about the brightness at the ends - I'm pretty sure that is due to the fact that this is a pi-conjugated system; that is, the pi-bonded electrons can jump around

about the brightness at the ends - I'm pretty sure that is due to the fact that this is a pi-conjugated system; that is, the pi-bonded electrons can jump around the whole molecule. This, together with the fact that the molecule is finite in size, means that the pi electrons are confined to a rectangle of lower potential energy, and when you solve the quantum mechanics (similarly to the quantum harmonic oscillator) you'll find higher electron density at the edges of the confining potential.