Dear Kai Lin Woon,

there is no general answer to this question. What molecules do you use for your emission measurements?

Regards

Max

complex organic molecule containing amine created from hydrothermal process.... the above question is not carbonyl group but amine...

@ mr Woon

the carbonyl group itself absorbs and emits radiation: formaldehyde in the gas-phase is THE example

Absorption to a n-pi* state is weak. This means that the rate of fluorescence is small. Or in other words that the lifetime is long

The molecule can also lose its energy via 2 other processes:

-internal conversion: a transition to the ground state

-intersystem crossing: transition to a triplet state

Such processes can have a much higher rate and therefore the fluorescence is too weak to observe

Further reading: Jablonski scheme

The simplest I found but still complex:

http://web.mit.edu/solab/Documents/Assets/So-Fluorescence%20spectrophotometry.pdf

Is there any reason why n–π* fluorophores transition tends to undergo inter-system crossing?