom solventi0 and by energy(7) Schulte-Frohlinde, D.; Garner, H. Pure Appl. Chem. 1979, 51, 279. (8) (a) Gorner, H. Ber. Bunsen-Ges. Phys. Chem. 1984, 88, 1199. (b) Garner, H.; Schulte-Frohlinde, D. Ber. Bunsen-Ges. Phys. Chem. 1984,88, 1208. (9) (a) Evans, D. F. J . Chem. Soc. 1957, 1351. (b) Bylina, A.; Grabowski, Z . R. Trans. Faraday Soc. 1969,65,458. (c) Alder, L.; Gloyna, D.; Wegener, W.; Pragst, F.; Henning, H.-G. Chem. Phys. Lett. 1979, 64, 503. (d) Malan, 0. G.; Giisten, H.; Schulte-Frohlinde, D. J . Phys. Chem. 1968, 72, 1457. (10) (a) Dyck, R. H.; McClure, D. S . J . Chem. Phys. 1962,36, 2326. (b) Stegemeyer, H. Z . Phys. Chem. (Munich) 1966, 51, 95.
0022-3654/89/2093-1826$01.50/00 1989 American Chemical Society
Phosphorescence of Stilbenes and Stilbene Analogues transfer measurements." The ET values, commonly used for trans- and cis-stilbene, are 49 and 57 kcal/mol, respectively.12 For the relaxed triplet of the two stilbene isomers ET = 44 kcal/mol has been measured by photoacoustic calorimetry in acetonitrile at 300 K.13, Values of 46.5 and 42.0 kcal/mol for trans- and cis-stilbene in cyclohexane, respectively, have recently been obtained by Caldwell and his group using an improved technique.13bThe triplet lifetime of stilbene-like molecules has been determined by T-T absorption (7m)6,7,14-28rather than by emission spectroscopy. The triplet lifetime (5-22 ms) of transstilbene in rigid media at 77 K has also been determined in an ESR study.29 For molecules that can twist about their C=C bond, the phosphorescence quantum yield (aP)is apparently strongly reduced. There is therefore a lack of phosphorescence data for 1,2-diarylethylenes. This paper presents improved phosphorescence measurements of trans-stilbene and its analogues at 77 K as well as new spectral and kinetic phosphorescence results for a series of stilbenes and related trans-1 ,2-diarylethylenes.
Experimental Section The emission spectra were recorded either on a Spex-Fluorolog (corrected) or on a Perkin-Elmer LS-5 (noncorrected). The former spectrofluorometer is more sensitive in the red spectral range (photomultiplier, RCA C31034; bandwidth, 2.5-10 nm). Therefore, a third phosphorescence peak, in addition to the two observed with the latter instrument, could be recorded in most cases. In order to reveal the phosphorescence better, an appropriate cutoff filter was used in all cases. The LS-5 (photomultiplier, EM1 978 1RA; bandwidth, 5-10 nm) enables considerable enhancement of the intensity ratio of phosphorescence vs fluorescence (Zp/If) and allows the measurement of T~ by application of a time gate in the 0.01-10-ms range. The T, values (experimental error *30%) were obtained at A, (major peak) under the same conditions as