Supporting Information

Transcription

1 Supporting Information Photophysical Properties of the Series fac- and mer-(-phenylisoquinolinato-n^c ) x (- phenylpyridinato-n^c ) 3-x Iridium(III) (x = to 3) Joseph C. Deaton *,, Ralph H. Young, Jerome R. Lenhard, Manju Rajeswaran, and Shouquan Huo *, Eastman Kodak Company, Rochester, NY, 4650; Department of Chemistry, East Carolina University, Greeneville, NC 7858 Work carried out at Eastman Kodak Company, Rochester, New York 4650, was done prior to December, 009 * To whom correspondence should be addressed. jdeaton@rochester.rr.com (J.C.D); huos@ecu.edu (S. H.).

2 Synthesis Additional procedures for thermal isomerization of mer-ir(-piq) (ppy) in solid state. Method C: A sample of mer-ir(-piq) (ppy) (0 mg, mer/fac ratio >99:) was placed in a small ampoule. The ampoule was sealed under high vacuum and placed in an oven. The temperature of the oven was set to 300 C. After 3 h, the ampoule was taken out and cooled to room temperature, the mer/fac ratio of the sample was determined by HPLC to be 4:96 (area). Method D: A sample of mer-ir(-piq) (ppy) (50 mg, mer/fac ratio >99:, HPLC area) was placed in a opened small vial. The vial was placed into a heating apparatus with an inlet connected with a dry argon line and with an outlet connected to a bubbler. The heating apparatus was purged for 30 min before heating then maintained with a slow argon flow during heating. The material was heated at 90 C for 48 h. After cooling to room temperature, the vial was taken out and the mer/fac ratio of the sample was determined by HPLC to be 7:93 (HPLC area). Sublimation. The vapor pressures of fac-(piq) 3 and fac-ir(piq) (ppy) at various temperatures were measured by the Knudsen effusion technique (Knudsen, M. Ann. Phys. 909, 8, ) and are shown in Figure S. The enthalpy and entropy of sublimation for the median temperature of measurement, T m, were calculated from a linear fit to the experimental data using the integrated form of the Clausius-Clayperon equation, eq SI- (P 0 = atm, R = gas constant). The values are listed in Table S, along with those of fac-ir(ppy) 3 for reference.

3 3 ln( P / P0 ) = S / R H RT (SI-) sub m sub m / Table SI-. Enthalpy and Entropy of Sublimation for fac-ir(ppy) 3, fac-ir(piq) 3 and fac- Ir(piq) ( ppy) at median temperatures of measurement. Compound sub H m (kj mol ) sub S m (J K mol ) T m (K) fac-ir(ppy) ±.8 9. ± fac-ir(piq) ± ±. 568 fac-ir(piq) (ppy) 0.4 ± ± Interestingly, the data in Figure SI- and Table SI- reveal that the greater volatility of fac- Ir(piq) (ppy) relative to that of fac-ir(piq) 3 arises from an increased entropy of sublimation, not from any significant difference in enthalpy of sublimation. The vapor pressure of fac- Ir(piq)(ppy) was not measured, but it was found in vapor deposition of OLEDs (vide infra) that the temperature required for deposition at the same rate followed in the order fac-(piq) 3 > fac-ir(piq) (ppy) > fac-ir(piq)(ppy). Figure SI-. Vapor pressures determined by Knudsen effusion technique for fac-ir(piq) 3 and fac-ir(piq) (ppy).

4 4 Photophysical Properties Figure SI-. Absorption spectra of the series fac-ir(piq) x (ppy) 3-x (x = to 3) in -MeTHF at 95 K. Figure SI-3. Phosphorescent decays of fac-ir(piq)(ppy) in PMMA (0.05 wt %) at selected temperatures. Emission detected at 60 nm after pulsed excitation at 485 nm.

5 5 Fig SI-4. Absorption of the series mer-ir(piq) x (ppy) 3-x in -MeTHF at 95 K. Fig SI-5. Absorption comparison on an expanded scale of mer- and fac-ir(piq)(ppy) in - MeTHF at 95 K.

