Triplet States and Triplet Excitons in Chemically Mixed Crystals of Acridine with Anthracene

Abstract

Spectral and temporal characteristics and their temperature dependence for the long-lived (phosphorescence and delayed fluorescence) emissioii of chemically mixed crystals of acridine II (host) with anthracene (guest) were studied under conditions of various spectral resolutions and different modes of excitation. The energy of 0-0 transitions of exciton band and of trap states have been determined and the nature and energy scheme of the triplet states of crystals have been established. The ckplex arrangement of host molecules into two different pairs in the crystal structure of acridine II is revealed in the energetic "doublet" structure of the trap states for both, . the shallow and the deep traps (of acridine and of anthracene origin, 'respectively). Migration of triplet excitatioii energy in these chemically mixed crystals is controlled predominantly by the triplet-triplet annihilation of excitons (either heterogeneous or hkogeneous) almost in the whole temperature range. The formation of triplet excimers of acridine was definitely ruled out.

Emission of Acridine and its Aggregates Isolated in the Neon Matrix

“…Since the observed bandwidths in the fluorescence excitation spectra are much wider than the spectral instrumental resolution (which is of 0.2 cm-1 ), these bands are inhomogeneously broadened and a part of such broadening may probably be due to the coupling with lattice phonons characteristic for a given site in the matrix. However, under conditions of our experiments we should take into account also a possibility of the formation of different complexes or aggregates of ACD, e.g., the formation of sandwich-like excimers as those confirmed for neat and mixed ACD crystals [11,13,21,22], and the resonance aggregates such as those found in the crystalline host matrix of anthracene [24,25]. The formation of such aggregations would result in additional broad bands or continuous background in the fluorescence and fluorescence excitation spectra.…”

“…3a). The 0-0 band of the phosphorescence is positioned at 16016 cm-1 and thus it has a higher energy than the 0-0 band of phosphorescence of ACD in chemically mixed crystal of ACD (host) with anthracene -15691 cm -1 [25] and in crystalline host matrices of fluorene -15749 cm -1 [23] and of dimethylnaphthalene -15813 cm -1 [17] or in PMMA matrix (at 77 K) -15800-15900 cm -1 [5]. The observed phosphorescence spectrum contains such vibrational frequencies as 246, 401, 622, 1170 and 1271 cm -1 , all of them have been previously observed in the phosphorescence spectrum of ACD in the -fluorene crystalline host matrix at 2.2 K [23], and also frequencies of 790, 876 and 1410 cm -1 known from either IR or Raman spectra of ACD [26].…”

“…So far, earlier reports on the formation of ACD complexes in rigid media [3,11,13,[21][22][23] have been confirmed independently [24,25] only for the case of singlet excimers of ACD in crystalline phase (in crystalline modification II). A possibility of the formation of ACD excimers is inherently connected with the crystal structure and packing conditions which provide and assure a preferable and necessary pre-orientation of interacting ACD molecules.…”

“…Their sensitivity to the solvent and to the phase conditions seems to be exceptional even when compared with other molecules *The results of this paper were initially presented at The Jabłοński Centennial Conference on Luminescence and Photοphysics, Juły [23][24][25][26][27]1998, Toruń, Połand.…”

Spectroscopy and Photophysics of Monoazaphenanthrenes III. Luminescence of Phenanthridine and 7,8-benzoquinoline in Crystalline State

“…Exactly the same kind of fluorescence and phosphorescence spectra were observed in the case of acridine II crystal -a broad and structureless fluorescence spectrum, and a very rich and sharp structure of phosphorescence spectrum. Investigations of phosphorescence and its structure, at deep temperatures (1.7 K) and under high resolution conditions, have definitely ruled out triplet excimers as a way for dissipation of singlet excitons [31].…”