for the spectra. Measurements of T~ with our laser setup failed due to extremely strong fluorescence and/or scattering of light even around 600 nm. Some triplet lifetimes were also determined by T-T absorption using laser flash photolysis (argon-saturated solutions, A, = 353 nm, and 248 nm for samples not absorbing at 353 nm) as described elsewhere.1e25 The solutions were studied at 77 K in quartz cuvettes (cylindrical, diameter about 5 mm or rectangular), without degassing unless otherwise indicated. The study of ketostilbenes30 and
(1 1) Herkstroeter, W. G.; Hammond, G. S. J . Am. Chem. SOC. 1966,88, 4769. (12) Saltiel, J.; Charlton, J. L. In Rearrangements in Ground and Excited States; de Mayo, P., Ed.; Academic Press: New York, 1980; Vol. 3, p 25. (13) (a) Lavilla, J. A.; Goodman, J. L. Chem. Phys. Lett. 1987, 141, 149. (b) Tuqiang, Ni.; Caldwell, R. A.; Melton, L. A. Submitted for publication. (14) Heinrich, G.; Blume, H.; Schulte-Frohlinde, D. Tetrahedron Lett. 1967, 4693. (15) Herkstroeter, W. G.; McClure, D. S . J . Am. Chem. SOC.1968, 90, 4522. (16) Heinrich, G.; Holzer, G.; Blume, H.; Schulte-Frohlinde, D. Z.Naturforsch., B: Anorg. Chem., Org. Chem. 1970, 25, 496. (17) Heinrich, G.; Giisten, H.; Mark, F.; Olbrich, G.; Schulte-Frohlinde, D. Ber. Bunsen-Ges. Phys. Chem. 1973, 77, 103. (18) Saltiel, J.; D'Agostino, J. T.; Herkstroeter, W. G.; Saint-Ruf, G.; Buu-Hoi, N. P. J . Am. Chem. SOC.1973, 95, 2543. (19) Garner, H.; Schulte-Frohlinde, D. J . Phys. Chem. 1979, 83, 3107. (20) Gorner, H.; Schulte-Frohlinde, D. J . Phys. Chem. 1985, 89, 4105. (21) Gorner, H.; Fojtik, A.; Wrbblewski, J.; Currell, L. J. Z.Nuturforsch., A: Phys., Phys. Chem., Kosmophys. 1985, 40, 525. (22) Gorner, H.; Schulte-Frohlinde, D. Chem. Phys. Lett. 1983, 101, 79. (23) Gorner, H. J . Photochem. 1980, 13, 269. (24) Gorner, H.; Schulte-Frohlinde, D. J . Phys. Chem. 1981, 85, 1835. (25) Gorner, H. J . Phys. Chem. 1982,86, 2028. (26) Elisei, F.; Mazzucato, U.; Gorner, H.; Schulte-Frohlinde, D. J . Photochem. 1987, 37, 87. (27) Gorner, H.; Elisei, F.; Mazzucato, U.; Galiazzo, G . J . Photochem. Phorobiol. 1988, 43A, 139. (28) Gorner, H.; Schulte-Frohlinde, D. Work in preparation. (29) Yagi, M. Chem. Phys. Lett. 1986, 124, 459. (30) Gegiou, D.; Muszkat, K. A.; Fischer, E. J . Am. Chem. SOC.1968,90, 3907.
-
The Journal of Physical Chemistry, Vol. 93, No. 5, 1989 1827 h(nm) 500
400
600
700
1
I
0.5
0 26
-
24
22
20 18 v(cm.'.1o3)
16
14
Figure 1. Corrected emission spectrum a t 77 K (a) of trans-4-benzoylstilbene in ethanol, (b) and (c) of trans-4-benzoylstilbene and trans-4acetostilbene in butyronitrile, respectively; A,, = 340 nm.
nitrostilbenes in nonpolar solvents is complicated by precipitation dllU d ~ ~ l C & l l l U l l .
