Single molecules of terrylene in di-substituted naphthalenes crystallizing in the herringbone pattern

Abstract

2,3-Dichloronaphthalene (2,3-DCN) and 2,3-dibromonaphthalene (2,3-DBN) were synthesized, purified and used to grow single crystals in the form of thin plates. X-ray crystallographic studies, performed for the first time, showed that molecules in both isostructural crystals are arranged in the herringbone pattern. These crystals, lightly doped with terrylene (Tr), appeared to be very good systems for optical single-molecule studies. Fluorescence excitation spectra of single Tr molecules at 5 K in excess of the dominating purely electronic (0, 0) and intense vibronic line of ∼250 cm⁻¹ frequency had a new, “184 cm⁻¹” line, absent in the spectrum of isolated (D_2h) Tr. Quantum-chemistry calculations indicated that this new line was the fingerprint of the deformation of the Tr molecule in the crystal structure, which lowered its symmetry to C_2h.