Photophysics of 4a,5,10,15-tetra-azabenzo[a]naphth[1,2,3-de]anthracene (NTCQ, the ring-nitrogen isostere of tricycloquinazoline)

Abstract

The absorption spectra and the fluorescence and phosphorescence spectra, polarization, quantum yields and lifetimes of the ring-nitrogen isostere of tricycloquinazoline (NTCQ) have been investigated over a range of solvents and temperatures. The properties of the lower energy excited states and of the ground state of NTCQ are discussed in terms of the above data. S₁ is n, π* and transforms with A″, whereas S₂ is π, π* and transforms with A′. Vibronic coupling occurs through a″ perturbing vibrations. With increasing polarity, dielectric constant and viscosity of the solvent the S₁ state undergoes an increasing blue-shift and becomes quasi-degenerate with S₂, presumably on account of a pseudo-Jahn–Teller coupling.