1 IICSC ~ I I C I I U I I I C I I dL d l I UC d V U I U C U , dl I C d > l 111
part, by rapid cooling, as was done for the emission studies throughout. The quantum yields afand 9,were measured on the Spex-Fluorolog in dilute, argon-saturated solutions (in the absence of a heavy-atom solvent) with an absorbance ( A ) of only about 0.2 at A,., In contrast, for most other phosphorescence measurements in this work much larger concentrations were used. Ofand Q, values were determined from the integrated corrected spectra, using af= 0.90 for trans-stilbene in ethanol19as reference. The compounds are trans isomers throughout and are the same as those previously used except where i n d i ~ a t e d . ~ * -In ' ~the J~~~ case of 4,4'-dinitrostilbene a trace impurity gave rise to phosphorescence in the 500-nm range which, however, did not influence the phosphorescence spectrum and lifetime at 620-700 nm. 4Iodo- and 4-benzoylstilbene were prepared by conventional method^.^^^' Identical spectra were recorded for two different indeno[ 2,1-a] indene samples, kindly provided by Dr. H. Giisten and Prof. W. Luttke, and two 2-phenylindene samples, one from the latter colleague and one as used p r e v i ~ u s l y . ~trans-4~ AcetostilbenejO was donated by Prof. E. Fischer and trans-3,3'dibromostilbene by Prof. J. Saltiel. The colvents (Merck or Fluka) were distilled: 2-methyltetrahydrofuran (MTHF), butyronitrile, ethyl iodide (EtI), and m-dibromobenzene; or used as received: glycerol triacetate (GT), ethanol, z.A., 2,2-dimethylbutane/npentane, (D-P, Uvasol, 8:3 mixture). Recording of the phosphorescence spectra is made difficult by the following factors: (1) The aPvalue of many trans- 1,2-diarylethyIenes is extremely small. This restricts phosphorescence measurements without time value of 77 K. delay to those compounds having a very small aPr (2) For a sample with a afvalue close to unity the fluorescence If value at around 600 nm is still too high. (3) Addition of Et1 leads to a red-shift of the absorptionloband reduces the fluorescence and/or increases the triplet population; cf. ref 1 and 3. However, it also enhances the second intersystem-crossing transition (%* It), thereby decreasing T~ and aP. (4) The high stilbene concentrations, necessary to induce fluorescence self-quenching, and the absorption of EtI, when added, restrict the excitation range to X 2 320 nm. Unfortunately, no excitation spectra could be recorded under conditions 3 and 4. The optimum conditions for recording phosphorescence spectra of compounds with large af(and absorption maximum below 320 nm) were obtained by applying (i) the longest possible A,, e.g.,
-
(31) Herbert, H.-J. Studienarbeit Fachhochschule Niederrhein, Krefeld (carried out in the MPI Miilheim), 1977.
1828
The Journal of Physical Chemistry, Vol. 93, No. 5, 1989
Gorner
TABLE I: Triplet Energy and Phosphorescence Maxima and Lifetime of 4-Substituted trnns-Stilbenes in Glassy Media at 77 K" compound 4-acetostilbene
4-benzoylstilbene
4-iodostilbene
4-nitrostilbene
solvent D-F MTHFc GT' butyronitrile ethanol MTHF GT butyronitrile ethanol D-P GT butyronitrile ethanol MTHF GT butyronitrile ethanol
ET, kcal/mol 47.7 47.4 47.3 47.3 47.3 47.3 41.2 47.3 47.3 47.8 47.8 47.8 47.8 46.5 46.4 46.6 46.6
A,, nm 600, 666 603, 667, 735 604, 665, 734 604, 664, 734 604, 666, 736 605, 665, 735 606, 661, 736 605, 666, 730 604, 665, 736 598, 648 598, 650, 733 598, 650, 732 598, 650, 732 615, 670, 746 616, 670, 745 614, 673, 744 614, 673, 745
T
~
ms,
h(r"
LOO
500
600
700
~
9 8 9 8 (8)d 9 (9)d 8 11
IO 0.1 0.1 0.08 (0.1) 0.08 9 I O (10)' IO I O (11)
In air-saturated solution in the absence of a heavy-atom solvent, A, = 350-380 nm, corresponding to A = 0.1-1. bValues in parentheses refer to T-T absorption. e 2,2-Dimethylbutane/n-pentane(D-P, 8:3); 2-methyltetrahydrofuran (MTHF); glycerol triacetate (GT). dTaken from ref 28. CTakenfrom ref 7.
0 1 26
-
1
1
24
1
22
18
16
14
g(c:2x103)
Figure 2. Corrected emission spectrum in butyronitrile a t 77 K (a) of trans-4-nitrostilbene, (b) of trans-1-methyl-4- [4-nitrostyryl]pyridinium iodide, A,, = 340 nm, and (c) of trans-4,4'-dipyridylethylene, A, = 320 nm.
2335 nm; (ii) a high concentration, corresponding to A(&,,) < 0.01A3,, in most cases; (iii) 2-10% (vol) EtI; and (iv) an ap-
1
propriate time delay, e.g., 0.1-1 ms.