6 6 Figure SI-6. Phosphorescent decays of mer-ir(piq)(ppy) in PMMA ( wt %) at selected temperatures. Emission detected at 580 nm after pulsed excitation at 485 nm. Correction of the spectra and quantum yields for fac-ir(piq)(ppy). The spectra and quantum yields reported in the text for fac-ir(piq)(ppy) represent a sample containing a 5% impurity of fac-ir(piq) (ppy). As shown below, the effects of the impurity are quite small. Quantities relating to the pure compounds, fac-ir(piq)(ppy) and fac-ir(piq) (ppy) are indicated by a subscript or ; quantities relating to the impure fac-ir(piq)(ppy) are indicated by a subscript i. The concentrations were in the ratio c /c = 5/95. A straightforward calculation leads to eq SI-. Thus, the correction to the absorption spectrum of fac-ir(piq)(ppy)

7 7 ε ε 055 ( ε ) i + 0. i ε (SI-) amounts to 5.5% of the difference between the spectra of the impure fac-ir(piq)(ppy) and the pure fac-ir(piq) (ppy). At room temperature and λ ex = 355 nm, the extinction coefficient of fac-ir(piq) (ppy) is almost equal to that of fac-ir(piq)(ppy) (Figures and SI-). A straightforward calculation starting from the quantum yields in Table 4 shows that the correction to the quantum yield of fac-ir(piq) (ppy) is less than 0.00 in -MeTHF. Since the quantum yields of Ir(piq) (ppy) and the impure fac-ir(piq)(ppy) are equal in PMMA (Table 5), the quantum yield of pure Ir(piq) (ppy) is the same. The emission spectra of fac-ir(piq)(ppy) and fac-ir(piq) (ppy) shown in Fig 3 are quantitatively so similar that an appropriately weighted subtraction of one from the other cannot have an appreciable effect. The emission spectra at low temperature, Figs. 4 and 5, are more different, especially in the blue edges, so it is perhaps worthwhile to consider the correction for the impurity. Let s (λ), s (λ), and s i (λ) be the emission spectra as functions of wavelength, normalized to as in Figs 4 and 5. The spectrum of pure fac-ir(piq)(ppy) can be evaluated using eq SI-3a, where the coefficient X is given by eq SI-3b. s ( s ) = s + X (SI-3a) i i s X c = c ε ε Φ Φ A A (SI-3b) The quantities A and A are the areas under the curves in the normalized spectra of Fig. 5. Their ratio is approximately at each temperature. The ratio of quantum yields is also

8 8 approximately at each temperature. The ratio of extinction coefficients pertains to the wavelength of excitation, 458 nm, where ε /ε =.3. The concentration ratio is 5/95. Therefore, X 0.07, and the normalized emission spectrum of pure fac-ir(piq)(ppy) is given by eq SI-3c. ( s ) s si i s (SI-3c) The correction amounts to about 7% of the difference between the spectra of the impure fac- Ir(piq)(ppy) and the pure fac-ir(piq) (ppy). The main effect is to increase the intensity of the blue edge by several percent. Correction of the zero-field parameters for fac-ir(piq)(ppy). The zero-field parameters reported for fac-ir(piq)(ppy) in Table 6 were evaluated without taking the 5% fac- Ir(piq) (ppy) impurity into account. The decay constants k obs were evaluated from the initial slopes of the photoluminescence decay curves on semilogarithmic plots. The corrected values cited in the text were obtained by fitting the data to a formula for k obs that includes the contributions of the impurity to the observed decays. The derivation of this formula is given in the following. For the Ir(piq)(ppy) and Ir(piq) (ppy) components of the impure sample, let k and k be the respective decay constants, c and c be the molar concentrations, ε and ε be the extinction coefficients, Φ and Φ be the quantum yields, and f and f be the fractions of emitted photons that are counted by the detector. The initial concentrations of excited states for the two components of the impure sample are Aε c and Aε c, respectively, where A is a proportionality constant. The subsequent concentrations are represented by decaying

