PHOTOPHYSICS OF A STERICALLY CROWDED TERTIARY-SATURATED AMINE - TRIISOPROPYLAMINE

The spectroscopic and photophysical properties of triisopropylamine (TIPA), a sterically overcrowded amine, are reported in the vapor phase and in n-hexane and tetrahydrofuran solution. On the basis of available experimental data and several semiempirical and ab initio quantum mechanical calculations, it is concluded that TIPA is planar or nearly planar in the ground state. Inversion barriers of NH3, trimethylamine, and TIPA are examined with the aid of computational methods. In the vapor phase, E00 and E(vert) are 36 550 and 38 000 cm-1, respectively, for the S0 --> S1 transition. The zero-pressure-extrapolated fluorescence lifetime and quantum efficiency are 57.8 ns and 0.79, respectively. Its properties are compared with other tri-C3-substituted amines, such as tri-n-propylamine (TNPA) and the cage amine, I-azabicyclo[3.3.3]undecane (ABCU). As compared with TNPA, the S0 --> S1 absorption of TIPA is red shifted and its Stokes shift is smaller. The cap structure of ABCU results in the S0 <-- --> S1 transitions being very vertical. Multielectron configuration interaction calculations using MNDO are used to determine the E00 and E(vert) values of the amines; the results are compared with experiment.