Results The emission spectrum of trans-4-benzoylstilbene in ethanol at 77 K reveals two major maxima at 400 and 420 nm and three minor maxima at 604, 665, and 736 nm (Figure la). There is no doubt that the higher and lower energy bands are to be attributed to fluorescence and phosphorescence, respectively. Very similar spectra were recorded for this compound and for trans4-acetostilbene in butyronitrile (Figure lb,c), as well as for trans-4-nitrostilbene (Figures 2a and 3b) and trans- 1methyl4- [4-nitrostyryl]pyridinium iodide (quaternary stilbazolium salt) in polar solvents (Figure 2b). The excitation spectra of both the phosphorescence and the fluorescence bands are practically the same, which indicates that the samples are pure and that the excited trans singlet state is the origin of both processes. Spectroscopic data of some 4-substituted trans-stilbenes that exhibit phosphorescence in the absence of a heavy-atom solvent were obtained in 2,2-dimethylbutane/n-pentane (D-P), 2methyltetrahydrofuran (MTHF), butyronitrile, and ethanol as examples of nonpolar, moderately polar, and highly polar solvents, and of alcohols, respectively (Table I). Glycerol triacetate (GT), although not transparent at 77 K, also turned out to be a suitable solvent, and was used since triplet lifetimes of a number of stilbenes in glassy GT at 11200 K have already been reported.'^'^ As to the rigid trans-stilbene analogues (Scheme I) and most of the stilbenes, phosphorescence at 77 K could only be detected
1:
05
0'
,
-
18
1
I
14
1
v(cmltri03)
Figure 3. Corrected phosphorescence spectrum in ethanol at 77 K of (a) indeno[2,1-a]indene in the presence of 10% Et1 and (b) trans-4-nitrostilbene, A,, = 335 nm.
in the presence of a heavy-atom solvent (Table I1 and 111). Suppression of the fluorescence band, extending into the red spectral range, is best achieved by (i) excitation in the longwavelength range, (ii) addition of ethyl iodide (EtI), and (iii) application of a time delay. The phosphorescence spectra of indeno[2,1 -a]indene, 2-phenylindene, trans-stilbene, trans-4iodostilbene, and trans-4-nitro-4'-methoxystilbenein glassy eth-
TABLE 11: Triolet Enerev and PhosDhorescence Maxima and Lifetime of Stilbene and Its Analogues in Classy Media at 77 K' compound solvent % Et1 ET, kcal/mol Amax, nm T , , ~ ms 0 61.4 phenanthrene ethanol 466, 500, 540 549, 597, 653 52.1 indeno[2,1 -a]indene MTHF 5c 20' 52.3 10 547, 596, 650 54 GT ethanol 52.2 10 548, 595, 652 5 4 , 15' 50.2 2-phenylindene GT 10 570, 625, 690 54 IO 50.4 ethanol 567, 620, 680 54 49.0 583, 633 54 2 trans-stilbene D-P 0 EPA (22Id 49.5 578, 635, 700 EPA' 48.9 585, 635, 697 53 MTHF 5 49.3 580, 636, 698 5 3 (IO)! GT 10 580, 635, 698 54 49.3 butyronitrile 10 3.6 (12)f 5 ethanol 583, 635, 700 53 49.0 ethanol IO a In air-saturated solution, A,, = 330-340 nm, corresponding to A = 0.2-2. bValues in parentheses refer to T-T absorption in the absence of EtI. 'm-Dibromobenzene instead of EtI. dTaken from ref 14. e I n the presence of 25% butyl iodide; taken from ref 4a. 'Taken from ref 19.
The Journal of Physical Chemistry, Vol. 93, No. 5, I989 1829
Phosphorescence of Stilbenes and Stilbene Analogues SCHEME I
1
E,
R’=H
R:
. I ‘ 1
H. F
L0
0r
CH3C0, C,H,CO.
