J. Phys. Chem. 1981, 85, 144-146
144
probability if the spins of ground-state donor and acceptor are the same and if the excited states are the same. This is clearly the case with triplet-triplet transfer but is not the case here. Triplet-doublet transfer would require a spin flip, and thus should be forbidden. However future studies with a different triplet donor (with different lifetimes) might be interesting to illuminate this point. The presence of the magnetic dipole, as with the case of the ground-state t r i ~ l e tseems , ~ to be irrelevant as far
as energy transfer is concerned. It further indicates that the use of spin labels in any light-sensitive system that involves chromophores of appropriate characteristics may be risky unless energy transfer is considered in interpreting experimental results.
Acknowledgment. This work was supported by the Atomic Energy Commission (Department of Energy) contract No. AT-11-1627.
Fluorescence of Distyrylbenzenes Terry E. Busht and Gary W. Scott' Department of Chemistry, Universtiy of California, Rivers&, Rivers&, California 92521 (Received: August 22, 1980)
Absorption, corrected emission spectra, and fluorescence quantum yields are reported for distyrylbenzene and substituted derivatives. Observed spectral features are related to excited-state conformational changes.
Introduction 1,4-Distyrylbenzene (DSB) and derivatives such as 1,4bis(2-methylstyry1)benzene(Bis-2MSB) have been utilized for many years as highly efficient blue-emitting laser dyes.14 These and related dyes in the substituted stilbene family5" are noted for their high photochemical stability, especially in comparison with the other widely used family of blue-emitting dyes, the coumarins. Limited investigations of the fluorescent characteristics of various distyrylbenzenes have been reported the most extensive investigation being one by Heller.g In the present paper we report the determination of fluorescence quantum yield and corrected emission spectra of distyrylbenzene and three substituted derivatives. These dyes are DSB, Bis-2MSB, 1,4-bis(2-methoxyD S B : RI
R2
R I = CH3 , R2' H
B i s - 2 M O S B : Rl'OCH3 ,R2"
Q,C=C, ?
~~
~
Amax, nm
molecule
DSB
Bis-2MSB
solvent absorption fluorescencea dioxane 354 390, 411.5, 430' heptane 350 385,408,429' toluene 355 392,413,442s cyclohexane 351 386, 408.5, 4305 dioxane
heptane toluene cyclohexane
Bis-2MOSB
ethanol dioxane toluene
cyclohexane
ethanol
R2' H
Bis-2MSB R,
TABLE I : Summary of Observed Spectra ~
350.5 345 350 346 346
400, 422,448' 393,416,4425 403,425,450' 397, 419,447' 398, 419,447'
366 367 362 362
408.5,431,457' 411,434,461' 407, 427, 451' 410,427,44P
Bis-4MSB
dioxane 358 395,418,443' cyclohexane 356 39 2, 4 13, 43 5' The superscript s indicates shoulder.
Bis-4MSB: RI=H,Rz=CH3
distyrylbenzenes was previously noted by Heller.g Our current reinvestigation of this problem essentially confirms his previous work. (1) V. P. Kotaubanov, L. Ya Malkes, Yu V. Naboikin, L. A. Opurtsova, A. P. Podgornyi, F. S. Pokrovskaya, and L. V. Shubina, Zh. Prik. Spektrosc., 10,-152-(1969). (2) T. F. Deutah and M. Bass, IEEE J. Quantum Electron., QE5.260 \
(1969).
R2
styry1)benzene ( B ~ s - ~ M O S Band ) , 1,4-bis(4-methylstyry1)benzene (Bis-4MSB). The present study focusses on the effect of substituents and solvent on the emission properties of these dyes. Specifically, we have reinvestigated the effect of solvent on fluorescent quantum yields of these dyes. In contrast to earlier studies on DSB,14 we find very little solvent dependence of the fluorescent quantum yield for any of these molecules. The steric effect of ortho substitution of the terminal phenyls on the spectral properties of the ~
~~
~~
~
~~
~
'General Dynamics, Pomona, CA 91766. 0022-3654181 12085-0144$01.OOlO
(3) H. Furumato and H. Ceccon, J.Appl. Phys., 40,4204 (1969). (4) J. T. Warden and L. Gough, Appl. Phys. Lett., 19, 345 (1971). (5) H. Telle, U. Brickman, and R. h u e , Opt. Commun., 24,248 (1978). ( 6 ) J. Kuhl, H. Telle, R. Schieder, and U. Brinkman, Opt. Commun., 24, 251 (1978). (7) G. W. Scott, L. D. Talley, and A. J. Cox, Springer Ser. Chem. Phys., 3, 187 (1978). (8) D. E. Damschen, J. R. Richards, G. W. Scott, L. D. Talley, and A. J. Cox, Springer Ser. Chem. Phys., 4, 59 (1978). (9) A. Heller, J. Chem. Phys., 40, 2839 (1964). (10) I. B. Berlman, "Handbook of Fluorescence Spectra of Aromatic Molecules", 2nd ed, Academic Press, New York, 1971, p 327. (11) E. A. Andreeshchev, V. S. Viktorova, S. F. Kilin, Yu. P. Kwhakevich, and I. M. Rozman, Opt. Spectrosc., 24, 387 (1968). (12) S. Misumi and M. Kuwana, Bull. Chem. SOC.Jpn., 33,711 (1960). (13) S. Misumi, M. Kuwana, and M. Nakagawa, Bull. Chem. SOC.Jpn., 36, 143 (1962). (14),A. Nikitina, G. M. Fedyunina, L. A. Yanovskaya, V. A. Dombrovski, and V. F. Kucherov, Opt. Spectrosc., 30, 343 (1971).
0 1981 American Chemical Society
The Journal of Physical Chemistty, Vol. 85, No. 2, 1981 145
Fluorescence of Distyrylbenzenes
TABLE I1 : Stokes Shifts in Dioxane Solution
Stokes shift, molecule DSB Bis-4MSB
cm" 3950 4010
molecule Bis-2MOSB Bis-2MSB
Stokes shift, cm-' 4120 4830
TABLE 111: Fluorescence Quantum Yields (%) molecule
DSB Bis-2MSB Bis-4MSB Bis-2MOSB
cyclohexane
102.6 * 98.0 * 104.0 t 94.0 *
6.0 6.0 6.0 2.5
solvent toluene
heptane
104.6 * 3.0 99.5 * 2.3
91.4 t 2.1 87.0 c 2.1
Experimental Section Materials. Bis-2MSB was obtained as a laser-grade dye from New England Nuclear. DSB, Bis-2MOSB, and Bis-4MSB were all synthesized according to the method of Campbell and McD0na1d.l~ The DSB, thus prepared, was refluxed and recrystallized from boiling benzene with a trace of iodine added. Solvents used for these dyes, without further purification, included ethanol (Pharmco, 200 proof), heptane (Mallinckrodt, SpectrAR),cyclohexane (Mallinckrodt, SpectrAR), toluene (MCB, spectroquality), and dioxane (Aldrich, gold label). Procedures. Corrected emission spectra were obtained with a Farrand spectrofluorometer with an autoprocessor which can be used to obtain corrected excitation and emission spectra. Stock solutions of the dyes were prepared which gave a measured absorbance at the exciting wavelength (A,, = 365.1 nm; bandpass = 2.5 nm) of =0.5 in 1 cm. Absorption spectra of these solutions were obtained on a Cary 17. These solutions were accurately diluted by a factor of (625)-' to yield optically dilute sample solutions of concentrations
