taking sunrise need to wake up very early, you need to be at the site around 6.30am, taking public transport is not always possible. and you need to have some experience to know where is the best exact spot to have sunrise.
try Sunset first, which is more easy, if you miss it, you still can take dusk light.
It'll be great to just have a clear horizon for sunset without the city buildings but that's not possible in S'pore. For that, you'll need to travel to West Malaysia. Can also consider the coastal areas around Tanah Merah ferry terminals.
Just saw a thread in the 'gatherings and outings'. Robin is organising a sunset shoot this Sat (9 Jun) at Labrador Park... can consider it too...