Absorption and fluorescence spectra of C60 fullerene concentrated solutions in hexane and polystyrene at 77–300 K

Abstract

The locations of the 0 0 0 -bands for S 1 ← S 0 and S 1 → S 0 transitions have been found for C 60 solutions in hexane. It is shown that the profile of the S 1 ← S 0 band is mainly shaped by h u (4), t 1u (4)-and h g (1), a g (2)-modes that are active in absorption. Bands involving the h u (4)-and t 1u (4)-modes in the emission process have also been identified in the fluorescence spectrum. The appearance of the 0 0 0 -band in the forbidden 1 1 T 1g ← 1 1 A g transition is explained by symmetry reduction in the C 60 +environment system due to the interaction of electrons with local phonons. The temperature coefficients of the red shift for the 256.3-and 328.3-nm bands of allowed 1 T 1u ← 1 1 A g transitions for C 60 in hexane are equal to -1.45 and -0.46 cm -1 ⋅K -1 , respectively. The peak and half-width values of the 337.2-nm band for C 60 in polystyrene remain unchanged on cooling to 77 K. Absorption in the 700-800-nm region for concentrated hexane solutions of fullerene at 292 K results from the production of (C 60 ) n -clusters.Keywords: vibronic spectra, broadening, temperature effect, dispersion interactions, 0-0 band, solvatochromic shift, (C60)n-clusters.Introduction. The spectral properties of fullerene C 60 are interesting because of the broad application of materials based on carbon nanoparticles in science, industry, and medicine [1][2][3][4][5][6][7]. The solution of several astrophysical problems was also directly related to the study of the spectral properties of fullerenes [8,9]. Polymers that can be used as a basis for creating optical emission limiters, photo-conducting materials, and materials suitable for transforming solar energy into electrical are being sought [3, 10-12]. For example, the ability of C 60 bound covalently to phthalocyanine to transform long-lived (0.2 ms) photoinduced states with charge separation [11] was used to fabricate a solar cell in which the polymer matrix acted as an external light-collecting antenna and effected charge transfer into the reaction center, the phthalocyanine-fullerene dyad [12].Fullerene C 60 is a spherical molecule with point-group symmetry I h . The unique structure is responsible for its unusual photophysical properties that differ substantially from those of heterocyclic compounds. The vibronic spectra of C 60 exhibit both allowed and symmetry-forbidden transitions. Extensive theoretical and experimental investigations enabled bands and lines in spectra of fullerene C 60 to be identified [9,[13][14][15][16][17][18][19][20][21][22][23][24][25][26] and general trends of the shift upon changing the nature of the medium to be explained [13,14]. As a rule, n-alkanes were used as the solvents [13,14]. The bands and symmetry assignment of transitions for C 60 have been described in detail [16]. Measurements at low temperatures were made in glassy solvents such as toluene [15], 3-methylpentane, and hexane [16,17] at 77 K, in inert-gas matrices at 4.2 K and lower [9,18,19,26], and in the gas phase (in molecular beams cooled by expansion) [21][22][23][24]....

Influence of the aggregate state on band structure and optical properties of C60 computed with different methods

“…59 This is because this formalism, 46 although it does depend on integrals over occupied and unoccupied Kohn-Sham orbitals of the sort ⟨ | ⟩, ⟨ | ⟩, 46 does not depend on them in the same extremely sensitive way as TD-DFT or the dipole approximation in which the dependence (and therefore any errors) is amplified due to the kernel in the overlap integral. The spectrum computed with B3LYP is comparable with that computed with TD-DFT, which appears to be quantitatively accurate 17,23 for both the onset of absorption (from about 3 eV) and magnitude of the extinction coefficient of the first peak around 4 eV (on the order of 20,000 L mol -1 cm -1 ).…”

“…1 of Ref. 23 The aggregation effect on the spectrum computed with B3LYP, where the spectrum of a single molecule is in semi-quantitative agreement with the experiment, 23 is relatively reasonable but appears exaggerated vs experiment, while that computed with PBE is unreasonable. 56 This is likely a method failure.…”

“…Specifically, by comparing the experimental spectrum of C60 in Ref. 23 measured in a non-polar solvent, which can serve as an estimate of single-molecule absorption, to that of Ref. 56 , which was measured in thin film, one observes that aggregation is expected to cause a mild redshift and an appearance of a shoulder (compare FIG.…”

Direct observation of photocarrier electron dynamics in C60 films on graphite by time-resolved two-photon photoemission

“…Formation of the lowest-lying excitons such as S 1 and T 1 would be another pathway of hot electron relaxation that may induce the photoemission by process 2a described above. The central energy of S 1 (0-0 transition) is known to be 2.0 eV, whereas the absorption band of S 1 distributes from 430 to 670 nm in wavelength 58 . Taking into account the energy of the HOMO ( E F −2.2 eV), the higher energy component of S 1 is expected to appear around the low energy cut-off ( E F + 0−0.7 eV in the intermediate energy ( E final − hν )) and also to exhibit relaxation dynamics on the ps-ns time scale.…”

Absorption spectra of alkali-C60nanoclusters

“…Comparison of the present calculated spectrum on isolated C60 with experimental data is difficult since the experimental measurements have been performed either in hot gas phase [53] or embedded in a condensed medium [52,[53][54][55][56] [56]. A good discussion about the comparison experiment-theory can be found in Ref [52].…”