9 9 exponentials, Aε c exp(-k t) and Aε c exp(-k t). The radiative rate constants are k Φ and k Φ, and the numbers of photons emitted per second are k Φ Aε c exp(-k t) and k Φ Aε c exp(-k t). The numbers of photons detected per second are f k Φ Aε c exp(-k t) and f k Φ Aε c exp(-k t). The total counting rate, I(t), is the sum of the two individual rates, eq SI-4. ( t) = A[ f k Φ c exp( k t) + f k Φ ε c ( k t) ] I exp ε (SI-4) Evaluating d ln I( t) dt at t = 0 gives an expression for the observed decay rate of the impure mixture as an initial slope, eq SI-5a. The temperature-dependent values of k, the decay constant for the impurity, are known from experiment. The coefficient B is given in terms of other experimental quantities by eq SI-5b. k + B k k obs = k (SI-5a) k + B k c B= c ε ε f f Φ Φ (SI-5b) A Boltzmann formula, eq SI-5c, expresses k in terms of the temperature and the zero-field splittings and decay rates of the triplet sublevels for pure fac-ir(piq)(ppy). k I + k II exp( EII / kt ) + k III exp( EIII / kt ) k = (SI-5c) + exp( E / kt ) + exp( E / kt ) II III

10 0 Combining eqs SI-5a to SI-5c provides a theoretical formula for the initial slope of the photoluminescence decay of the impure sample of fac-ir(piq)(ppy). The ratio c /c was 5/95 from the HPLC analysis. At 485 nm and room temperature, the ratio ε /ε is.40 (see Figs. and SI-). Because the absorption spectra are not highly structured, the ratio ε /ε was assumed to be independent of temperature. Because the emission spectra are similar, the ratio f /f is approximately at each temperature (see text and Figs. 3 and 5). At room temperature, the pure fac-ir(piq) (ppy) and the impure fac- Ir(piq)(ppy) have equal quantum yields in PMMA, so the pure fac-ir(piq)(ppy) must have the same value, and Φ /Φ =. The temperature dependence of B is determined by the temperature dependence of Φ /Φ. Individually, Φ and Φ are proportional to the integrated intensities of the spectra, and the temperature dependences of the observed intensities were used to determine the ratio Φ /Φ as a function of temperature. The zero-field splittings and decay rates of the triplet sublevels for pure fac- Ir(piq)(ppy) were evaluated from the experimental data by fitting the theoretical expression for the initial slopes, eq SI-5a to SI-5c, to the observed values for the sample of fac- Ir(piq)(ppy) containing 5% of fac-ir(piq) (ppy). A least-squares procedure was used, assuming equal relative uncertainties for the data points. The best-fit curve was similar to that shown in Fig. 6, with a slightly better fit (smaller r.m.s. deviation from the data). Although eq SI-4 is formally biexponential, the decays I(t) evaluated with the corrected parameters appeared approximately single-exponential because the second term in eq SI-4 is relatively small. The corrected parameters for pure fac-ir(piq)(ppy) are shown in

11 comparison to the uncorrected values in Table SI- below, and are also reported in the text. The corrections are not significantly larger than the standard deviations of the parameters. Table SI-. Zero-field splittings and decay rate constants for triplet sublevels of fac- Ir(piq)(ppy) without and with correction for the effect of the 5% fac-ir(piq) (ppy) impurity. E II (σ) E III (σ) k I (σ) k II (σ) k III (σ) (cm ) (cm ) (0 4 s ) (0 5 s ) (0 6 s ) uncorrected 4.5(.9) 00.6(5.9).58(0.08).4(0.6).6(0.7) corrected 5.6(3.) 06.6(7.4).56(0.07) 0.95(0.).78(0.0)

12 Figure SI-7 H NMR spectrum of fac-ir(piq) 3 (in CH Cl ).

13 Figure SI-8 H NMR spectrum of fac-ir(piq) (ppy) (in CH Cl ). 3

14 Figure SI-9. H NMR spectrum of fac-ir(piq)(ppy) (in CH Cl ). 4