Table 1. Classification of substituent effects on.

Substituent	Character relative to H	Orbital interaction	Narrowing effect of energy gap
‒COOH	Electron withdrawing	LUMO	Weak
	Electron withdrawing	LUMO	Weak
‒OH	Electron donating	HOMO	Weak
	Electron donating	HOMO	Moderate
‒NH2	Electron donating	HOMO	Moderate
‒N(CH3)2	Electron donating	HOMO	Moderate
	Electron donating	LUMO	Moderate
	Electron donating	LUMO	Moderate
	Electron donating	LUMO	Strong
	Electron donating	LUMO	Strong