(kcal / m o l )
CN
t
I
R : CN, NO, 520
-
600
560
Ahm)
-
640
680
Figure 4. Phosphorescence spectrum (noncorrected) a t 77 K of (a) indeno[2,1-a]indene, (b) 2-phenylindene, (c) trans-stilbene, (d) trans-4iodostilbene, and (e) trans-4-nitro-4’-methoxystilbenein ethanol in the presence of 10% EtI; A,, = 330-340 nm. TABLE III: Triplet Energy and Phosphorescence Maxima and Lifetime of Substituted trans -Stilbenes in Glassy Ethanol/EtI (9:l) at 71 K” compound
ET,
49.0
A,, nm 583, 635
49.0 48.9 48.7 48.6 48.5 48.4 48.3 48.3 48.1 47.7 47.3 47.3 47.3 47.2 46.6 46.0 45.4 45.2 45.2
584, 634 585, 645 587, 636 588, 643 590, 645 591, 645 592, 645 592, 646 594, 648 599, 650 604, 666 605, 666 604, 670 606, 650 614, 673 622, 680 630, 675 633, 690 632, 690
kcal/mol
stilbene-d12 stilbene-d12 4-fluorostilbene 3-methylstilbene 3-nitrostilbene 3-methoxystilbene 4,4’-dimethoxystilbene 4-chlorostilbene 3,3’-dibromostilbene 4-methoxystilbene 4- bromostilbene 4-iodostilbene 4-acetostilbene 4-benzoylstilbene 4-cyanostilbene 2-nitrostilbene 4-nitrostilbene 4,4-’dicyanostilbene
4-cyano-4’-methoxystilbene 4,4’-dinitrostilbene 4-nitro-4’-methoxystilbene
7,:
0
0.1
(ms)
0.2
0
ms
12 12c 13 13 54 53 12 12 0.9‘ 53 0.4 (0.5)d 0.08 (O.l)d 13 13 5 3 (15)f 53 1 3 (12)f 5 2 (12)f 9F (10) loc (1O)g
‘In air-saturated solution, A,, = 330-340 nm, except for cyano- and nitrostilbenes (350-380 nm), corresponding to A = 0.2-2. ’Values in parentheses refer to T-T absorption in the absence of EtI. c I n MTHF, m-dibromobenzene instead of EtI. dTaken from ref 19. e I n the absence of EtI. /Taken from ref 23. gTaken from ref 7.
-.
o -0.5 P
0
2
4
6
8
Time ( m s )
Figure 5. Semilogarithmic plot of the relative phosphorescence intensity a t 77 K vs time: (a) trans-4-nitrostilbene in ethanol ( O ) , (b) transstilbene in ethanol/EtI (95:5) ( O ) , (c) trans-4-iodostilbene in butyronitrile ( O ) ,and (d) trans-4,4’-dipyridylethylenein ethanol/EtI (9: 1) (A).
anol/EtI are shown in Figures 3a and 4. The first phosphorescence maximum is at 548, 567, 583, 599, and 632 nm, respectively. No phosphorescence could be detected for 1,2-diphenylcy~lobutane~~ under the same conditions. Phosphorescence data of a series of substituted stilbenes and other 1,2-diarylethylenes are listed in Tables I11 and IV, re-
TABLE IV: Triplet Energy and Phosphorescence Maxima and Lifetime of trans-1,2-Diarylethylenesin Glassy Media at 77 K“ compound 4,4’-dipyridylethylene
2,2’-dipyridylethylene 3,3’-dipyridylethylene 4-styr ylpyridine 2-styrylpyridine 3-styrylpyridine 1 -methyl-4- [4-~yanostyryl]pyridiniumiodide, cyano derivatived l-methyl-4-[4-nitrostyryl]pyridiniumiodide, nitro derivative‘
h” nm
solvent
% Et1
ET, kcal/mol
D-P MTHF GT but yronitrile ethanol ethanol ethanol ethanol
2
50.6 50.8 50.9 51.2
565, 563, 562, 558,
50.5 49.5 49.3 49.8 49.7 49.2 49.0 48.8 47.4 47.0 47.3 41.0 47.2
566, 622, 684 577, 635 580, 640 574, 628 575, 628 581, 631 583, 637 586, 640 603, 658, 720 608, 668 605, 666, 727 608, 666, 728 606, 664, 728
D-P MTHF ethanol ethanol ethanol GT ethanol GT butyronitrile ethanol
0 10 0 0 10 10 10 2 5 10 10 10 10 10 10 0 0
615 612, 666 614, 615 608, 666
+p,b
ms
51 14 53 15 -12
