In the 3 examples, "interested", "frightening", and "excited" are not participles; they are adjectives that look like participles.
See a list in
http://www.langust.ru/unit_co/unit023c.shtmly
Present participles are placed after auxiliary verb-to-be's (is, am, are, was, were, be) to be the verb for the "continuous tense", e.g.: The lumberjacks are cutting a tree.
When a present participle does not follow a verb-to-be, it is not functioning as a verb, but a verbal, for example: Cutting a tree, the lumberjacks ignored the heavy rain.
Many verb + ing are not used as participles, but gerunds, which is another form of verbal, functioning as a noun or noun phrase, e.g.The lumberjacks are tired after cutting a tree.
Past participles are placed after auxiliary verb-to-be's to become the "passive voice", for example: He was fired by his boss.
Past participles are also placed after auxiliary verb-to-haves's (have, has, had) to become the "perfect tense", e.g. The boss had fired him.
When a past participle does not follow a verb-to-be or verb-to-have, it is not functioning as a verb, but a verbal (functioning as adjective), e.g. Fired from the job, he is worried.
Present perfect tense describes an action which has been completed between a time in the past and now. e.g. He has tried to stop gambling.
Present perfect continous tense describes an action which has been continuing from a time in the past, to now, and is still happening, e.g. He has been trying to stop gambling.
Past perfect tense describes an action which occued between a time in the past to another time in the past, e.g. He had tried to stop gambling for several months last year.
Finally, "to be" is the infinitive of the auxiliary verb-to-be. Infinitive = to + verb, e.g. He is likely to arrive late. When the auxiliary verb is used as the verb in an infinitive, it becomes "to be", e.g. He is likely to be late.
