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We report a zero-field optically detected magnetic resonance (ODMR) study under high pressure for triplet pyrimidine in benzene, pyrazine in benzene and in $p$-dichlorobenzene, and $s$-tetramethylpyrazine in durene. For azaromatics, the size of non-bonding orbital on the N atoms is smaller than that of an aromatic C-H fragment, therefore under moderate pressure, the interaction of a non-bonding electron with the neighboring atoms in a crystalline matrix is still attractive in nature. Thus pressure will stabilize the n-electron, resulting in an up-shift in energy of an $n\pi \ast$ state. This leads to a decrease in the spin-orbit coupling contribution to D in n$\pi \ast$ triplets of pyrimidine and pyrazine. Other contrasting behaviors are explained by the difference in crystalline packing. There is a large change in D and a multiplet splitting under high pressure for tetramethylpyrazine. These are ascribed to the presence of a pseudo Jahn-Teller interaction in this molecule.